Indolizidone

Anthraquinone photosensitised irradiation of tertiary N-allylamines in the presence of aP-unsaturated esters gives good yields of lactams. Using pyrex-filtered output (X>290 nm) from a 450 W medium pressure Hanovia lamp, for example, A-allylpiperidine and methyl methacrylate reacted in acetonitrile to give a 2 3 diastereomeric mixture (2S, 9S 2R, 95) of the indolizidone 1. 

The scope and limitations of the alkylation of racemic and achiral 2-lithiopiperidines, obtained by transmetallation of the corresponding stannes, is reported <95JOC(60)5763>. Anthraquinone photocatalyzed addition of piperidines to a,P-unsaturated esters led to a novel route to indolizidone (56) (Scheme 42) <95JCS(P1)1797>. 

Most, a,jS-unsaturated esters other than methyl methacrylate undergo facile Michael type addition with primary and secondary amines to yield A -addition products. By carrying out the anthraquinone photosensitized addition of several secondary amines with a, -unsaturated esters at low temperatures ( 0°C), the thermal reactions could be controlled without adversely affecting the photochemical free radical reactions. Using this procedure, indolizidone, pyrrolizidone and a mixture of heliotridone and pseudoheliotridone was synthesized (Scheme 72) [326]. 

A range of cyclic diazo ketoamides have been studied by Padwa and co-workers to generate seven-membered carbonyl ylides [172]. The Rh(II)-catalyzed reaction of the amido diazo ketoester 229 was found to cleanly afford the rearranged indolizidone 232 via the intermediates 230 and 231 (Scheme 72). 

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