Asymmetric Synthesis of 3,4-Dihydrocoumarins by Rhodium-Catalyzed Reaction of 3-(2-Hydroxyphenyl)cyclobutanones

3,4-Dihydrocoumarin derivatives were synthesized in a highly enantioselective manner from 3-(2-hydroxyphenyl)cyclobutanones through enantioselective carbon−carbon bond cleavage. A cascade reaction with electron-deficient alkenes introduced a carbon−carbon bond at the 5-position of the dihydrocoumarins.