Reaction with aluminium selenide

Ley reported that selenium promoted carbocyclization reactions can also be effected by the enolic olefinic bonds of -dicarbonyl compounds [111]. These reactions occur with N-PSP in the presence of zinc iodide, tin tetrachloride or aluminium trichloride. An example is reported in Scheme 33. In the intermediate 219, derived from the -ketoester 218, cyclization through the oxygen atom to afford 220 is kinetically favoured. This reaction, however, is reversible, and upon prolonged reaction times and in the presence of strong acids the carbocyclization product 221 is formed. This procedure has been recently employed by Ley to effect the conversion of the alkenyl p-keto lactone 222 into the tricyclic selenide 223 (Scheme 33) which is a key intermediate in the preparation of model compounds with antifeedant activity [112]. 

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