Methoxynaphthaldehydes as constituents of the heartwood of Diospyros quiloensis and their synthesis by the Stobbe condensation

Abstract

Seven compounds, five of them new, have been isolated from the heartwood of Diospyros quiloensis. The new compounds have been shown by chemical and spectroscopic methods, and by synthesis, to be 4,5,6,8-tetramethoxy-,5-hydroxy-4,6,8-trimethoxy-, 4,5,8-trimethoxy-, 4,5-dimethoxy-, and 5-hydroxy-4-methoxy-2-naphthaldehyde. The other two, 4,5,6-trimethoxy- and 6-hydroxy-4,5-dimethoxy-2-naphthaldehyde, have been isolated previously from a Diospyros species.

Related methoxynaphthoic acids and methoxynaphthaldehydes have been synthesised by Stobbe condensation and cyclisation. The structures of the compounds derived by cyclisation of the mono- and bis-condensation products of 3,4-dimethoxybenzaldehyde with ethyl succinate have been determined on the basis of spectral considerations and explained on stereochemical grounds.

The n.m.r. spectra of these substituted naphthoic acids and naphthaldehydes confirm the importance of the peri-effect and the large deshielding by an 8-methoxy-group on a proton in the 1-position.