NAPHTHOQUINONES . ON OXIDATIVE CYCLIZATION OF ISOLAPACHOL TO DEHYDRO-ALPHA-LAPACHONE AND PROTOTYPAL STUDIES RELATED TO SYNTHESIS OF LAPACHOL AND ITS DERIVATIVES

The reaction of isolapachol (2) with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) gives a mixture of dehydrα-lapachone and dehydro-β-lapachone (e.g., 3 and 4). Treatment of the mixture with dilute acid-ethanol causes an “ortho-para” rearrangement of the latter compound (e.g., 4), and 3 is then isolated in an over-all 60% yield. Birch reduction (in the absence of ethanol) of 3 gives an acidic fraction (66%) comprised of a 7:3 mixture of isolapachol (2) and lapachol (1). In the presence of ethanol, Birch reduction gives an acidic fraction (33%) comprised of lapachol (1) and hydrolapachol (5) in the ratio 3:2, respectively. © 1969, American Chemical Society. All rights reserved.