Alkene Metathesis: Synthesis of Panaxytriol (Lee), Isofagomine (Imahori and Takahata), Elatol (Stoltz), 5-F2t -Isoprostane (Snapper), and Ottelione B (Clive)

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Grignard Reagent ◽  
Conjugate Addition ◽  
Ring Closing Metathesis ◽  
University Of Illinois ◽  
Enantiomerically Pure ◽  
University Of Alberta ◽  
Cross Metathesis ◽  
Grubbs Catalysts ◽  
The University ◽  
First And Second Generation

Alkene metathesis has been used to prepare more and more challenging natural products. The first and second generation Grubbs catalysts 1 and 2 and the Hoveyda catalyst 3 are the most widely used. Daesung Lee of the University of Illinois at Chicago designed (Organic Lett. 2008, 10, 257) a clever chain-walking cross metathesis, combining 4 and 5 to make 6. The diyne 3 was carried on (3R, 9R, 10R )-Panaxytriol 7. Tatsushi Imahori and Hiroki Takahata of Tohoku Pharmaceutical University found (Tetrahedron Lett. 2008, 49, 265) that of the several derivatives investigated, the unprotected alcohol 8 cyclized most efficiently. Selective cleavage of the monosubstituted alkene followed by hydroboration delivered the alkaloid Isofagomine 10. Brian M. Stoltz of Caltech established (J. Am. Chem. Soc. 2008 , 130 , 810) the absolute configuration of the halogenated chamigrene Elatol 14 using the enantioselective enolate allylation that he had previously devised. A key feature of this synthesis was the stereocontrolled preparation of the cis bromohydrin. Marc L. Snapper of Boston College opened (J. Org. Chem. 2008, 73, 3754) the strained cyclobutene 15 with ethylene to give the diene 16. Remarkably, cross metathesis with 17 delivered 18 with high regioselectivity, setting the stage for the preparation of the 5-F2t - Isoprostane 19. Derrick L. J. Clive of the University of Alberta assembled (J. Org. Chem. 2008, 73, 3078) Ottelione B 26 from the enantiomerically-pure aldehyde 20. Conjugate addition of the Grignard reagent 21 derived from chloroprene gave the kinetic product 22, that was equilibrated to the more stable 23. Addition of vinyl Grignard followed by selective ring-closing metathesis then led to 26.

The Lee Synthesis of (−)-Crinipellin A

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Grignard Reagent ◽  
Conjugate Addition ◽  
Dipolar Cycloaddition ◽  
University Of Delaware ◽  
Initial Formation ◽  
Enantiomerically Pure ◽  
Silyl Enol Ether ◽  
Single Diastereomer ◽  
Sharpless Asymmetric Epoxidation ◽  
The University

The crinipellins are the only tetraquinane natural products. The enone crinipellins, including crinipellin A 3, have anticancer activity. Hee-Yoon Lee of the Korea Advanced Institute of Science and Technology (KAIST) envisioned (J. Am. Chem. Soc. 2014, 136, 10274) the assembly of 2 and thus 3 by the intramolecular dipolar cycloaddition of the diazoalkane derived from the tosylhydrazone 1. The initial cyclopentene was prepared from commercial 4 following the Williams procedure. Conjugate addition of the Grignard reagent 5 in the presence of TMS-Cl led to the silyl enol ether 6. Regeneration of the enolate followed by allylation gave 7. The preparation of the racemic ketone was completed by ozonolysis followed by selec­tive reduction and protection. Addition of hydride in an absolute sense led to separa­ble 1:1 mixture of diastereomers. Reoxidation of one of the diastereomers delivered enantiomerically enriched 8. A few steps later, after coupling with 10, the sidechain stereocenter was set by Sharpless asymmetric epoxidation. Oxidation of 11 gave the aldehyde, that was converted to the alkyne 12 by the Ohira protocol. Addition of the Grignard reagent 13 gave the allene 14 as an inconse­quential 1:1 mixture of diastereomers. Deprotection then led to the tosylhydrazone 1. The transformation of 1 to 2 proceeded by initial formation of the diazo alkane 15. Intramolecular dipolar cycloaddition gave 16, that lost N2 to give the trimethylene–methane diradical 17. The insertion into the distal alkene proceeded with remarkable stereocontrol, to give 2 as a single diastereomer—in 87% yield from 1. Direct α-hydroxylation of the ketone derived from 2 gave the wrong diastereo­mer, and hydride addition to 18 reduced the wrong ketone. As an alternative, the enantiomerically-pure sulfoximine anion was added to the more reactive ketone, and the product was reduced and protected to give 19. Allylic oxidation converted the alkene to the enone, and heating to reflux in toluene reversed the sulfoximine addi­tion, leading to 20. Epoxidation of 20 followed by α-methylenation delivered the enone 21, that proved to be particularly sensitive. Eventually, success was found with TASF. With a similarly sensitive substrate, Douglass F. Taber of the University of Delaware observed (J. Am. Chem. Soc. 1998, 120, 13285) that TBAF in THF buffered with solid NH4Cl worked well.

Advances in Alkene and Alkyne Metathesis

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Acetic Acid ◽  
Diels Alder ◽  
Alkyne Metathesis ◽  
Santa Barbara ◽  
Ring Closing Metathesis ◽  
Enol Ethers ◽  
Cross Metathesis ◽  
Simple Filtration ◽  
The University ◽  
Academy Of Sciences

As alkene metathesis is extended to more and more challenging substrates, improved catalysts and solvents are required. Robert H. Grubbs of Caltech developed (Organic Lett. 2008, 10, 441) the diisopropyl complex 1, that efficiently formed the trisubstituted alkene 6 by cross metathesis of 4 with 5. Hervé Clavier and Stephen P. Nolan of ICIQ, Tarragona, and Marc Mauduit of ENSC Rennes found (J. Org. Chem. 2008, 73, 4225) that after cyclization of 7 with the complex 2b, simple filtration of the reaction mixture through silica gel delivered the product 8 containing only 5.5 ppm Ru. The merit of CH2Cl2 as a solvent for alkene metathesis is that the catalysts (e.g. 1 - 3) are very stable. Claire S. Adjiman of Imperial College and Paul C. Taylor of the University of Warwick established (Chem. Commun. 2008, 2806) that although the second generation Grubbs catalyst 3 is not as stable in acetic acid, for the cyclization of 9 to 10 it is a much more active catalyst in acetic acid than in CH2Cl2 . Bruce H. Lipshutz of the University of California, Santa Barbara observed (Adv. Synth. Cat . 2008, 350, 953) that even water could serve as the reaction solvent for the challenging cyclization of 11 to 12, so long as the solubility- enhancing amphiphile PTS was included. Ernesto G. Mata of the Universidad Nacional de Rosario explored (J. Org. Chem. 2008, 73, 2024) resin isolation to optimize cross-metathesis, finding that the acrylate 13 worked particularly well. Karol Grela of the Polish Academy of Sciences, Warsaw optimized (Chem. Commun. 2008, 2468) cross-metathesis with a halogenated alkene 16. Jean-Marc Campagne of ENSC Montpellier extended (J. Am. Chem. Soc. 2008, 130, 1562) ring-closing metathesis to enynes such as 19. The product diene 20 was a reactive Diels-Alder dienophile. István E. Markó of the Université Catholique de Louvain applied (Tetrahedron Lett. 2008, 49, 1523) the known (OHL 20070122) ring-closing metathesis of enol ethers to the cyclization of the Tebbe product from 23. The ether 24 was oxidized directly to the lactone 25.

Other Methods for C–C Ring Construction: Pinolinone (Bach), Agelastatin A (Batey), Panaginsene (Lee), Salvileucalin D, Salvileucalin C (Ding), ent-Codeine (Hudlicky), Walsucochin B (Xie/Shi)

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Natural Product ◽  
Conjugate Addition ◽  
Chiral Medium ◽  
Relative Configuration ◽  
Enantiomerically Pure ◽  
Methyl Group ◽  
University Of Toronto ◽  
Agelastatin A ◽  
Cationic Cyclization ◽  
The University

Thorsten Bach of the Technische Universität München used (Chem. Commun. 2014, 50, 3353) the chiral medium-mediated photochemical 2+2 cycloaddition that he devel­oped to prepare 3 by combining 1 with 2. Oxidative cleavage led to (−)-pinolinone 4. Robert A. Batey of the University of Toronto rearranged (Angew. Chem. Int. Ed. 2013, 52, 10862) furfural 5 in the presence of 6 to give the enone 7. Acylation fol­lowed by intramolecular conjugate addition delivered agelastatin A 8. Hee-Yoon Lee of KAIST prepared (Org. Lett. 2014, 16, 2466) the tosylhydrazone Na salt 9 from citronellal. Thermolysis led, via a dialkyl diazo intermediate, to the tricy­clic 10. Direct comparison of synthetic material with the natural product panaginsene 11 enabled the assignment of the relative configuration of the pendant methyl group. Hanfeng Ding of Zhejiang University eliminated (Org. Lett. 2014, 16, 3376) HBr from 12 to give, after rearrangement, the cycloheptadiene salvileucalin D 13. Irradiation converted 13 to the cyclobutene salvileucalin C 14. In a recent chapter of his continuing work on the morphine alkaloids, Tomas Hudlicky of Brock University described (Adv. Synth. Catal. 2014, 356, 333) the intra­molecular [3+2] cycloaddition of the nitrone derived from 15 to give 16. This was readily carried on to ent-codeine 17. Xingang Xie and Xuegong She of Lanzhou University used (Org. Lett. 2014, 16, 1996) Shi epoxidation and Itsuno–Corey reduction to prepare 18 in enantiomerically-pure form. Cationic cyclization converted 18 to 19, that was oxidized to (−)-walsucochin B 20.

Metal-Mediated C–C Ring Construction: The Lei Synthesis of (−)-Huperzine Q

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Organic Chemistry ◽  
Conjugate Addition ◽  
Harvard University ◽  
Unsaturated Ester ◽  
Pd Catalyst ◽  
Enantiomerically Pure ◽  
Shanghai Institute ◽  
Diastereoselective Addition ◽  
University Of Bristol ◽  
The University

Following the Szymoniak protocol, Morwenna S. M. Pearson-Long and Philippe Bertus of the Université du Maine added (Synthesis 2015, 47, 992) the Grignard rea­gent 2 to the nitrile 1 to give the cyclopropyl amine 3. Chen-Guo Feng of the Shanghai Institute of Organic Chemistry prepared (Chem. Commun. 2015, 51, 8773) the cyclobutane 6 by enantioselective conjugate addition of 5 to the unsaturated ester 4. Martin Kotora of Charles University showed (Eur. J. Org. Chem. 2015, 2868) that the zirconacycle from the eneyne 7 reacted with the aldehyde 8 to give, after iodina­tion, the alcohol 9. Xiaoming Feng of Sichuan University used (Angew. Chem. Int. Ed. 2015, 54, 1608) a scandium catalyst to effect the intramolecular Roskamp cyclization of 10 to 11. Celia Dominguez of CHDI observed (Org. Lett. 2015, 17, 1401) that the double alkylation of the ester 12 with the dibromide 13 proceeded with high diaste­reoselectivity, to give 14. Hirokazu Tsukamoto of Tohoku University cyclized (Chem. Commun. 2015, 51, 8027) 15 to 16 in high ee. Daniel J. Weix of the University of Rochester found (J. Am. Chem. Soc. 2015, 137, 3237) that under the influence of an enantiomerically-pure Ti catalyst, the organon­ickel species derived from 18 opened the prochiral epoxide 17 to give 19 in high ee. John F. Bower of the University of Bristol optimized (J. Am. Chem. Soc. 2015, 137, 463) conditions for the highly diastereoselective Rh-mediated cyclocarbonylation of 20 to 21. Margaret A. Brimble of the University of Auckland initiated (J. Org. Chem. 2015, 80, 2231) the construction of the cyclohexenone 24 by the diastereoselective addition of 23 to the unsaturated ester 22. Olivier Baslé and Marc Maduit of ENSC Rennes devised (Chem. Eur. J. 2015, 21, 993) conditions for the preparation of 26 by enantioselective conjugate addition to the cyclohexenone 25. Yoshito Kishi of Harvard University demonstrated (Tetrahedron Lett. 2015, 56, 3220) that the carbenoid generated from the epoxide 27 cyclized to 28 with high dia­stereoselectivity. Wenjun Tang, also of the Shanghai Institute of Organic Chemistry, developed (Angew. Chem. Int. Ed. 2015, 54, 3033) a Pd catalyst for the diastereoselec­tive (because it is enantioselective) cyclization of 29 to 30.

Construction of Oxygenated and Aminated Stereogenic Centers

2013 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Conjugate Addition ◽  
Indiana University ◽  
University Of Alberta ◽  
University Of Toronto ◽  
Stereogenic Centers ◽  
University Of Calgary ◽  
Cu Catalyst ◽  
Korea Research Institute ◽  
Hydrolysis Of Esters ◽  
The University

Computational analysis of the Novozyme 435 active site led (Tetrahedron Lett. 2010, 51, 309) Liyan Dai and Hongwei Yu of Zhejiang University, Hangzhou, to t-butanol for the enantioselective monoesterification of 1 to 2. Bruce H. Lipshutz of the University of California, Santa Barbara, devised (J. Am. Chem. Soc. 2010, 132, 7852) a Cu catalyst that mediated the enantioselective 1,2-reduction of α-branched enones such as 3. Qi-Lin Zhou of Nankai University found (J. Am. Chem. Soc. 2010, 132, 1172) that an α-alkoxy unsaturated acid 5 could be hydrogenated with high ee. Tohru Yamada of Keio University desymmetrized (J. Am. Chem. Soc. 2010, 132, 4072) the tertiary alcohol 7, delivering the enol lactone 8. Zachary D. Aron of Indiana University established (Organic Lett. 2010, 12, 1916) that the simple aldehyde 10 effected rapid racemization of the α-amino ester 9. Running the epimerization in the presence of an enantioselective esterase produced 11 high ee. Robert A. Batey of the University of Toronto devised (Organic Lett. 2010, 12, 260) a Pd catalyst for the enantioselective rearrangement of 12 to 13. In the course of a synthesis of dapoxetine, Hyeon-Kyu Lee of the Korea Research Institute of Chemical Technology showed (J. Org. Chem. 2010, 75, 237) that the Rh*-mediated intramolecular C-H insertion of 14 to 15, as developed by Du Bois, gave the opposite absolute configuration to that originally assigned. To prepare α-quaternary amines, Thomas G. Back of the University of Calgary explored (J. Org. Chem. 2010, 75, 1612) the selectivity of the PLE hydrolysis of esters such as 16. Daniel R. Fandrick and colleagues at Boehringer Ingelheim reported (J. Am. Chem. Soc. 2010, 132, 7600) a general method for the catalytic enantioselective propargylation of aldehydes, including 18. Dennis G. Hall of the University of Alberta devised (J. Am. Chem. Soc. 2010, 132, 5544) a route to α-hydroxy esters such as 22 by enantioselective conjugate addition to 21. Alexandre Alexakis of the University of Geneva prepared (Chem. Commun. 2010, 46, 4085) disubstituted epoxides such as 25 by the conjugate addition of 23 to 24.

The Kozmin Synthesis of Spirofungin A

2011 ◽  
Author(s):  
Douglass Taber
Keyword(s):  
Absolute Configuration ◽  
Journal Article ◽  
Ring System ◽  
Spatial Proximity ◽  
Silyl Ether ◽  
Secondary Alcohols ◽  
Ring Closing Metathesis ◽  
Cross Metathesis ◽  
The University ◽  
Flexible Ring

Often, 6,6-spiroketals such as Spirofungin A 3 have a strong anomeric bias. Spirofungin A does not, as the epimer favored by double anomeric stabilization suffers from destabilizing steric interactions. In his synthesis of 3, Sergey A. Kozmin of the University of Chicago took advantage (Angew. Chem. Int. Ed. 2007, 46, 8854) of the normally-destablizing spatial proximity of the two alkyl branches of 3, joining them with a siloxy linker to assure the anomeric preference of the spiroketal. The assembly of 1 showcased the power of asymmetric crotylation, and of Professor Kozmin’s linchpin cyclopropenone ketal cross metathesis. To achieve the syn relative (and absolute) configuration of 6, commercial cis-2-butene was metalated, then condensed with the Brown (+)-MeOB(Ipc)2 auxiliary. The accompanying Supporting Information, accessible via the online HTML version of the journal article, includes a succinct but detailed procedure for carrying out this homologation. For the anti relative (and absolute) configuration of 9, it is more convenient to use the tartrate 8 introduced by Roush. Driven by the release of the ring strain inherent in 10, ring opening cross metathesis with 6 proceeded to give the 1:1 adduct 11 in near quantitative yield. The derived cross-linked silyl ether 12 underwent smooth ring-closing metathesis to the dienone 1. On hydogenation, the now-flexible ring system could fold into the spiro ketal. With the primary and secondary alcohols bridged by the linking silyl ether, only one anomeric form, 2, of the spiro ketal was energetically accessible. A remaining challenge was the stereocontrolled construction of the trisubstituted alkene. To this end, the aldehyde 13 was homologated to the dibromide 14. Pd-mediated coupling of the alkenyl stannane 15 with 14 was selective for the E bromide. The residual Z bromide was then coupled with Zn(CH3)2 to give 16. These steps, and the final steps to complete the construction of spirofungin A 3 , could be carried out without exposure to equilibrating acid, so the carefully established spiro ketal confi guration was maintained.

Diversity-oriented synthesis of enantiopure N-protected β,β-dialkylserines

2004 ◽  
Vol 82 (2) ◽  
pp. 318-324 ◽  
Author(s):  
James E Dettwiler ◽  
William D Lubell
Keyword(s):  
Amino Acid ◽  
Methyl Ester ◽  
Grignard Reagent ◽  
Primary Alcohol ◽  
Sodium Chlorite ◽  
Ring Closing Metathesis ◽  
Diversity Oriented Synthesis ◽  
Enantiomerically Pure ◽  
Catalysed Oxidation

A series of enantiomerically pure N-Boc-protected β,β-dialkylserines was synthesized by addition of the appropriate Grignard reagent to N-(Boc)serine methyl ester, followed by TEMPO-catalysed oxidation of the primary alcohol with sodium chlorite and sodium hypochlorite.Key words: amino acid, serine, β,β-dialkylserines, ring-closing metathesis.

scholarly journals C-Glycosidic Genistein Conjugates and Their Antiproliferative Activity

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Aleksandra Rusin ◽  
Maciej Chrubasik ◽  
Katarzyna Papaj ◽  
Grzegorz Grynkiewicz ◽  
Wiesław Szeja
Keyword(s):  
Cell Cycle ◽  
Culture Medium ◽  
Parent Compound ◽  
Metathesis Reaction ◽  
Cross Metathesis ◽  
Grubbs Catalysts ◽  
M Phase ◽  
First And Second Generation ◽  
Antiproliferative Activities

This paper presents our attempt to investigate scopes and the limitations of olefin cross-metathesis (CM) reaction in the synthesis of complex C-glycosides of genistein and evaluation of their antiproliferative activities. Novel genistein glycoconjugates were synthesized with the utility of CM reaction initiated by first and second generation of Grubbs catalysts. The relative reactivity of utilized olefins, based on categories proposed by Grubbs, was estimated.In vitroexperiments in cancer cell lines showed that the selected derivatives (3aand3f) exhibited higher antiproliferative potential than the parent compound, genistein, and were able to block the cell cycle in the G2/M phase. The observed mechanism of action of C-glycosidic derivatives was similar to the activity of their O-glycosidic counterparts. These compounds were stable in culture medium. The obtained results show that our approach to genistein modification with application of cross-metathesis reaction allowed to obtain stable glycoconjugates with improved anticancer potential, compared to the parent isoflavone.

The Smith Synthesis of (−)-Nodulisporic Acid D

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Functional Group ◽  
University Of Pennsylvania ◽  
Magnesium Bromide ◽  
Ring Closing Metathesis ◽  
Enantiomerically Pure ◽  
Model Study ◽  
Silyl Enol Ether ◽  
Robinson Annulation ◽  
The University ◽  
Stereogenic Center

The nodulisporic acids, isolated from the endophytic fungus Nodulisporium sp., show promising insecticidal activity. Amos B. Smith III of the University of Pennsylvania envisioned (J. Am. Chem. Soc. 2015, 137, 7095) the construction of the central indole of nodulisporic acid D 4 by the convergent coupling of the chloroaniline 1 with the enol triflate 2. The preparation of 2 began (Org. Process Res. Dev. 2007, 11, 19) with the mono­ketal 5 of the Wieland–Miescher ketone, available in enantiomerically-pure form by organocatalyzed Robinson annulation. Condensation with thiophenol and formal­dehyde gave 6, which, under dissolving metal conditions, was reduced to an enolate that was trapped as the silyl enol ether 7. Condensation again with formaldehyde gave 8, that was converted by reduction and protecting group exchange to the ketone 9. Pd-catalyzed formylation of the derived enol triflate led to 10. The Cu-meditated conjugate addition of vinyl magnesium bromide to the unsatu­rated aldehyde 10 was carefully optimized to maximize equatorial addition, away from the angular methyl group. Subsequent C-methylation of the aldehyde was achieved by generating the Li enolate and carrying out the alkylation in diglyme. With 11 in hand, the third carbocyclic ring was assembled by 1,2-addition of vinylmagnesium bromide to the aldehyde followed by ring-closing metathesis and oxidation to give 12. Hydrogenation followed by functional group interconversion then completed the assembly of the enol triflate 2. The stereogenic center of 1 was established by Enders alkylation of 13 with the iodide 14. The ketone 15 was best liberated by ozonolysis under non-epimerizing conditions. The critical Barluenga indole construction that formed 3 also required careful optimization in a model study, the key observation being the value of the Buchwald ligand RuPhos. The conditions developed were found, remarkably, to be compatible with the aldehyde functional group, so subsequent Horner–Wadsworth–Emmons condensation with 16 could be carried out directly, to complete the synthe­sis of (−)-nodulisporic acid D 4.

Arrays of Stereogenic Centers: The Shin/Chandrasekhar Synthesis of (+)-Lactacystin

2017 ◽  
Author(s):  
Douglass F. Taber
Keyword(s):  
Major Product ◽  
South Florida ◽  
Allylic Alcohol ◽  
Israel Institute ◽  
University Of Illinois ◽  
Enantiomerically Pure ◽  
Boston College ◽  
Stereogenic Centers ◽  
Institute Of Technology ◽  
The University

Kami L. Hull of the University of Illinois established (J. Am. Chem. Soc. 2014, 136, 11256) conditions for the diastereoselective hydroamination of 1 with 2 to give 3. Jon C. Antilla of the University of South Florida employed (Org. Lett. 2014, 16, 5548) an enantiomerically-pure Li phosphate to direct the opening of the prochiral epoxide 4 to 5. Jordi Bujons and Pere Clapés of IQAC-CSIC engineered (Chem. Eur. J. 2014, 20, 12572) an enzyme that mediated the enantioselective addition of glycolaldehyde 7 to an aldehyde 6, leading to 8. Takahiro Nishimura of Kyoto University set (J. Am. Chem. Soc. 2014, 136, 9284) the two stereogenic centers of 11 by adding 10 to the diene 9. Amir H. Hoveyda of Boston College added (J. Am. Chem. Soc. 2014, 136, 11304) the propargylic anion derived from 13 to the aldehyde 12 to give, after oxida­tion, the diol 14. Yujiro Hayashi of Tohoku University constructed (Adv. Synth. Catal. 2014, 356, 3106) 17 by the combination of 15 with 16. Yitzhak Apeloig and Ilan Marek of Technion-Israel Institute of Technology prepared (J. Org. Chem. 2014, 79, 12122) the bromo diol 20 by rearranging the adduct between the alkyne 19 and the acyl silane 18. James P. Morken, also of Boston College, effected (J. Am. Chem. Soc. 2014, 136, 17918) enantioselective coupling of 22 with the bis-borane 21. The prod­uct allyl borane added to benzaldehyde to give the alcohol 23. Sentaro Okamoto of Kanagawa University reduced (Org. Lett. 2014, 16, 6278) the aryl oxetane 24 to an intermediate that coupled with allyl bromide to give the alco­hol 25. In the presence of catalytic CuCN, the alternative diastereomer was the major product. Erick M. Carreira of ETH Zürich used (Angew. Chem. Int. Ed. 2014, 53, 13898) a combination of an Ir catalyst and an organocatalyst to couple the aldehyde 27 with the allylic alcohol 26. The four possible combinations of enantiomerically pure catalysts worked equally well, enabling the preparation of each of the four enan­tiomerically pure diastereomers of 28.

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