ON THE USE OF 1,3-DIENYLBORONATES IN DIELS-ALDER REACTIONS .1. A STRATEGY TOWARDS THE SYNTHESIS OF CLERODIN

A construction of the pivotal C-9-C-11 junction between the two subuni ts of clerodin 1 is proposed via a stereocontrolled tandem Diels-Alder /allylboration process. 1,3-Dienylboronate 8 was formed by hydroborati on of enyne 7 and underwent Diels-Alder cycloaddition with methyl acry late. The resulting allylboronate was then directly condensed with 4-( benzyloxy)butanal 12 yielding cyclohexene 14a (63% from catecholborane ), which displayed the desired C-9-C-11 stereochemistry. The protected alcohol 19a was then converted via a smooth oxidative decarboxylation process into cyclohexenone 21, which is a key intermediate in the tot al synthesis of clerodin.