A concise and enantioselective approach to cyclobutanones by tandem asymmetric epoxidation and enantiospecific ring expansion of cyclopropylidene alcohols. An enantiocontrolled synthesis of (+)- and (-)-.alpha.-cuparenones
A tandem Katsuki-Sharpless asymmetric epoxidation and enantiospecific ring expansion of 2-alkyl(or 2-aryl)-2-cyclopropylideneethanols (1a-i) afforded chiral 1-alkyl(or 1-aryl)-1-(hydroxymethyl)cyclobutanones (3a-i) in high yields and high enantiomeric excess. These compounds are potentially valuable synthons for the enantioselective creation of the quaternary carbons. Hence, this enabled us to accomplish a concise and enantioselective total synthesis of both (+)- and (-)-alpha-cuparenones (11).
Asymmetric construction of α,α–disubstituted cyclobutanones–enantioselective total synthesis of (–)-frontalin
Novel access to the chiral, α,α-disubstituted ketone 2-hydroxymethyl-2-methylcyclobutanone was developed, leading to an enantioselective total synthesis of (–)-frontalin, an aggregating pheromone of bark beetles.