Synthesis of diazaheterocycles with a bridgehead nitrogen by photocyclisation of N-substituted alicyclic imides

Abstract

N-(Dialkylaminomethyl)-succinimides or -glutarimides give 1,3-diazabicyclo [3.3.0] octanes or -[4.3.0]-nonanes on irradiation in acetonitrile, accompanied by variable amounts of the parent imide. Two diastereoisomers of the products can be obtained, and the relative stereochemistry assigned on the basis of n.m.r. data. With unsymmetrical substrates mixtures of products are formed that demonstrate orientational preferences. Analogous N-substituted pyrrolidin-2-ones do not give photocyclised products (an unusual cleavage product is isolated in low yield), and similar dihydrouracils are relatively photostable. N-(Dialkylaminoethyl) aliphatic imides give azepine- or azocine-diones on irradiation, whereas N-(dialkylaminopropyl) compounds undergo photocyclisation to products with a new perhydro-1,4-diazepine ring (as do a corresponding 3,4,5,6-tetrahydrophthalimide and phthalimide, although photoreduction is a major process for the latter system). An N-(dialkylaminobutyl) succinimide does not give products with a new perhydrodiazocine ring. An N-(dialkylaminoethyl) maleimide and the analogous 3,4,5,6-tetrahydrophthalimide give compounds that contain a new piperazine ring, which is in contrast to the saturated imide analogues but similar to the corresponding phthalimide; this process competes effectively with the more usual photoreactions of maleimides involving the carbon–carbon double bond.