Trimethylsilylchloride-zinc chloride

Kametani and co-workers have demonstrated what may prove to be the most convenient and effective approach to the utilization of l-aza-1,3-butadienes for intramolecular [4 + 2] cycloadditions.37 Treatment of a,j3-unsaturated enamides with trimethylsilylchloride-zinc chloride provides in situ generation of 2-trimethylsilyloxy-l-aza-1,3-butadienes which are capable of effective intramolecular [4 + 2] cycloaddition (Table 9-II, entries 12-14). Selected conditions have permitted this in situ generation and subsequent intramolecular Diels-Alder cycloaddition of 2-trimethy-lsilyloxy-l-aza-1,3-butadienes to be conducted at 25°C,37b and these observations have found application in the total syntheses of ( )-epilupinine and ( )-tylophorine [Eqs. (14) and (15)].37c,b... 

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