C-C Bond Formation: The Chen/Yang Synthesis of Spirochensilide A
Patrick J. Walsh of the University of Pennsylvania and Jianyou Mao of Nanjing Tech University assembled the carboxylic acid 3 by the decarboxylative coupling of glutaric anhydride 2 with the bis-halide 1 (Nature Commun. 2020, 11, 5638. ). Franz Bracher of Ludwig-Maximilians University observed high equatorial selectivity in the conversion of 4 to 5 by sequential hydroboration and Suzuki-Miyaura cross-coupling (Eur. J. Org. Chem. 2020, 6270. ). Alakesh Bisai of the Indian Institute of Science Education and Research Bhopal prepared the ketone 8 by the Pd-mediated coupling of the enol carbonate 6 with the allylic alcohol 7 (Tetrahedron Lett. 2020, 61, 152129. ). Chao-Jun Li of McGill University devised a new method for carbon-carbon bond formation, the construction of 11 by the Ru-catalyzed coupling of the alcohol 9 with the hydrazone 10 (Nature Commun. 2020, 11, 6022. ).
Kaori Ando of Gifu University devised an effective protocol for ketone methylenation, demonstrating that Julia-Kocienski olefination with the sulfone 13 converted even the very challenging substrate 12 to the alkene 14 (J. Org. Chem. 2020, 85, 9936. ). Hiroaki Imoto and Kensuke Naka of the Kyoto Institute of Technology showed that the tetrahydroarsole 17 was an effective catalyst for the arsa-Wittig reaction, mediating the preparation of the unsaturated ester 18 by the coupling of the aldehyde 15 with the bromoester 16 (Chem. Eur. J. 2020, 26, 13400. ). Yunmi Lee of Kwangwoon University employed excess aldehyde 19 in the reductive coupling with the allene 20, leading via subsequent Oppenauer oxidation to the ketone 21 (Org. Lett. 2020, 22, 5806. ). In another application of Julia-Kocienski olefination, Professor Ando showed that addition of the sulfone 23 to the ketone 22 delivered predominantly the less-stable Z alkene 24 (Org. Lett. 2020, 22, 6907. ). Amir H. Hoveyda of Boston College assembled a detailed review of the role of ethylene in olefin metathesis (Angew. Chem. Int. Ed. 2020, 59, 22324. ).
Donald A. Watson of the University of Delaware devised conditions for the preparation of the nitro alkyne 27 by the alkylation of the nitroalkane 25 with the propargylic bromide 26 (Org. Lett. 2020, 22, 8106. ). Yikang Wu of the Shanghai Insitute of Organic Chemistry developed the diazophosphonate 29, a version of the Ohira-Bestmann reagent that does not require nucleophilic added alkoxide (Synlett 2009, 3037. ).
Hongchao Guo of China Agricultural University used a cinchona alkaloid-derived catalyst to mediate the coupling of 32 with the racemic allene 31, leading to the allene 33 in high ee (Angew. Chem. Int. Ed. 2020, 59, 19820. ). Qian Peng of Nankai University and Xiaoyu Yang of ShanghaiTech University found that a chiral phosphoric acid effectively directed the construction of the allene 36 by the addition of 35 to 34 (Nature Commun. 2020, 11, 5527. ).
Spirochensilide A (39), isolated from the great Shensi fir, Abies chensiensis, of central China, Tibet and northern India, significantly reduced physiological NO production. Jia-Hua Chen and Zhen Yang of Peking University established the key spiro center of 39 by the rearrangement of the epoxide 37 to the aldehyde 38 (J. Am. Chem. Soc. 2020, 142, 8116. ).