Metal-Mediated C-C Ring Construction: The Lawrence Synthesis of Illicinone A
Alois Fürstner of the Max-Planck-Institut für Kohlenforschung devised a Rh-Bi paddlewheel complex that mediated the enantioselective addition of the diazo ester 1 to the alkyne 2, leading to the cyclopropene 3 in high ee (J. Am. Chem. Soc. 2021, 143, 5666. ). Marcos G. Suero of ICIQ showed that with the proper choice of Rh carboxylate, the cyclopropane 5 could be made the dominant product from the cyclization of the diazo ester 4 (Angew. Chem. Int. Ed. 2021, 60, 6177. ).
Hui Lv of Wuhan University constructed the lactone 7 via the cyclocarbonylation of the prochiral cyclopentenol 6, followed by oxidation (Nature Commun. 2021, 12, 5279. ). Zhenfeng Zhang and Wanbin Zhang of Shanghai Jiao Tong University used a Rh catalyst to effect the alkene migration and subsequent cyclization that converted the unsaturated aldehyde 8 to the cyclopentanone 9 (Angew. Chem. Int. Ed. 2021, 60, 8997. ). Man-Bo Li of Anhui University and Jan-E. Bäckvall of Stockholm University assembled the cyclopentenol 12 by combining the allene 10 with the alkyne 11 (Angew. Chem. Int. Ed. 2021, 60, 670. ). Barry M. Trost of Stanford University developed the [3 + 2] cycloaddition of the sulfone 14 to the nitroalkene 13 to prepare the exomethylene cyclopentane 15 (Org. Lett. 2021, 23, 2460. ).
Pengcheng Qian of Wenzhou University and Liming Zhang of the University of California, Santa Barbara cyclized the alkynyl aldehyde 16 to the cyclohexanol 17. Cyclopentanols could also be formed in high ee (Nature Catal. 2021, 4, 164. ). Yu-Hua Deng, Fangzhi Peng and Zhihui Shao of Yunnan University achieved high ee in the preparation of 20 by the allylation of the vinylogous ester 18 with 19 (Org. Lett. 2021, 23, 920. ).
Xiufang Xu and Weiwei Zi of Nankai University constructed the cycloheptanone 23 by combining the cyclic carbonate 21 with the diene 22 (J. Am. Chem. Soc. 2021, 143, 3595. ). Wusheng Guo of Xi'an Jiaotong University described a parallel investigation (Org. Lett. 2021, 23, 351. ). Geoffroy Sorin of the Université de Paris showed that the allylic alcohol of the enyne 24 directed the steric course of the low-valent Ti cyclization to the cycloheptanol 25 (Chem. Commun. 2021, 57, 3603. ).
Zhen-Jiang Xu of the Shanghai Institute of Organic Chemistry and Chi-Ming Che of the University of Hong Kong devised an iron catalyst that directed the absolute sense of the Diels-Alder addition of the enone 27 to the diene 26, leading to the tetracyclic cyclopentanone 28 (Org. Chem. Front. 2021, 8, 1910. ). En route to thebainone A, Guangbin Dong of the University of Chicago rearranged the prochiral cyclobutanone 29 to the tetracyclic ketone 30 (Angew. Chem. Int. Ed. 2021, 60, 13057. ).
One enantiomer of illicinone A (32) was isolated from the leaves of the Taiwan tree Illicium arborescens. The other enantiomer was isolated from the leaves of the shrub Illicium tashiroi. Andrew L. Lawrence of the University of Edinburgh used three equivalents of a Binol-derived aluminum complex to effect the enantioselective rearrangement of 31 to 32 (Org. Lett. 2021, 23, 3248. ).