An Enantioselective Approach toward 3,4-Dihydroisocoumarin through the Bromocyclization of Styrene-type Carboxylic Acids

A facile and enantioselective approach toward 3,4-dihydroisocoumarin
was developed. The method involved an amino-thiocarbamate catalyzed
enantioselective bromocyclization of styrene-type carboxylic acids,
yielding 3-bromo-3,4-dihydroisocoumarins with good yields and ee's.
3-Bromo-3,4-dihydroisocoumarins are versatile building blocks for
various dihydroisocoumarin derivatives in which the Br
group can readily be modified to achieve biologically important 4-O-type
and 4-N-type 3,4-dihydroisocoumarin systems. In addition, studies
indicated that, by refining some parameters, the synthetically useful
5-exo phthalide products could be achieved with good yields and ee's.