A remarkable substituent effect on the enantioselectivity of tandem asymmetric epoxidation and enantiospecific ring expansion of cyclopropylidene alcohols: a new enantiocontrolled synthesis of (-)-debromoaplysin and (-)-aplysin

Abstract

A remarkable substituent effect by the tert-butyldimethylsiloxy group on the enantioselectivity of the tandem asymmetric epoxidation and enantiospecific ring expansion of 21) in high yield and high enantiomeric excess, was observed. This enabled us to accomplish a concise and highly enantioselective total synthesis of (-)-debromoaplysin ( 2) and (-)-aplysin (1), providing a new and general strategy for the enantioselective synthesis of biologically important substances having the dihydrobenzofuran

Semipinacol Rearrangement Induced by Cleavage of Dibromocyclopropane

“…In this transformation, a hydroxy group in a 1,2‐diol is activated with acids to generate a tertiary carbocation, which undergoes 1,2‐shift of a substituent at the α‐position of the remaining hydroxy group. Related methods involving the electrophilic activation of a C–C double bond in allyl alcohol A with electrophiles such as a halonium ion, proton, or metal ion, have been used to generate a tertiary carbocation adjacent to an alcohol moiety ( B ), which subsequently undergoes a 1,2‐shift to afford C (Scheme ).…”

An efficient synthesis of the precursor of AI-2, the signalling molecule for inter-species quorum sensing

“…Protection of the hydroxyl group of methyl glycolate with tert-butyldiphenylsilyl chloride (TBDPSCl), 14 followed by hydrolysis of the methyl ester with LiOH in THF/H 2 O afforded carboxylic acid 9 14 in 94% yield. Without purification 9 was converted into amide 10 14 using N,O-dimethylhydroxylamine hydrochloride and DCC in dichloromethane, in 85% yield.…”

Phytochemical and Biological Properties of Sesquiterpene Constituents From the Marine Red Seaweed Laurencia: A Review

“…Compound 117 displayed selective cytotoxicity to the HeLa cell line [79]. Another collection of L. tristicha (Shanwei, Guangdong Province, China) yielded the stereoisomers 4-bromolaur-11-en-1,10 β -diol (118) and 4-bromolaur-11-en-1,10 β -diol (119), along with the known laur-11-en-1,10 β -diol (120), but reported for the first time as a natural product [80,81].…”