Dehydrating agents enamine synthesis

The enamine reaction was introduced by Stork and his co-workers " and is widely used in organic synthesis. Enamines are a,(B-unsaturated amines and are obtained by the reaction of an aldehyde or ketone having a-hydrogen with a secondary amine in the presence of a dehydrating agent (such as catalytic amount of p-toluenesulfonic acid). 

TiCU is both a strong Lewis acid and a powerful dehydrating agent, and hence useful as a water scavenger in the synthesis of enamines. It is particularly useful for the preparation of enamines of acyclic ketones. It is recommended that TiCU is complexed with the amine before addition of the ketone. Highly sterically hindered enamines are available by this method (eq 51 ). Primary amines generally react very slowly with aromatic ketones to form imines. TiCU is a good catalyst (eq 52). ... 

A structurally unrelated agent is tazadolene (40). The synthesis of tazadolene begins with P-keto ester 37 and subsequent enamine formation with 3-amino-1-propanol followed by hydrogenolysis to give 38. This phenylhydroxymethyl compound is then dehydrated with hydrochloride acid to form olefin 39. Treatment with bromine and triphenylphosphine effects cycliza-tion to form the azetidine ring of tazadolene [10]. 

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