Methods of synthesis of cyclobutenediones

Issue in Honor of Prof. S. Swaminathan ARKIVOC 2005 (xi) 48-77 NH2O NH2O NH2 O Decomposition N NH t-Butyl hypochlorite NH N 25 oC O OO 83 82 70% Scheme 50 It has been reported that the vapour phase pyrolysis of indanetrione 84,79a and 38579b bezyloxyphthalide give traces of benzocyclobutenedione 78, whereas phthalamidodiphenylsulphoxide 86 gives benzocyclobutenedione in 35-70% yield under similar conditions (Scheme 51).79c 84 O O O 600 oC/ 0.02 mm -CO 78 O O -N2 and R2SO 420 oC/ 0.01 mm R = Me 35% 86 N O O N S O R R 33% R = Ph 70% PhCOO H 560 oC/ 0.1 mm O O -PhCOOH O O 85 Scheme 51 Synthesis of benzocyclobutenediones, on multi-gram scale, was achieved by flash vacuum pyrolysis of the Diels-Alder adducts of phthalazine-1,4-diones 87 with anthracene, cyclopentadiene80 or indene80 (Scheme 52). Among these, the anthracene adduct 88a gave better yields.81 O O O N N O O O O N N O O 500oC NH2NH2 Pb(OAc)4 87 Anthra- cene - Eq. 44 78 88a N N O O 71-98% 64-88% 500oCCyclopenta diene 88b Scheme 52 ISSN 1424-6376 Page 72 ©ARKAT USA, Inc 0