Studies on Rutaceae-part III. Reactions and Rearrangements of Prenyl and Prenyloxy Coumarins

Department of Pure Chemistry, University College of Science, Calcutta-700 009 During our study on the reactions and rearrangements of prenyl and prenyloxy coumarins interesting reactions and rearrangements were observed. 7-Methoxy-8- (1',2'-epoxy-3'-methylbut-3'-enyl)coumarin (phebalosin) (II) on oxidation with osmium tetroxide afforded 7-methoxy-coumarin-8-yl-acetaldehyde (XXXII) while 7-methoxy­8-(2'-hydroxy-3'-methylbut 3'-enyl) coumarin (auraptenol) (III) with m-chloroperbenzoic acid underwent rearrangement to 7-methoxy-8-(3'-formyl-but-2'-enyl) coumarin (XXX). The epoxy-lactone system of 7-methoxy-coumarin-6-(3', 4cepoxy-3'-methyl)--y­butyrolactone (micromelumin) (IV) opened up with boron tribromide to give 7-methoxy­coumarin-6-(3'-bromo-3'-methyl-4'-hydroxy)-7-butyrolactone (XXXIII) while with 10% oxalic acid ring opening was accompanied by further degradation to give 6-formy1-7- methoxy coumarin (angelical) (XXXIV). Chromous chloride reduction of micro­melumin (IV) afforded deoxymicromelumin (XXXVI) and oxidation with chromic acid/ sulphuric acid degraded it to umhelliferone-methyl-ether-6-carboxylic acid (XXXVII) Dehydrogenation of dihydroseselin (VII) with DDQ resulted in an unusual product, 3,6- thchloro-dihydroseselin (XXIV)