Reductive Radical Cyclisations of Bromo Acetals and (Bromomethyl)silyl Ethers of Terpenoid Alcohols

Article abstract of DOI:10.1002/hlca.19910740117

The tin hydride promoted and the reductive vitamin B12 catalysed radical cyclisation of mixed 2-bromoacetaldehyde acetals and of (2-bromomethyl)dimethylsilyl ethers of allylic terpenoid alcohols has been investigated: 3-oxadeca-5,9-dien-1-yl radicals undergo 5-'exo' cyclisation to oxolanes (Scheme 4), 3-oxa-2-siladeca-5,9-dien-1-yl radicals sequential 6-'endo' --> 5-'exo' tandem cyclisation to cis-3-oxa-4-silabicyclo<4.3.0>nonanes (Scheme 5), and 3-oxa-2-silatetradeca-5,9,13-trien-1-yl radicals sequential 6-'endo' --> 6-'endo' --> 5-'exo' triple cyclisation to trans-transoid-trans-12-oxa-11-silatricyclo<7.4.0.0^2.6>tridecanes (Scheme 6).