Influence of Ag(I) and Li(I) Catalysts for 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides. Reversal of the Stereochemistry

X=Y–ZH compounds as potential 1,3-dipoles. Part 64: Synthesis of highly substituted conformationally restricted and spiro nitropyrrolidines via Ag(I) catalysed azomethine ylide cycloadditions

“…The cycloaddition of the less hindered imines 6a,d with anthracene nitrostyrene 7a afforded single cycloadducts endo-9a,b in good yield (72-80%)( Table 1, entries 1 and 2), whereas imines 6b,c from alanine and phenylalanine failed to react under the same conditions due to the steric hindrance between the Me and Bn groups of the imines and the anthracenyl group of the dipolarophile. 10 have observed similar results in the 1,3-dipolar cycloaddition of glycine imine with different nitroolefins and they have reported that silver salts favour the formation of exo-cycloadduct in the case of nitroolefins with bicyclic aryl groups. They have suggested that secondary orbital interactions of the aryl groups play a major role in this change of stereoselectivity.…”

“…This type of compound e.g 3-5 is accessible via 1,3-dipolar cycloaddition of appropriate azomethine ylides and nitrostyrenes. Nyerges et al 8 applied this cycloaddition methodology to the stereoselective synthesis of azacephalotaxine 8a,b and indolic aza-analogues 8c of cephalotaxine. They have also reported a new method for the synthesis of substituted pyrroles 8d from nitropyrrolidines.…”

“…They have also reported a new method for the synthesis of substituted pyrroles 8d from nitropyrrolidines. Several authors explored the 1,3-dipolar cycloaddition of both non-stablized 9 and stablized 10 azomethine ylides with nitroolefins for the synthesis of substituted nitropyrrolidines. For stabilized azomethine ylides it was concluded that lithio-azomethine ylides 10 undergo preferential formation of endo-cycloadducts whilst silver salts favour the formation of exo-cycloadducts.…”

“…Several authors explored the 1,3-dipolar cycloaddition of both non-stablized 9 and stablized 10 azomethine ylides with nitroolefins for the synthesis of substituted nitropyrrolidines. For stabilized azomethine ylides it was concluded that lithio-azomethine ylides 10 undergo preferential formation of endo-cycloadducts whilst silver salts favour the formation of exo-cycloadducts. Further work showed that incorporating certain groups in the aromatic moiety of aryl azomethine ylides modifies the stereoselectivity 10b .…”

The Effect of Phase-Transfer Catalysis in the 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides − Synthesis of Substituted Prolines Using AgOAc and Inorganic Base in Substoichiometric Amounts

“…[12,21] The cycloaddition reaction under PTC conditions was very sensitive to steric hindrance. For example, trans-cinnamaldehyde or methyl crotonate did not give the desired products.…”