Henry reaction guanidine-catalysed

Several enantiopure guanidines were studied as the catalysts for the Henry reaction of dibenzylamino aldehydes with nitromethane. (R)-l-(l-Naphthyl)ethylamine-derived guanidine catalysed the reactions of L-isoleucine-derived aldehydes with good diastereos-electivity [42]. 

Pahadi, N.K., Ube, H. and Terada, M. (2007) Aza-Henry reaction of ketimines catalysed by guanidine and phosphazene bases. Tetrahedron Letters, 48, 8700-8703. 

Ma, D., Pan, Q. and Han, R (2002) Diastereoselective Henry reactions of iV,iV-dihenzyl a-amino aldehydes with nitromethane catalysed hy enantiopure guanidines. Tetrahedron Letters, 43, 9401-9403. 

The domino Henry-Michael reaction of CH3NO2 with 7-oxo-hept-5-en-l-als RC0CH=CH(CH2)3CH=0, catalysed by the quinine-derived thiourea (288b) (<96% ee), followed by the tetramethyl guanidine (TMG)-catalysed retro-Henry-Henry reaction of the initially formed disubstituted cyclohexanols, led to a refinement of diastereoselectivity (to >99 1 dr) ... 

In 2013, Zhao et al. described a highly diastereo- and enantioselective synthesis of trisubstituted cyclohexanols based on a one-pot sequential tandem Henry-Michael reaction catalysed by a combination of a chiral cinchona alkaloid thiourea and 1,1,3,3-tetramethyl guanidine. This process occurred between nitromethane and 7-oxo-hept-5-en-l-als, providing the corresponding tandem chiral products as almost single diastereomers... 

Scheme 2.34 Tandem Henry-Michael-retro-Heniy reaction catalysed by a chiral cinchona alkaloid thiourea and 1,1,3,3-tetramethyl guanidine.

---