Best Synthetic Methods: Functional Group Transformation

Author(s):  
Douglass Taber

François Morvan of the Université de Montpellier, using the inexpensive dimethyl phosphite, optimized (Tetrahedron Lett. 2008, 49, 3288) the free radical reduction of 1 to 2. Pawan K. Sharma of Kurukshetra University found (Tetrahedron Lett. 2008, 48, 8704) that NaBH4 in the presence of a catalytic amount of RuCl3.xH2 O reduced monosubstituted and disubstituted alkenes, such as 3, to the corresponding alkanes. Note that benzyl ethers were stable to these conditions. Ken Suzuki of Asahi Kasei Chemicals and Shun-Ichi Murahashi of Okayama University of Science established conditions (Angew. Chem. Int. Ed. 2008, 47, 2079) for the oxidation of primary amines such as 5 to oximes. Both ketoximes such as 6 and aldoximes were prepared using this protocol. Primary and secondary alcohols were stable to these conditions. Three noteworthy procedures for the oxidation of an aldehyde to the acid oxidation state were recently reported. Jonathan M. J. Williams of the University of Bath demonstrated (Chem. Commun. 2008, 624) that crotonitrile could serve as the hydrogen acceptor in the oxidation of an aldehyde 7 to the methyl ester 8. Note that isolated alkenes were stable to these conditions. Vikas N. Telvekar the University Institute of Chemical Technology, Mumbai improved (Tetrahedron Lett . 2008, 49, 2213) the oxidative amination of an aldehyde 9 to the nitrile 10. G. Sekar of the Indian Institute of Technology Madras effected (Tetrahedron Lett. 2008, 49, 1083) oxidation of an aldehyde 11 to the acid 12, under conditions that would be expected to not oxidize a primary or secondary alcohol. J. S. Yadav of the Indian Institute of Chemical Technology, Hyderabad observed (Tetrahedron Lett. 2008, 49, 3015) that the activation of a thiophenol 14 with N-chlorosuccimide generated a species that added regioselectively to a ketone 13 to give the thioether 15. Oxidation of the sulfide 15 followed by heating of the resulting sulfoxide would give the enone 16. This appears to be an easily scalable procedure. It is well known that an acid 17 and an amine 18 will condense at elevated temperature to give the amide 20.

Author(s):  
Douglass Taber

Although methods both for reduction and for oxidation are well developed, there is always room for improvement. While ketones are usually reduced using metal hydrides, hydrogen gas is much less expensive on scale. Charles P. Casey of the University of Wisconsin has devised (J. Am. Chem. Soc. 2007, 129, 5816) an Fe-based catalyst that effects the transformation of 1 to 2. Note that the usually very reactive monosubstituted alkene is not reduced and does not migrate. Takeshi Oriyama of Ibaraki University has developed a catalyst, also Fe-based (Chemistry Lett. 2007, 38) for reducing aldehydes to ethers. Using this approach, an alcohol such as 3 can be converted into a variety of substituted benzyl ethers, including 5. Simple aliphatic aldehydes and alcohols also work well. Oxidation of alcohols to aldehydes or ketones is one of the most common of organic transformations. Several new processes catalytic in metal have been put forward. Tharmalingam Punniyamurthy of the Indian Institute of Technology, Guwahati has found (Adv. Synth. Cat. 2007, 349, 846) that catalytic V(IV) oxide on silica gel, stirred with t-butyl hydroperoxide in t-butyl alcohol at room temperature smoothly oxidized 6 to 7. After the reaction, the catalyst was separated by filtration. Another carbonyl can also serve as the hydride acceptor, but then the transfer can be reversible. Jonathan M. J. Williams of the University of Bath has shown (Tetrahedron Lett. 2007, 48, 3639) that with a Ru catalyst, methyl levulinate 9 could serve as the hydride acceptor, with the byproduct alcohol being drained off as the lactone 11. Hansjörg Grützmacher of the ETH Zürich developed an Ir catalyst (Angew. Chem. Int. Ed. 2007, 46, 3567) with benzoquinone as the net oxidant. that showed marked preference for the oxidation of primary over secondary alcohols. Yasuhiro Uozumi of the Institute for Molecular Science, Aichi, has devised (Angew. Chem. Int. Ed . 2007, 46, 704) a nanoencapsulated Pt catalyst that worked well with O2 or even with air. The catalyst was easily separated from the product, and maintained its activity over several cycles.


2021 ◽  
Author(s):  
Roger Few ◽  
Mythili Madhavan ◽  
Narayanan N.C. ◽  
Kaniska Singh ◽  
Hazel Marsh ◽  
...  

This document is an output from the “Voices After Disaster: narratives and representation following the Kerala floods of August 2018” project supported by the University of East Anglia (UEA)’s GCRF QR funds. The project is carried out by researchers at UEA, the Indian Institute for Human Settlements (IIHS), the Indian Institute of Technology (IIT), Bombay, and Canalpy, Kerala. In this briefing, we provide an overview of some of the emerging narratives of recovery in Kerala and discuss their significance for post-disaster recovery policy and practice. A key part of the work was a review of reported recovery activities by government and NGOs, as well as accounts and reports of the disaster and subsequent activities in the media and other information sources. This was complemented by fieldwork on the ground in two districts, in which the teams conducted a total of 105 interviews and group discussions with a range of community members and other local stakeholders. We worked in Alleppey district, in the low-lying Kuttanad region, where extreme accumulation of floodwaters had been far in excess of the normal seasonal levels, and in Wayanad district, in the Western Ghats, where there had been a concentration of severe flash floods and landslides.


Author(s):  
Douglass F. Taber

Fung-E Hong of the National Chung Hsing University devised (Adv. Synth. Catal. 2011, 353, 1491) a protocol for the oxidative cleavage of an alkene 1 (or an alkyne) to the carboxylic acid 2. Patrick H. Dussault of the University of Nebraska found (Synthesis 2011, 3475) that Na triacetoxyborohydride reduced the methoxy hydroperoxide from the ozonolysis of 3 to the aldehyde 4. Reductive amination of 4 can be effected in the same pot with the same reagent. Philippe Renaud of the University of Bern used (J. Am. Chem. Soc. 2011, 133, 5913) air to promote the free radical reduction to 6 of the intermediate from the hydroboration of 5. Robert H. Grubbs of Caltech showed (Org. Lett. 2011, 13, 6429) that the phosphonium tetrafluoroborate 8 prepared by hydrophosphonation of 7 could be used directly in a subsequent Wittig reaction. Dominique Agustin of the Université de Toulouse epoxidized (Adv. Synth. Catal. 2011, 353, 2910) the alkene 9 to 10 without solvent other than the commercial aqueous t-butyl hydroperoxide. Justin M. Notestein of Northwestern University effected (J. Am. Chem. Soc. 2011, 133, 18684) cis dihydroxylation of 9 to 11 using 30% aqueous hydrogen peroxide. Chi-Ming Che of the University of Hong Kong devised (Chem. Commun. 2011, 47, 10963) a protocol for the anti-Markownikov oxidation of an alkene 12 to the aldehyde 13. Aziridines such as 14 are readily prepared from alkenes. Jeremy B. Morgan of the University of North Carolina Wilmington uncovered (Org. Lett. 2011, 13, 5444) a catalyst that rearranged 14 to the protected amino alcohol 15. A monosubstituted alkene 16 is particularly reactive both with free radicals and with coordinately unsaturated metal centers. A variety of transformations of monosubstituted alkenes have been reported. Nobuharu Iwasawa of the Tokyo Institute of Technology employed (J. Am. Chem. Soc. 2011, 133, 12980) a Pd pincer complex to catalyze the oxidative monoborylation of 16 to give 17. The 1,1-bis boryl derivatives could also be prepared. Professor Renaud effected (J. Am. Chem. Soc. 2011, 133, 13890) radical addition to 16 leading to the terminal azide 18.


Author(s):  
Douglass F. Taber

Kyungsoo Oh of Chung-Ang University cyclized (Org. Lett. 2015, 17, 450) the chloro enone 1 with NBS to the furan 2. Hongwei Zhou of Zhejiang University acylated (Adv. Synth. Catal. 2015, 357, 389) the imine 3, leading to the furan 4. H. Surya Prakash Rao of Pondicherry University found (Synlett 2014, 26, 1059) that under Blaise conditions, exposure of 5 to three equivalents of 6 led to the pyrrole 7. Yoshiaki Nishibayashi of the University of Tokyo and Yoshihiro Miyake, now at Nagoya University, prepared (Chem. Commun. 2014, 50, 8900) the pyrrole 10 by adding the silane 9 to the enone 8. Barry M. Trost of Stanford University developed (Org. Lett. 2015, 17, 1433) the phosphine-mediated cyclization of 11 to an intermediate that on brief exposure to a Pd catalyst was converted to the pyridine 12. Nagatoshi Nishiwaki of the Kochi University of Technology added (Chem. Lett. 2015, 44, 776) the dinitrolactam 14 to the enone 13 to give the pyridine 15. Metin Balci of the Middle East Technical University assembled (Org. Lett. 2015, 17, 964) the tricyclic pyridine 18 by adding propargyl amine 17 to the aldehyde 16. Chada Raji Reddy of the Indian Institute of Chemical Technology cyclized (Org. Lett. 2015, 17, 896) the azido enyne 19 to the pyridine 20 by simple exposure to I2. Björn C. G. Söderberg of West Virginia University used (J. Org. Chem. 2015, 80, 4783) a Pd catalyst to simultaneously reduce and cyclize 21 to the indole 22. Ranjan Jana of the Indian Institute of Chemical Biology effected (Org. Lett. 2015, 17, 672) sequential ortho C–H activation and cyclization, adding 23 to 24 to give the 2-substituted indole 25. In a complementary approach, Debabrata Maiti of the Indian Institute of Technology Bombay added (Chem. Eur. J. 2015, 21, 8723) 27 to 26 to give the 3-substituted indole 28. In a Type 8 construction, Nobutaka Fujii and Hiroaki Ohno of Kyoto University employed (Chem. Eur. J. 2015, 21, 1463) a gold catalyst to add 30 to 29, leading to 31.


Author(s):  
Douglass F. Taber

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.


Author(s):  
Douglass F. Taber

The catalytic reduction of the alkene 1 gave the cis-fused product (not illustrated), by kinetic H₂ addition to the less congested face of the alkene. Ryan A. Shenvi of Scripps La Jolla found (J. Am. Chem. Soc. 2014, 136, 1300) conditions for stepwise HAT, con­verting 1 to the thermodynamically-favored trans-fused ketone 2. Seth B. Herzon of Yale University devised (J. Am. Chem. Soc. 2014, 136, 6884) a protocol for the reduc­tion, mediated by 4, of the double bond of a haloalkene 3 to give the saturated halide 5. The Shenvi conditions also reduced a haloalkene to the saturated halide. Daniel J. Weix of the University of Rochester and Patrick L. Holland, also of Yale University, established (J. Am. Chem. Soc. 2014, 136, 945) conditions for the kinetic isomerization of a terminal alkene 6 to the Z internal alkene 7. Christoforos G. Kokotos of the University of Athens showed (J. Org. Chem. 2014, 79, 4270) that the ketone 9, used catalytically, markedly accelerated the Payne epoxidation of 8 to 10. Note that Helena M. C. Ferraz of the Universidade of São Paulo reported (Tetrahedron Lett. 2000, 41, 5021) several years ago that alkene epoxidation was also easily carried out with DMDO generated in situ from acetone and oxone. Theodore A. Betley of Harvard University prepared (Chem. Sci. 2014, 5, 1526) the allylic amine 12 by reacting the alkene 11 with 1-azidoadamantane in the presence of an iron catalyst. Rodney A. Fernandes of the Indian Institute of Technology Bombay developed (J. Org. Chem. 2014, 79, 5787) efficient conditions for the Wacker oxida­tion of a terminal alkene 6 to the methyl ketone 13. Yong-Qiang Wang of Northwest University oxidized (Org. Lett. 2014, 16, 1610) the alkene 6 to the enone 14. Peili Teo of the National University of Singapore devised (Chem. Commun. 2014, 50, 2608) conditions for the Markovnikov hydration of the alkene 6 to the alcohol 15. Internal alkenes were inert under these conditions, but Yoshikazo Kitano of the Tokyo University of Agriculture and Technology effected (Synthesis 2014, 46, 1455) the Markovnikov amination (not illustrated) of more highly substituted alkenes.


Author(s):  
Douglass F. Taber

D. Srinivasa Reddy of the National Chemical Laboratory converted (Org. Lett. 2015, 17, 2090) the selenide 1 to the alkene 2 under ozonolysis conditions. Takamitsu Hosoya of the Tokyo Medical and Dental University found (Chem. Commun. 2015, 51, 8745) that even highly strained alkynes such as 4 can be generated from a sulfinyl vinyl triflate 3. An alkyne can be protected as the dicobalt hexacarbonyl complex. Joe B. Gilroy and Mark S. Workentin of the University of Western Ontario found (Chem. Commun. 2015, 51, 6647) that following click chemistry on a non-protected distal alkyne, deprotection of 5 to 6 could be effected by exposure to TMNO. Stefan Bräse of the Karlsruhe Institute of Technology and Irina A. Balova of Saint Petersburg State University showed (J. Org. Chem. 2015, 80, 5546) that the bend of the Co complex of 7 enabled ring-closing metathesis, leading after deprotection to 8. Morten Meldal of the University of Copenhagen devised (Eur. J. Org. Chem. 2015, 1433) 9, the base-labile protected form of the aldehyde 10. Nicholas Gathergood of Dublin City University and Stephen J. Connon of the University of Dublin developed (Eur. J. Org. Chem. 2015, 188) an imidazolium catalyst for the exchange deprotection of 11 to 13, with the inexpensive aldehyde 12 as the acceptor. Peter J. Lindsay-Scott of Eli Lilly demonstrated (Org. Lett. 2015, 17, 476) that on exposure to KF, the isoxa­zole 14 unraveled to the nitrile 15. Masato Kitamura of Nagoya University observed (Tetrahedron 2015, 71, 6559) that the allyl ester of 16 could be removed to give 17, with the other alkene not affected. Benzyl ethers are among the most common of alcohol protecting groups. Yongxiang Liu and Maosheng Cheng of Shenyang Pharmaceutical University showed (Adv. Synth. Catal. 2015, 357, 1029) that 18 could be converted to 19 simply by expo­sure to benzyl alcohol in the presence of a gold catalyst. Reko Leino of Åbo Akademi University developed (Synthesis 2015, 47, 1749) an iron catalyst for the reductive benzylation of 20 to 21. Related results (not illustrated) were reported (Org. Lett. 2015, 17, 1778) by Chae S. Yi of Marquette University.


Author(s):  
Douglass F. Taber

Gojko Lalic of the University of Washington developed (Angew. Chem. Int. Ed. 2014, 53, 6473) conditions for the preparation of the fluoride 2 by SN2 displacement of the triflate 1. Ross M. Denton of the University of Nottingham showed (Tetrahedron Lett. 2014, 55, 799) that a polymer-bound phosphine oxide activated with oxalyl bromide would convert an alcohol 3 to the bromide 4. The polymer could be filtered off and reactivated directly. Jonas C. Peters and Gregory C. Fu of Caltech devised (J. Am. Chem. Soc. 2014, 136, 2162) a photochemically-activated Cu catalyst that mediated the displacement of the bromide 5 by the amide 6 to give 7. Mark L. Trudell of the University of New Orleans used (Synthesis 2014, 46, 230) an Ir catalyst to couple the amide 9 with the alcohol 8, leading to 10. Tohru Fukuyama of Nagoya University converted (Org. Lett. 2014, 16, 727) the unsaturated aldehyde 11 into the ester 12. As the transformation proceeded via proton­ation of the enolized acyl cyanide, the less stable diastereomer was formed kinetically. Brindaban C. Ranu of the Indian Association for the Cultivation of Science developed (Org. Lett. 2014, 16, 1040) conditions for the coupling of an alkenyl halide 13 with a phenol, leading to the vinyl ether 14. Inter alia, this would be a convenient way to hydrolyze an alkenyl halide to the aldehyde. Vinyl ethers can also be oxidized directly to the ester, and to the unsaturated aldehyde. Pallavi Sharma and John E. Moses of the University of Lincoln observed (Org. Lett. 2014, 16, 2158) that the cyanation of the alkenyl halide 15 delivered 16, with retention of the geometry of the alkene. Jitendra K. Bera of the Indian Institute of Technology Kanpur uncovered (Tetrahedron Lett. 2014, 55, 1444) “on water” conditions for the hydrolysis of a terminal alkyne 17 to the methyl ketone 18. Jiannan Xiang and Weimin He of Hunan University prepared (Eur. J. Org. Chem. 2014, 2668) the keto phosphonate 20 by hydrolysis of the alkynyl phosphonate 19. Ken-ichi Fujita of the National Institute of Advanced Industrial Science and Technology cyclized (Tetrahedron Lett. 2014, 55, 3013) the alkyne 21 with CO₂, leading to 22.


Author(s):  
Douglass F. Taber

The fungal secondary metabolite (+)-pleuromutilin 3 exerts antibiotic activity by binding to the prokaryotic ribosome. Semisynthetic derivatives of 3 are used clinically. The central step of the first synthesis of (+)-pleuromutilin 3, devised (Chem. Eur. J. 2013, 19, 6718) by David J. Procter of the University of Manchester, was the SmI2-mediated reductive closure of 1 to the tricyclic 2. The starting material for the synthesis was the inexpensive dihydrocarvone 4. Ozonolysis and oxidative fragmentation following the White protocol delivered 5 in high ee. Conjugate addition with 6 followed by Pd-mediated oxidation of the resulting silyl enol ether gave the enone 7. Subsequent conjugate addition of 8 proceeded with modest but useful diastereoselectivity to give an enolate that was trapped as the triflate 9. The Sakurai addition of the derived ester 10 with 11 led to 12 and so 1 as an inconsequential 1:1 mixture of diastereomers. The SmI2-mediated cyclization of 1 proceeded with remarkable diastereocontrol to give 2. SmI2 is a one-electron reductant that is also a Lewis acid. It seems likely that one SmI2 bound to the ester and the second to the aldehyde. Electron transfer then led to the formation of the cis-fused five-membered ring, with the newly formed alkoxy constrained to be exo to maintain contact with the complexing Sm. Intramolecular aldol condensation of the resulting Sm enolate with the other aldehyde then formed the six-membered ring, with the alkoxy group again constrained by association with the Sm. Hydrogenation of 13 gave 14, which could be brought to diastereomeric purity by chromatography. Elegantly, protection of the ketone simultaneously selectively deprotected one of the two silyl ethers, thus differentiating the two secondary alcohols. Reduction of the ester to the primary alcohol then delivered the diol 15. Selective esterification of the secondary alcohol followed by thioimidazolide formation and free radical reduction completed the preparation of 16. Ketone deprotection followed by silyl ether formation and Rubottom oxidation led to the diol 17. Protection followed by the addition of 18 and subsequent hydrolysis and reduction gave the allylic alcohol 19.


Author(s):  
Douglass F. Taber

Sisir K. Mandal of Asian Paints R&T Centre, Mumbai used (Tetrahedron Lett. 2013, 54, 530) a Ru catalyst to couple 2 with an electron-rich arene 1 to give 3. Jun-ichi Yoshida of Kyoto University (J. Am. Chem. Soc. 2013, 135, 5000) and John F. Hartwig of the University of California, Berkeley (J. Am. Chem. Soc. 2013, 135, 8480) also reported direct amination protocols. Tommaso Marcelli of the Politecnico di Milano and Michael J. Ingleson of the University of Manchester effected (J. Am. Chem. Soc. 2013, 135, 474) the electrophilic borylation of the aniline 4 to give 5. The regioselectivity of Ir-catalyzed borylation (J. Am. Chem. Soc. 2013, 135, 7572; Org. Lett. 2013, 15, 140) is complementary to the electrophilic process. Professor Hartwig carried (Angew. Chem. Int. Ed. 2013, 52, 933) the borylated product from 6 onto Ni-mediated coupling to give the alkylated product 7. Weiping Su of the Fujian Institute of Research on the Structure of Matter devised (Org. Lett. 2013, 15, 1718) an intriguing Pd-mediated oxidative coupling of nitroethane 9 with 8 to give 10. The coupling is apparently not proceeding via nitroethylene. Peiming Gu of Ningxia University developed (Org. Lett. 2013, 15, 1124) an azide-based cleavage that converted the aldehyde 11 into the formamide 13. Zhong-Quan Liu of Lanzhou University showed (Tetrahedron Lett. 2013, 54, 3079) that an aromatic carboxylic acid 14 could be oxidatively decarboxylated to the chloride 15. Gérard Cahiez of the Université Paris 13 found (Adv. Synth. Catal. 2013, 355, 790) mild Cu-catalyzed conditions for the reductive decarboxylation of aromatic carboxylic acids, and Debabrata Maiti of the Indian Institute of Technology, Mumbai found (Chem. Commun. 2013, 49, 252) Pd-mediated conditions for the dehydroxymethylation of benzyl alcohols (neither illustrated). Pravin R. Likhar of the Indian Institute of Chemical Technology prepared (Adv. Synth. Catal. 2013, 355, 751) a Cu catalyst that effected Castro-Stephens coupling of 16 with 17 at room temperature. Arturo Orellana of York University (Chem. Commun. 2013, 49, 5420) and Patrick J. Walsh of the University of Pennsylvania (Org. Lett. 2013, 15, 2298) showed that a cyclopropanol 20 can couple with an aryl halide 19 to give 21.


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