Copper-catalysed 1,6-addition of a benzyl Grignard reagent to a dienone: a new synthesis of ring C aromatic diterpenoids
Abstract
Copper(I) salts favour the 1,6-addition of m- and p-methoxybenzyl Grignard reagents to the dienone (2); acid-catalysed cyclisation of the products (3a, b) gives 2-oxopodocarpa-8,11,13-trienes while cyclisation of the allylic alcohol (5a) gives the A/B-cis isomer (6) in good yield.