Easily recyclable polymeric V(V) salen complex for the enantioselective O-acetyl cyanation of aldehydes

Enantioselective cyanoformylation of aldehydes catalyzed with solid base mediated chiral V(V) salen complexes

“…1). 19,59,60 Earlier, we 58 and others 46,48,49 have reported that the presence of a cocatalyst greatly influence the chiral metal complexes catalyzed enantioselective addition of ethylcyanoformate to aldehydes. The cocatalysts used so far for this reaction are essentially organic bases and are nonrecoverable after the catalytic run is over.…”

“…The enhanced reactivity in the case of polymeric complex as against monomeric complex may be attributed to the increase reactive sites which may be working in co-operation. 59,60,63 In all the catalytic runs, the (R)-form of V(V) salen complexes 1 and 2 as catalysts resulted in to (S) enantiomer of the product ethyl cyanohydrincarbonates.…”

“…The complex 1 was synthesized by the reported procedure. 59,60 The solution of poly[(R,R)-N,N 0 -bis-{3-(1,1-dimethylethyl)-5-methylene salicylidene} cyclohexane 1,2diamine] (0.799 g, 1.79 mmol) was dissolved in mixed solvent ethanol:CH 2 Cl 2 (3:2, 15 ml) to which an aqueous solution of vanadyl sulfate hydrate (0.453 g, 1.79 mmol in 2 ml water) was added drop-wise under an inert atmosphere at room temperature. The resulting solution was refluxed for 4 h and then cooled to room temperature with an extended stirring for 12 h while opening the side arm of the reaction flask for aerial oxidation.…”

“…58 Among all the catalytic systems reported for cyanoformylation of aldehydes hitherto none had reported the recyclablity of the essentially expensive catalyst which is desirable from economic point of view. In view of our on going interest in asymmetric cyanation reaction as well as making the catalyst recyclable, [59][60][61][62][63] we present here the use of V(V) polymeric and monomeric salen complexes 1 and 2 as efficient catalysts for the enantioselective cyanation of aldehydes using ethylcyanoformate as a source of cyanide in combination with hydrotalcite as cocatalyst. Excellent yield (95%) and ee (94%) was achieved for the ethyl cyanocarbonate of 2-benzyloxybenzaldehyde with the added advantage of several times re-cyclablity of polymeric complex 1 with HT and alumina.…”

Using Soluble Polymer Supports To Facilitate Homogeneous Catalysis

“…95 Khan had earlier described chemistry similar to that in eq 59 using (CH 3 ) 3 SiCN to form O-trimethylsilyl cyanohydrins. That work used the same V(V) salen polymer 56 and afforded the S cyanohydrin TMS derivative from benzaldehyde in >94% conversion with an enantioselectivity of 96% ee for all four cycles.…”