The synthesis of naphthosultine and benzodisultines and their pyrolysis with dienophiles: Studies on o-naphthoquinodimethane and bis-o-quinodimethane

Abstract

Sealed tube reactions of the naphthosultine 8 with a series of electron-deficient dienophiles (fumaronitrile, N-phenylmaleimide, dimethyl fumarate, and dimethyl acetylenedicarboxylate) in toluene at 180 degreesC gave corresponding 1:1 cycloadducts 11-14 in various amounts along with rearranged naphthosulfolene 7 in 67-95% yields. The reaction of 1,2,4,5-tetra(bromomethyl)benzene with Rongalite (sodium formaldehyde sulfoxylate) and tetrabutylammonium bromide in DMF gave benzodisultines 17 and 18 in a combined yield of 56%. Sealed tube reactions of benzodisultines 17 and 18 with a series of dienophiles in xylene at 200 degreesC gave corresponding 1:1 and 1:2 cycloadducts 20-27. The results suggested that thermal extrusion of sulfur dioxide from these sultines led to either o-naphthoquinodimethane 6 (from 8) or bis-o-quinodimethane 19 (from 17 and 18); subsequent trapping of these reactive intermediates by dienophiles and SO2 gave various 1:1 and 1:2 Diels-Alder adducts in modest to excellent yields.