Naturally occurring compounds related to phenalenone. Part V. Synthetic approaches to structures based on 8,9-dihydro-8,8,9-trimethylphenaleno[1,2-b]furan-7-one

Abstract

A number of possible synthetic routes to 8,9-dihydro-8,8,9-trimethylphenaleno[1,2-b]furan-7-one (21 b) and its 1,6-dimethoxy-(21a) and 1-hydroxy-6-methoxy-(21c) analogues have been explored. One successful method involved acid-catalysed cyclisation of the keto-lactone (22)[2-(2,7-dimethoxy-1-naphthoyl)-3,3-dimethylpentan-4-olide]; another utilised the Claisen rearrangement of the dimethylallyl ether (24b)[9-hydroxy-4-methoxy-3-(3-methylbut-2-enyloxy)phenalenone].