Nitroallyl addition

The mechanism of this cyclization involves a conjugate addition of the enamine (100) to the nitroallyl ester (101) to give 102, which on elimination produced 103. The immonium salt 103 undergoes proton transfer to give enamino nitro olefin 104, which cyclizes to an enamine (107) via 105 and 106. Hydrolysis of 107 produces the ketone (108). Depending on the reaction conditions and the structure of the enamine and nitroolefin components employed, intermediates can be isolated (equation 19). 

SMP enamines have a very broad range of applications as d synthons. Cyclohexanone SMP enamine can be used for efficient Michael additions to nitroalkenes, Knoevenagel acceptors, and to a nitroallylic ester in a [3 + 3] carbocyclization with excellent stereoselectivities (eq 1). The synthesis of y-oxo-a-amino acids using SMP enamines has been developed (eq 2). ... 

A different approximation was reported by Tang, Li, and co-workers [56] by using Seebach s nitroallylic acetate reagent 85, cyclohexanones, and proline-thiourea derivative XXVI as a catalyst. Nitroallylic acetate reacts with cyclohexanones via a double Michael addition, affording the final fused bicyclic ketones 86 in excellent yields and stereoselectivities (Scheme 10.24). 

In addition, Seebach has extended his work on nitroallyl pivalates as multicoupling reagents (Vol. 6, p. 208) and has now published the synthesis and reactions of the nitroallyl pivalates (22) and (23) and the chloride (24) (Scheme 35). These new reagents furnish adducts with a variety of nucleophilic species and, as with previously reported analogues, the acceptor properties of the nitro-group may be further exploited. 

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