Alkaloid Synthesis: (+)-Deoxoprosopinine (Krishna), Alkaloid (–)-205B (Micalizio), FR901483 (Huang), (+)-Ibophyllidine (Kwon), (–)-Lycoposerramine-S (Fukuyama), (±)-Crinine (Lautens)

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Aldol Condensation ◽  
Indian Institute ◽  
Chiral Auxiliary ◽  
Full Account ◽  
Ene Reaction ◽  
Alkaloid Synthesis ◽  
Stereogenic Centers ◽  
Sequential Addition ◽  
Vinyl Group ◽  
The University

Palakodety Radha Krishna of the Indian Institute of Chemical Technology observed (Synlett 2012, 2814) high stereocontrol in the addition of allyltrimethylsilane to the cyclic imine derived from 1. The product piperidine 2 was carried onto (+)-deoxoprosopinine 3. Glenn C. Micalizio of Scripps Florida condensed (J. Am. Chem. Soc. 2012, 134, 15237) the amine 4 with 5. The ensuing intramolecular dipolar cycloaddition led to 6, which was carried onto the Dendrobates alkaloid (–)-205B 7. Pei-Qiang Huang of Xiamen University showed (Org. Lett. 2012, 14, 4834) that the quaternary center of 9 could be established with high diastereoselectivity by activation of the lactam 8, then sequential addition of two different Grignard reagents. Subsequent stereoselective intramolecular aldol condensation led to FR901843 10. More recently, Professor Huang, with Hong-Kui Zhang, also of Xiamen University, published (J. Org. Chem. 2013, 78, 455) a full account of this work. In an elegant application of the power of phosphine-catalyzed intermolecular allene cycloaddition, Ohyun Kwon of UCLA added (Chem. Sci. 2012, 3, 2510) 12 to the imine 11 to give 13. The cyclization elegantly set two of the four stereogenic centers of (+)-ibophyllidine 14. Tohru Fukuyama of the University of Tokyo initiated (Angew. Chem. Int. Ed. 2012, 51, 11824) a cascade cyclization between the enone 15 and the chiral auxiliary 16. The product lactam 17 was carried onto (–)-lycoposerramine-S 18. Mark Lautens explored (J. Am. Chem. Soc. 2012, 134, 15572) the utility of the intramolecular aryne ene reaction, as illustrated by the cyclization of 19 to 20. Oxidation cleavage of the vinyl group of 20 followed by an intramolecular carbonyl ene reaction led to (±)-crinine 21.

C-O Ring Natural Products: (-)-Serotobenine (Fukuyama-Kan), (-)-Aureonitol (Cox), Salmochelin SX (Gagné), Botcinin F (Shiina), (-)-Saliniketal B (Paterson), Haterumalide NA (Borhan)

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Indole Alkaloid ◽  
Chiral Auxiliary ◽  
Michigan State University ◽  
State University ◽  
Ene Reaction ◽  
Enantiomerically Pure ◽  
Cambridge University ◽  
Stereogenic Centers ◽  
Ready Access ◽  
The University

Tohru Fukuyama of the University of Tokyo and Toshiyuki Kan of the University of Shizuoka devised ( J. Am. Chem. Soc. 2008, 130, 16854) the chiral auxiliary-directed Rh-mediated cyclization of 1, setting the two stereogenic centers of 2 with high stereocontrol. The ester 2 was carried on to the indole alkaloid (-)-Serotobenine 3. In the course of a synthesis of (-)-Aureonitol 6, Liam R. Cox of the University of Birmingham developed (J. Org. Chem. 2008, 73, 7616) the diastereoselective intramolecular addition of an allyl silane 4 to give the tetrahydrofuran 5. In analogy to what is known about the intramolecular ene reaction, the diastereocontrol observed for this cyclization may depend on the allyl silane being Z. Michel R. Gagné of the University of North Carolina found (J. Am. Chem. Soc. 2008, 130, 12177) that the Ni-catalyzed coupling of organozinc halides could be extended to glycosyl halides such as 7. This opened ready access to C -alkyl and C -aryl glycosides, including Salmochelin SX 10. Isamu Shiina of the Tokyo University of Science established (Organic Lett. 2008, 10, 3153) that the acid-mediated cyclization of the Sharpless-derived epoxide 10 proceeded with clean inversion, to give 11. The highly-substituted tetrahydropyran core 11 was then elaborated to the antifungal Botcinin F 12. Ian Paterson of Cambridge University optimized (Organic Lett. 2008, 10, 3295) the Pd-catalyzed spirocyclization of the ene diol 13, leading to 14, the enantiomerically-pure bicyclic core of (-)-Saliniketal B 15. Haterumalide NA 18 presented the particular challenge of assembling the geometrically-defined chloroalkene, in addition to closing the macrolide ring. Babak Borhan of Michigan State University addressed (J. Am. Chem. Soc. 2008, 130, 12228) both of these challenges together, electing to employ a chlorovinylidene chromium carbenoid, as developed by Falck and Mioskowski, to effect the macrocyclization of 16 to 17.

Alkaloid Synthesis: Penaresidin A (Subba Reddy), Allokainic Acid (Saicic), Sedacryptine (Rutjes), Lepistine (Yokoshima/Fukuyama), Septicine (Hanessian), Lyconadin C (Dai)

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Marine Sponge ◽  
Indian Institute ◽  
Chemical Technology ◽  
Starting Material ◽  
Allylic Oxidation ◽  
Actomyosin Atpase ◽  
Alkaloid Synthesis ◽  
Purdue University ◽  
The University ◽  
Biogenetic Precursor

Penaresidin A 3, isolated from the Okinawan marine sponge Penares sp., is a potent activator of actomyosin ATPase. B. V. Subba Reddy of the Indian Institute of Chemical Technology prepared (Tetrahedron Lett. 2014, 55, 49) the azetidine ring of 3 by mesyl­ation of the hydroxy sulfonamide 2, derived from 1, followed by cyclization. Allokainic acid 6 has become a useful tool for neurological studies. Radomir N. Saicic of the University of Belgrade found (Org. Lett. 2014, 16, 34) that the Tsuji–Trost cyclization of 4 to 5 proceeded with high diastereoselectivity, presumably by way of the enamine of the aldehyde. Floris P. J. T. Rutjes of Radboud University Nijmegen prepared (Org. Lett. 2014, 16, 2038) the starting material 7 for (−)-sedacryptine 9 via an enantioselective Mannich addition. The reagent of choice for the Aza–Achmatowicz rearrangement of 7 to 8 proved to be mCPBA. The intriguing tricyclic alkaloid (−)-lepistine 12 was isolated from the mushroom Clitocybe fasciculate. En route to the first-ever synthesis of 12, Satoshi Yokoshima and Tohru Fukuyama of Nagoya University cyclized (Org. Lett. 2014, 16, 2862) the gly­cidol-derived sulfonamide 10 to the azacycle 11. (+)-Septicine 15 is the biogenetic precursor to the phenanthrene alkaloid (+)-tylophorine. Stephen Hanessian of the Université de Montréal prepared (Org. Lett. 2014, 16, 232) 15 by condensing the proline-derived ketone 13 with the aldehyde 14. Mingji Dai of Purdue University elaborated (Angew. Chem. Int. Ed. 2014, 53, 3922) the amine 16 to the enone 17 by intramolecular Mannich alkylation followed by methylenation and allylic oxidation. Condensation with the sulfoxide 18 then delivered lyconadin C 19.

Construction of Arrays of Stereogenic Centers: The Zhang Synthesis of (+)-Podophyllotoxin

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Chemistry ◽  
Conjugate Addition ◽  
Chiral Auxiliary ◽  
Stanford University ◽  
Enol Ethers ◽  
University Of Technology ◽  
Stereogenic Centers ◽  
Diastereoselective Addition ◽  
University Of Bristol ◽  
The University

Varinder K. Aggarwal of the University of Bristol showed (Angew. Chem. Int. Ed. 2009, 48, 1149) that condensation of a boronic ester 2 with a metalated aziridine 1 led, after oxidation, to the defined amino alcohol 3. Hisashi Yamamoto of the University of Chicago developed (Angew. Chem. Int. Ed. 2009, 48, 3333) conditions for the diastereoselective addition of an organometallic to an α-nitrosylated aldehyde, to give, after reduction, the diol 6. Xiaoyu Wu of Shanghai University and Gang Zhao of the Shanghai Institute of Organic Chemistry designed (Adv. Synth. Cat. 2009, 351, 158) an organocatalyst that mediated the enantioselective addition of hydroxyacetone 7 to a range of aldehydes. Andrew G. Myers of Harvard University found (J. Am. Chem. Soc. 2009, 131, 5763) that trialkylaluminum reagents opened epoxides of enol ethers at the more substituted position, delivering protected diols such as 10. Keiji Maruoka of Kyoto University created (Angew. Chem. Int. Ed. 2009, 48, 1838) an organocatalyst for the addition of an aldehyde 11 to an imine 12, to give 13. Markus Kalesse of Leibnitz Universität Hannover showed (Tetrahedron Lett. 2009, 50, 3485) that an organocatalyst could mediate the selective γ-reactivity of 15, leading to 16. Barry M. Trost of Stanford University found (J. Am. Chem. Soc. 2009, 131, 1674) that an organocatalyst directed the addition of diazoacetate 18 to an aldehyde, to give, after further reaction with a trialkylborane, the syn aldol product 19. Professor Trost also demonstrated (J. Am. Chem. Soc. 2009, 131, 4572) that a related complex mediated the conjugate addition of 22 to 21. Enantioselective construction of arrays of alkylated stereogenic centers is a particular challenge. Ji Zhang, then at Pfizer, found (Tetrahedron Lett. 2009, 50, 1167) that the chiral auxiliary of 24 directed both the conjugate addition and the subsequent protonation, and also allowed the product 25 to be brought to > 98% purity by crystallization. Tönis Kanger of Tallinn University of Technology developed (J. Org. Chem. 2009, 74, 3772) an organocatalyst for the conjugate addition of aldehydes to nitrostyrenes such as 26 to give 27.

Enantioselective Synthesis of Lactones and Cyclic Ethers

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Hydroxy Acid ◽  
Addition Product ◽  
Single Step ◽  
Indian Institute ◽  
Cyclic Ethers ◽  
University Of Texas ◽  
Complementary Approach ◽  
Stereogenic Centers ◽  
The University ◽  
Work Up

Developments in organocatalysis have turned toward the enantioselective construction of lactones. Shi-Wei Luo and Liu-Zhu Gong of the University of Science and Technology of China have found (J. Org. Chem. 2007, 71, 9905) that catalyzed addition of acetone to an α-hydroxy acid 1 proceeded with high ee. Esterification of the addition product followed by reduction and acid work-up delivered the lactone 4 with high dr and ee. In a complementary approach, Jean-Marc Vincent and Yannick Landais of the University Bourdeaux-1 showed (Chem. Commun. 2007, 4782) that catalyzed condensation of an aldehyde with an α-hydroxy acid 5 delivered the tetronic acid 8 in high ee. It may be that 8 could also be reduced with useful selectivity. Cong-Gui Zhao of the University of Texas, San Antonio has devised conditions (Organic Lett. 2007, 9, 2745) for the condensation of the keto phosphonates such as 10 with aldehydes to give, after oxidation, the δ-lactone 12. Carbohydrates such as glucose 13 are inexpensive, molecularly-complex starting materials. Subhash Chandra Taneja of the Indian Institute of Integrative Medicine, Jammu Tawi, has found conditions (J. Org. Chem. 2007, 72, 8965) for the single-step I2 -catalyzed transformation of 13 to 14, in which each of the alcohols have been differentiated. In a complementary approach described (Tetrahedron Lett. 2007, 48, 6389) by Tushar Kanti Chakraborty of the Indian Institute of Chemical Technology, Hyderabad, Ti-mediated reduction of 15 was shown to be highly diastereoselective, setting the two new stereogenic centers (marked by*) in 16. Building on work by Mead, Daniel Romo of Texas A&M has shown (J. Org. Chem. 2007, 72, 9053) that reductive cyclization of 18 also proceeded with high diastereocontrol, to give 19. As illustrated by the conversion of 20 to 21 reported (Tetrahedron Lett. 2007, 48, 7351) by Zsuzsa Juhász and László Somsák of the University of Debrecen, six-membered ring cyclic ethers can also be formed from carbohydrate precursors. Richard E. Taylor of the University of Notre Dame has taken advantage (Angew. Chem. Int. Ed. 2007, 46, 6874) of the “chemical chameleon” nature of a sulfone, using it both the stablilize the anion for intramolecular alkylation, to form 23, and as a leaving group, leading to 24.

C–N Ring Construction: The Hoye Synthesis of (±)-Leuconolactam

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
British Columbia ◽  
Indian Institute ◽  
South Florida ◽  
Chiral Auxiliary ◽  
Dipolar Cycloaddition ◽  
University Of Oxford ◽  
University Of British Columbia ◽  
Memory Of Chirality ◽  
Institute Of Technology ◽  
The University

Manas K. Ghorai of the Indian Institute of Technology, Kanpur depended (J. Org. Chem. 2013, 78, 2311) on memory of chirality during deprotonation to convert 1 to the aziridine 3. X. Peter Zhang of the University of South Florida demonstrated (Angew. Chem. Int. Ed. 2013, 52, 5309) that Co-catalyzed enantioselective aziridination is compatible with fluoro-aromatics such as 5. David M. Hodgson of the University of Oxford prepared (J. Org. Chem. 2013, 78, 1098) the azetidine 8 by double deprotonation of 7 followed by acylation. Laurel L. Schafer of the University of British Columbia assembled (Org. Lett. 2013, 15, 2182) 11 by Ta-catalyzed aminoalkylation of 10 with 9, followed by cyclization. Nicholas A. Magnus of Eli Lilly reduced (J. Org. Chem. 2013, 78, 5768) the ketone 12 to the alcohol 13 with high de and ee. Pei-Qiang Huang of Xiamen University effected (J. Org. Chem. 2013, 78, 1790) the reductive addition of 14 to 15 to give 16. The titanocene protocol reported (Angew. Chem. Int. Ed. 2013, 52, 3494) by Xiao Zheng, also of Xiamen University, effectively mediated similar transformations. En route to (–)-quinocarcin, Nobutaka Fujii and Hiroaki Ohno of Kyoto University cyclized (Chem. Eur. J. 2013, 19, 8875) 17 to 18 with high diastereoselectivity. Dipolar cycloaddition, long a workhorse of pyrrolidine synthesis, has been improved by enantioselective organocatalysis. For instance, Liu-Zhu Gong of the University of Science and Technology of China combined (Org. Lett. 2013, 15, 2676) 19, 20, and 21 to give the triester 22. Qi-Lin Zhou of Nankai University reduced (Angew. Chem. Int. Ed. 2013, 52, 6072) the tetrahydropyridine 23 to 24 in high ee. Takaaki Sato and Noritaka Chida of Keio University cyclized (Chem. Eur. J. 2013, 19, 678) the intermediate from reduction of 25 to the piperidine 26. Yasumasa Hamada of Chiba University devised (Tetrahedron Lett. 2013, 54, 1562) the rearrangement of 27 to the piperidine 28. In a synthesis of (–)-hippodamine, Shigeo Katsumura of Kwansei Gakuin University used (Org. Lett. 2013, 15, 2758) the chiral auxiliary 29 to direct the combination of 30 with 31 to give 32.

Carbocyclic Ring Construction: The Nicolaou Synthesis of Myceliothermophin E

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Claisen Rearrangement ◽  
Aldol Condensation ◽  
Crop Protection ◽  
Cope Rearrangement ◽  
Columbia University ◽  
Tetramic Acid ◽  
Ene Reaction ◽  
Ru Catalyst ◽  
Equilibrium Process ◽  
The University

Nan Zheng of the University of Arkansas developed (Adv. Synth. Catal. 2014, 356, 2831) a Ru catalyst for the addition of an amino cyclopropane 1 to an alkyne 2 to give 3. The reaction proceeded with high regiocontrol, but only modest stereocontrol. Alain De Mesmaeker of Syngenta Crop Protection, Switzerland found (Tetrahedron Lett. 2014, 55, 6577) that the β,γ-unsaturated amide 4 worked particularly well as a precursor to the keteniminium that cyclized to give, after hydrolysis, the cyclobuta­none 5. Baeyer–Villiger oxidation of 5 led to 5-deoxystrigol 6. David Tymann and Martin Hiersemann of the Technische Universität Dortmund have been exploring (Org. Lett. 2014, 16, 4062; Synthesis 2014, 46, 3110) the intra­molecular carbonyl ene reaction as a tool for the assembly of highly substituted cyclopentanes, as in the conversion of 7 to 8. On oxidation, 8 was readily carried on to the alkene 9. James L. Leighton of Columbia University conceived (J. Am. Chem. Soc. 2014, 136, 9878) the cascade transformation of 10 to 12. Deprotonation/silylation set the stage for Claisen rearrangement to give 11. The subsequent Cope rearrangement is an equilibrium process, driven by the ring strain of 11. K. C. Nicolaou of Rice University described (Angew. Chem. Int. Ed. 2014, 53, 10970) the total synthesis of the cytotoxic tetramic acid derivative myceliothermo­phin E 15. A key step in the synthesis was the intramolecular Michael addition/ aldol condensation that converted 13 to 14.

Stereocontrolled Construction of Arrays of Stereogenic Centers

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Aldol Condensation ◽  
Simple Procedure ◽  
Unsaturated Ester ◽  
Magnesium Bromide ◽  
National Chemical Laboratory ◽  
Chemical Laboratory ◽  
Enantiomerically Pure ◽  
Stereogenic Centers ◽  
Diastereoselective Addition ◽  
The University

Complex natural products and even some complex pharmaceuticals contain arrays of stereogenic centers. Sometimes, the desired array is readily available from a natural product, but usually, such arrays of multiple stereogenic centers must be assembled. Armando Córdova of Stockholm University has reported (Angew. Chem. Int. Ed. 2007, 46, 778) a simple procedure for the organocatalyst-mediated addition of the nitrene equivalent 2 to an α, β-unsaturated aldehyde to give the protected aziridine 4 in high ee. Organocatalysis was also used (Organic Lett. 2007, 9, 1001) by Arumugam Sudalai of the National Chemical Laboratory, Pune, to effect coupling of the aldehyde 5 with dibenzylazodicarboxylate 6 to give, following the List procedure, the intermediate aldehyde 7. Osmylation of the derived unsaturated ester 8 proceeded with high diastereocontrol, to give 9. Products 4 and 9 have adjacent stereogenic centers. Hisashi Yamamoto of the University of Chicago has introduced (J. Am. Chem. Soc. 2007, 129, 2762) the linchpin reagent acetaldehyde “super”silyl enol ether 11. Diastereoselective addition of 11 to the enantiomerically-pure aldehyde 10, with concomitant silyl transfer, followed by the addition of allyl magnesium bromide delivered the protected triol 12 in high de and ee. Arrays that combine alkylated and oxygenated or aminated centers are also important. Akio Kamimura of Yamaguchi University took (J. Org. Chem. 2007, 72, 3569) a Baylis- Hillman like approach, adding thiophenoxide to t -butyl acrylate in the presence of an enantiomerically-pure aldehyde N-sulfinimine such as 13 to give the adduct 14 with high diastereocontrol. Keiji Maruoka of Kyoto University has designed (Angew. Chem. Int. Ed. 2007, 46, 1738) the chiral amine 17, that catalyzed the condensation of an aldehyde with ethyl glyoxylate 16 with high enantiocontrol. In a very thoughtful approach, Liu-Zhu Gong of the University of Science and Technology of China in Hefei extended (Chem. Commun. 2007, 736) the now-classic aldol condensation of cyclohexanone to 4-substituted cyclohexanones such as 19. The product 21 could be carried in many directions, including to the Bayer-Villiger product 22. Arrays of alkylated and polyalkylated centers have been among the most challenging to prepare.

C–O Ring Construction: The Smith Synthesis of (+)-18-epi-Latrunculol A

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
New York ◽  
Gold Catalyst ◽  
Cyclic Ether ◽  
Oxidative Cyclization ◽  
Indian Institute ◽  
Chiral Auxiliary ◽  
Cancer Center ◽  
Columbia University ◽  
Institute Of Technology ◽  
The University

James A. Bull of Imperial College London showed (Angew. Chem. Int. Ed. 2014, 53, 14230) that the malonate 1 could readily be cyclized to the oxetane 2. Davide Ravelli of the University of Pavia functionalized (Adv. Synth. Catal. 2014, 356, 2781) the α position of the oxetane 3 with 4, leading to 5. Frank Glorius of the Westfälische Wilhelms-Universität Münster hydrogenated (Angew. Chem. Int. Ed. 2014, 53, 8751) the furan 6 to give 7 in high ee. Jia-Rong Chen and Wen-Jing Xiao of Central China Normal University converted (Eur. J. Org. Chem. 2014, 4714) the initial Henry adduct from 8 into the cyclic ether 9. Anil K. Saikia of the Indian Institute of Technology, Guwahati cyclized (J. Org. Chem. 2014, 79, 8592) the ene–yne 10 to the ketone 11. Richard C. D. Brown of the University of Southampton developed (Org. Lett. 2014, 16, 5104) a chiral auxiliary that effectively directed the oxidative cyclization of the diene 12 to 13. The chiral auxiliary could be recovered and reused. K. A. Woerpel of New York University showed (Org. Lett. 2014, 16, 3684) that, depending on the solvent, 15 could be added to 14 to give either 16 or 17. Samuel J. Danishefsky of Columbia University and the Memorial Sloan-Kettering Cancer Center also observed (Chem. Eur. J. 2014, 20, 8731) a marked solvent effect on the diastereoselectivity of the reduction of 18 to 19. Xiaoming Feng of Sichuan University added (Chem. Eur. J. 2014, 20, 14493) the ketone 20 to Danishefsky’s diene 21 to give 22 in high ee. Jhillu Singh Yadav of the Indian Institute of Chemical Technology effected (Tetrahedron Lett. 2014, 55, 3996) intramolecular opening of the oxetane of 23 to give, with clean inversion, the cyclic ether 24. Chun-Yu Ho of the South University of Science and Technology, taking advan­tage (J. Org. Chem. 2014, 79, 11873) of the superior chelating ability of the allyl ether, selectively cyclized 25 to 26. Xuegong She of Lanzhou University used (Angew. Chem. Int. Ed. 2014, 53, 10789) a gold catalyst to convert 27 into the eight-membered ring ether 28.

Alkaloid Synthesis: (–)-α-Kainic Acid (Cohen), Hyacinthacine A2 (Fox), (–)-Agelastatin A (Hamada), (+)-Luciduline (Barbe), (+)-Lunarine (Fan), (–)-Runanine (Herzon)

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Kainic Acid ◽  
Aldol Condensation ◽  
Catalyst System ◽  
Diels Alder ◽  
Yale University ◽  
University Of Pittsburgh ◽  
Agelastatin A ◽  
Alkaloid Synthesis ◽  
Carbocyclic Rings ◽  
The University

The intramolecular ene cyclization is still little used in organic synthesis. Theodore Cohen of the University of Pittsburgh trapped (J. Org. Chem. 2011, 76, 7912) the cyclization product from 1 with iodine to give 2, setting the stage for an enantiospecific total synthesis of (–)-α-kainic acid 3. Intramolecular alkene hydroamination has been effected with transition metal catalysts. Joseph M. Fox of the University of Delaware isomerized (Chem. Sci. 2011, 2, 2162) 4 to the trans cyclooctene 5 with high diastereocontrol. Deprotection of the amine led to spontaneous cyclization, again with high diastereocontrol to hyacinthacine A2 6. Yasumasa Hamada of Chiba University devised (Org. Lett. 2011, 13, 5744) a catalyst system for the enantioselective aziridination of cyclopentenone 7. The product 8 was carried on to the tricyclic alkaloid (–)-agelastatin A 9. Guillaume Barbe, now at Novartis in Cambridge, MA, effected (J. Org. Chem. 2011, 76, 5354) the enantioselective Diels-Alder cycloaddition of acrolein 11 to the dihydropyridine 10. Ring-opening ring-closing metathesis later formed one of the carbocyclic rings of (+)-luciduline 13, and set the stage for an intramolecular aldol condensation to form the other. Chun-An Fan of Lanzhou University employed (Angew. Chem. Int. Ed. 2011, 50, 8161) a Cinchona-derived catalyst for the enantioselective Michael addition to prepare 14. Although 14 and 15 were only prepared in 77% ee, crystallization to remove the racemic component of a later intermediate led to (+)-lunarine 16 in high ee. Seth B. Herzon of Yale University used (Angew. Chem. Int. Ed. 2011, 50, 8863) the enantioselective Diels-Alder addition with 18 to block one face of the quinone 17. Reduction of 19 followed by methylation delivered an iminium salt, only one face of which was open for the addition of an aryl acetylide. Thermolysis to remove the cyclopentadiene gave an intermediate that was carried on to (+)-runanine 20.

Arrays of Stereogenic Centers: The Barker Synthesis of (+)-Galbelgin

2015 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Chemistry ◽  
Indian Institute ◽  
Silver Catalyst ◽  
University Of Texas ◽  
Secondary Center ◽  
Stereogenic Centers ◽  
Enantioselective Epoxidation ◽  
Indian Institute Of Science ◽  
The University ◽  
Stereogenic Center

Gang Zhao of the Shanghai Institute of Organic Chemistry and Gang Zou of the East China University of Science and Technology devised (Adv. Synth. Catal. 2011, 353, 3129) an elegant catalyst for the direct enantioselective epoxidation of a simple acyclic enone 1. Ismail Ibrahem and Armando Córdova of Mid Sweden University and Stockholm University prepared (Adv. Synth. Catal. 2011, 353, 3114) 6 by combining three catalysts to effect the enantioselective addition of 5 to 4. Giovanni Casiraghi and Franca Zanardi of the Università degli Studi di Parma used (J. Org. Chem. 2011, 76, 10291) a silver catalyst to mediate the addition of 8 to 7 to give 9. Keiji Maruoka of Kyoto University condensed (Nature Chem. 2011, 3, 642) the diazo ester 10 with an aldehyde 4, leading, after reduction of the initial adduct and protection, to the diamine 11. Christoph Schneider of the Universität Leipzig effected (Synthesis 2011, 4050) the vinylogous addition of 13 to an imine 12, setting both stereogenic centers of 14. In the course of the coupling of 16 with the diol 15, Michael J. Krische of the University of Texas established (J. Am. Chem. Soc. 2011, 133, 12795) four new stereogenic centers. By adding (Chem. Commun. 2011, 47, 10557) an α-nitro ester 18 to the maleimide 19, Professor Maruoka established both the alkylated secondary center and the N-substituted quaternary center of 20. Srinivas Hotha of the Indian Institute of Science Education & Research and Torsten Linker of the University of Potsdam showed (Chem. Commun. 2011, 47, 10434) that the readily prepared lactone 21 could be opened to 23 without disturbing the stereogenic center adjacent to the carbonyls. Allan D. Headley and Bukuo Ni of Texas A&M University-Commerce devised (Synthesis 2011, 1993) a recyclable catalyst for the addition of an aldehyde 7 to a nitroalkene 24 in water to give 25. Alexandre Alexakis of the University of Geneva effected (Chem. Commun. 2011, 47, 7212) the triply convergent coupling of 26, 27, and 28 to give 29 as a single dominant diastereomer.

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