1,2-Asymmetric Induction in the Intramolecular [2+2] Cycloadditions of Keteniminium Salts. Enantioselective Syntheses of (−)-Dihydroactinidiolide and (−)-Anastrephin
作者:Osamu Irie、Kozo Shishido
DOI:10.1246/cl.1995.53
日期:1995.1
1,2-Asymmetric induction in the intramolecular [2+2] cycloadditions of the keteniminium salts resulted in the preferential formation of optically pure bicyclo[4.2.0]octan-7-ones (13a,b). These cycloadducts, 13a and 13b, were successfully converted into the key intermediates of (−)-dihydroactinidiolide and (−)-anastrephin, respectively.
C-substituted α,β-unsaturated ester 5 having a terminal aldehyde functionality, was effectively achieved using SmI2 in THF-HMPA. Starting with the major cyclization product 6, enantiospecific total synthesis of (−)-anastrephin. 1 was completed.
Total syntheses of (-)-anastrephin, (-)-epianastrephin, and their 7a-epimers: use of samarium(II) iodide-mediated intramolecular reductive coupling for the construction of their hexahydrobenzofuran-2(3H)-one skeletons
D-Glucose-derived alpha,beta-unsaturated ester 17, which includes a geminally and differntially substituted gamma-carbon and a terminal aldehyde functionality, was subjected to a SMI2-Mediated intramolecular reductive coupling reaction in a THF solution containing 1/10 volume of HMPA. The reaction proceeded with moderate stereoselectivity to provide a diastereomeric mixture of hexahydrobenzofuran-2 (3H)-ones, in which cis-fused product 25 was obtained as the major isomer in 35% isolated yield. Two trans-fused coupling products 26 (17%) and 27 (14%) were also obtained. Starting from major product 25, the insect sex attractants (-)-anastrephin (1) and (-)-epianastrephin (2) were synthesized enantiospecifically. Two unnatural stereocongeners, (-)-7a-epi-anastrephin (3) and (-)-7a-epi-epianastrephin (4), were also derived from 25.