Tremorgenic Indole Alkaloids. 9. Asymmetric construction of an Advanced F-G-H-ring Lactone precursor for the Synthesis of Penitrem D
作者:Amos B. Smith、Ernest G. Nolen、Ryuichi Shirai、Frances R. Blase、Mitsuaki Ohta、Noritaka Chida、Richard A. Hartz、Duke M. Fitch、William M. Clark、Paul A. Sprengeler
DOI:10.1021/jo00129a025
日期:1995.12
Lactone (+)-12 is envisioned as the precursor to the F-G-H rings of penitrem D (4) in our ongoing synthetic venture. The efficient, stereocontrolled introduction of the vicinal quaternary methyl groups present the major challenge in the construction of this subunit. Our first route to (+/-)-12 was marked by low overall yield (<2%) and the instability of several key intermediates; these deficiencies were rectified in a second-generation approach that produced optically active material (18 steps from 19a, 2.1% overall). The successful strategies exploited enolate generation via either conjugate additions to alpha,beta-enones or the Evans oxy-Cope rearrangement as key regiochemical control elements.