Studies on intramolecular alkylation. IX. The synthesis of tricyclic dienones suitable for the synthesis of 13-hydroxygibberellins

Abstract

2-Hydroxy-6-methoxy-1,2,3,4-tetrahydro-2-naphthoic acid and its 8- methoxy isomer were converted into trichloroacetate and dichloroacetate derivatives and thence to diazoketones (2), (3), (12) and (13). The acid-catalysed cyclization of these substrates to the dienones (6), (7), (16) and (17), respectively, was then studied. The trichloroacetoxy derivatives gave the best yields of dienones.

Norcaradienes from the Intramolecular Cyclopropanation Reactions of Diazomethyl Ketones. Valuable Intermediates for the Synthesis of Polycyclic Diterpenes

“…13 Insertion could be expected to become a more dominant pathway when such electronic factors coincide with the formation of a 5-membered ring, 14 as in the case of the 7-methoxy isomer (entry 4). The impact of benzylic activation is also apparent with the formation of cyclobutanones from the 8-methoxy 15 and 6,8-dimethoxy 16 derivatives. The formation of significant amounts of alkenes 9 from these substrates, however, indicates that with sufficient activation, C-C bond forma-tion may not necessarily be concerted with hydride transfer, especially where cyclobutanone formation would be involved.…”