Anomalous Z-isomer content in Wittig reaction products from keto-stabilised ylides with ortho-heteroatom substituted benzaldehydes

Abstract

Publication informationTetrahedron Letters, 53 (49): 6701-6704Publisher Elsevier Item record/more information

The modern interpretation of the Wittig reaction mechanism

“…Some triphenylphosphine-derived stabilised ylides do not undergo Wittig reactions or require heating to effect the reaction, 3 but we have observed methyldiphenylphosphinedrived stabilised ylides to react rapidly with aldehydes even at -78 °C. 38,39 This is consistent with the observation of Frøyen that 80 the reaction rates of fluorenylides with p-nitrobenzaldehyde increases with successive replacement of the P-phenyl groups of the ylide phosphonium moiety with P-ethyl groups. 53 A very significant aspect of the Wittig reaction is that, broadly speaking, the nature of the ylide used in a Wittig reaction dictates 85 the stereoselectivity of the reaction.…”

E,Z-Selectivity in the reductive cross-coupling of two benzaldehydes to stilbenes under substrate control

“…Following the study on electronic effects, and inspired by the Z-directing ortho-effect described by Gilheany and coworkers, 29,31 a series of experiments with different ortho-substituted benzaldehydes were performed ( Table 2).…”

“…This so-called "ortho-effect" 27,28 can be exploited to synthesize enriched Z-stilbenes, as shown by Gilheany and co-workers. [29][30][31] As shown in Scheme 1a, the reaction gives rise to higher proportions of Z-alkene when the aldehyde has an ortho-substituent. In contrast, an ortho-substituent on the phosphonium salt has no such effect, and the thermodynamically more stable E-stilbene is formed (Scheme 1b).…”

“…From a mechanistic viewpoint, the Z-directing effect of the ortho-substituent arises from a secondary bonding interaction between the phosphorus and the ortho-heteroatom during the transition state. 29,31 In recent years, we have been interested in developing new phosphorus mediated cross-coupling reactions of carbonyl compounds to olefins. [32][33][34][35] In one of our latest work, we have been able to couple two different benzaldehydes selectively to unsymmetrical 1,2-disubstituted stilbenes via phosphaalkene (2) and phosphinate (3) intermediates (Scheme 2).…”

Insight into Triphenylamine Donor Thiazole Acceptor Conjugated Oligomer to Analyze Emission Behavior towards Aggregation Pathway

“…The lowest number average molecular weight ( M n ) of TPA‐TZ has been found as 1615 Da with PDI of 1.02, for TPA‐BTZ has been found as 1396 Da with PDI of 1.00 and for TPA‐BTDZ has been found as 2147 Da with PDI of 1.02. The reason has Wittig formed product results low molecular weight of oligomers …”