Selected chemo - ecological studies of marine opisthobranchs from indian coasts.

A new synthesis of 2 , 2 - dimethyl - 12 - [ 3 - methylbut - 2 - enyl ] - 2H , 6H - pyrano [ 3 , 2 - b ] xanthen - 6 - one (7) is described from 1 , 3 - dihydroxyxanthone and involved the preparation of a linear dihydropyranoxanthone (26) , its conversion into the pyranoxanthone (14) and its prenylated derivative (31) followed by a Claisen rearragement leading to the target substrate (7).