Synthesis of the possible carcinogenic dihydrodiol and diol epoxide of phthalazine

cis-3,5-Cyclohexadiene-1,2-diol derivatives: facial selectivity in their Diels–Alder reactions with ethylenic, acetylenic and azo dienophiles

The Diels-Alder reactions of maleimide with the acetonide derivative (6a) of cis-3,5-cyclohexadiene-1,2-diol (1a) in various solvents showed facial selectivities ranging from 1 : 1 to 1 : 9. The same derivative 6a reacted in benzene with ethylenic dienophiles with generally modest facial selectivity, but acetylenic dienophiles added exclusively anti to the oxygen functions of 6a. Dimerization of cyclic acetals 6a and 7 was mainly, but for 6a not exclusively, by anti addition with respect to both the diene and the dienophile partners. Reactions of azo dienophiles with derivatives of 1a were predominantly by anti addition, but the diol itself (1a) gave the syn adduct as the major product.