1-Substituted allenylsilanes reacted with 3-alkoxycyclobutanones in the presence of
TiCl4 to afford 8-oxabicyclo[3.2.1]octan-3-ones stereoselectively. Nucleophilic attack
of allenylsilanes to a 1,4-zwitterionic intermediate formed from 3-alkoxycyclobutanones
and TiCl4 followed by 1,2-silyl migration, five-membered cyclization with an alkoxy group,
and seven-membered cyclization of titanium enolate was proposed. Deuteration and one-pot
Peterson olefination suggested that alkyl titanium species were formed after cyclization
to 8-oxabicyclo[3.2.1]octane skeletons.
Key words
cyclobutanone - allenylsilane - Lewis acid - 8-oxabicyclo[3.2.1]octane - alkyl titanium
bond