%0 Journal Article
%A Overman, Larry E.
%A Wolfe, John P.
%D 2002
%T New Cationic Olefin Cyclization−Pinacol Reactions.
Ring-Expanding Cyclopentane Annulations That Directly Install
Useful Functionality in the Cyclopentane Ring
%U https://acs.figshare.com/articles/journal_contribution/New_Cationic_Olefin_Cyclization_Pinacol_Reactions_Ring-Expanding_Cyclopentane_Annulations_That_Directly_Install_Useful_Functionality_in_the_Cyclopentane_Ring/3695445
%R 10.1021/jo025927r.s003
%2 https://acs.figshare.com/ndownloader/files/5785824
%K cycloalkanone
%K iminium salts 64
%K KHCO
%K ci
%K cyclic transition states
%K Cyclopentane
%K carbon side chain
%K triflic anhydride
%K cyclopentane C 2 position
%K diastereoselectivitie
%K DTBMP
%X Two new tandem cationic olefin cyclization−pinacol reactions that provide cyclopentane-fused
cycloalkanone products are described. Treatment of cis-1-[2-alkenyl-2-(triethylsiloxy)cycloalkyl]but-3-en-2-ol derivatives 21−24 with triflic anhydride at −78 °C affords cycloalkanones 31−34 in
54−90% yields with diastereoselectivities of typically >20:1. In this unusual transformation, the
starting cycloalkanone is ring-expanded and fused to a 2-alkenylcyclopentane fragment. Reaction
of cis-(2-siloxy-2-alkenylcycloalkyl)pyrrolidin-1-ylethanones 15−17 with triflic anhydride and 2,6-di-tert-butyl-4-methylpyridine (DTBMP) at −20 to +65 °C followed by hydrolysis of the intermediate
iminium salts 64 with aqueous KHCO3 affords cycloalkanediones 46−48 in moderate yield and
high diastereoselectivity (>20:1). These are the first examples of ring-expanding cyclopentane
annulations that directly introduce a carbon side chain or carbonyl functionality at the cyclopentane
C2 position. The high diastereoselectivities observed in these reactions are believed to arise from
reaction through highly organized cyclic transition states.
%I ACS Publications