New methods for reductive free-radical cyclizations of α-bromoacetals to 2-alkoxytetrahydrofurans with activated chromium(II)-acetate
作者:Claus Hackmann、Hans J. Schäfer
DOI:10.1016/s0040-4020(01)81285-0
日期:1993.5
free-radical cyclization of α-bromoacetals 4 to 2-alkoxytetrahydrofurans 5 in 54–93% yield induced by activated chromium(II)-acetate. Four new methods have been developed in order to activate the transition metal. Two of them require only catalytic amounts of chromium(II)-acetate, because it can be regenerated in situ chemically or electrochemically. The diastereoselectivity of the cyclization depends on