Tetrahedron Le~tas. Vol.31. No.37. pp 52935296. 1990 Priitcd in GreatBritain oo4o-4039190 $3.00 + .oo Pcrgamm Rcss plc INTRAMOLECULAR PHOTOCHEMICAL REACTIONS OF N-ALKYL-5-PHENYL+PENTEN-l-AMINES Frederick D. Lewis* and G. Dasharatha Reddy Department of Chemistry, Northwestern University, Evanston, IL 60206 USA Summary: trradiation of N-alkyt-S-phenyl-4-penten- 1 -amines results in the formation of intramolecular styrene-amine ad&c& and disprqwttiti4nation products. Increasing the buk of the N-atkyl group increases the regibsetectivity of N-H transfer fawdng the formation of piperidine vs. pyrrolidne prvducts and favors disproportionation vs. cy&ation. Intramolecular photochemical alkene-amine additions are attracting increasing attention as a method for the preparation of nitrogen heterocyclesl. We recently reported that the irradiation of o- styrylaminoalkanes results in efficient intramolecular addition. 2 For example, irradiation of cis- or trans-N-methyl-5-phenyl-4-penten-l-amine (la) results in the formation of a ca. 2/l ratio of regioisomeric adducts 2a and 3a with isolated yields of > 60% (eq 1). Variation in the length of the polymethylene chain connecting the styryl and amino groups from 1 to 5 permitted the photochemical synthesis of cyclic amines of ring size ranging from 4 to 6. In addition, 1H NMR analysis of the adduct 2a obtained using the N-deuterated amine trans-la-N-d established that N- D addition to styrene is a stereospecific syn process. In order to further explore the potential utility of intramolecular styrene-amine addition for the stereocontrolled synthesis of cyclic amines, we have investigated the effect of increasing the bulk of the N-alkyl group. In view of our proposed mechanism (eq l), increased bulk might be expected to affect (a) the rate constant for intramolecular electron transfer quenching, (b) behavior of the resulting biradical intermediates. the regioselectivity of N-H transfer, and (c) the t’h-N’ AH, 2a (1) The trans-N-alkyl-5-phenyl-4-penten-l -amines la-c were prepared via the reaction of trans- 5phenyl-4-pentenoic acid with the appropriate primary amine, followed by reduction of the resulting amide with LiAIH4. The singlet lifetimes of la-c as determined by single photon counting are all significantly shorter (< 0.5 ns) than that of trans-1 -phenylpropene (11.6 ns).s Thus increasing the 5293