Photoadditions of 2-morpholinopropenenitrile to naphthalene carboxylic acids

2-Morpholinoporpenenitrile (2) is added with high regioselectivity to elect ronically excited 1-naphthoic acid (4a) with formation of a [2+2]-cycloaddu ct 5a bearing an exo-oriented morpholino ring as well as a [4+2]-cycloadduc t 6a with an endo-oriented morpholino ring only. Esterification with diazom ethane allows for the isolation of products 5b and 6b, and at the same time hydrolysis products 7 and 8 are built up. For methyl naphthalene-1-carboxy late (4b) an analogous product pattern was observed. Under otherwise the sa me irradiation conditions 2-naphthoic acid does not react with 2. In a [2+2 ]-photocycloaddition naphthalene-1,4-dicarboxylic acid (9a) and 2 give rise to the [2+2]-exo-product 10 only. Surprisingly, a product has been observe d in very low yield, which is probably a follow-up product from a Paterno-B uchi-reaction of 2 to one of the carboxylic acid groups. The excited single t and triplet state properties of the three naphthalene carboxylic acids ar e described, the triplet quantum yields are substantial and the triplet ene rgies at 234-248 kJ mol(-1). Both states are readily quenched by 2, the rat e constants are greater than or equal to 1 x 10(10) M-1 s(-1) and less than or equal to 2 x 10(9) M-1 s(-1) for the excited singlet and triplet state, respectively.