Palladium-Catalyzed Diastereo- and Enantioselective Wagner−Meerwein Shift: Control of Absolute Stereochemistry in the C−C Bond Migration Event
摘要:
Inducing absolute stereochemistry in Wagner-Meerwein shifts was examined in a ring expansion protocol. Initiated by generation of a pi-allylpalladium intermediate by hydropalladation of allenes, the ring expansion of allenylcyclobutanol substrates proceeded with excellent diastereo- and enantioselectivities. The results demonstrate that, during the C-C bond migration process, our chiral catalysts can control the stereochemistry of both the pi-allylpalladium intermediate and the corresponding migration bond. Moreover, the stereochemical outcome of the reaction can be rationalized very well with the working model of the chiral catalyst. The method provides an efficient way to synthesize highly substituted cyclopentanones with an alpha-chiral O-tertiary center which has various synthetic applications.
General approach to halogenated tetrahydrofuran natural products from red algae of the genus Laurencia. Total synthesis of (.+-.)-trans-kumausyne and demonstration of an asymmetric synthesis strategy
作者:Mark J. Brown、Timothy Harrison、Larry E. Overman
DOI:10.1021/ja00014a032
日期:1991.7
A general strategy for the synthesis of C 15 halogenated tetrahydrofuranoid lipids from red algae of the genus Laurencia has been developed. The central step is the convenient formation of hydrobenzofuranone (±)-5 on a large scale, and with complete stereocontrol, from the acid-catalyzed condensation of 1-vinylcyclopentanediol (3) and α-(benzyloxy) acetaldehyde (Scheme II). Starting with the chiral