A STUDY ON THE Z-SELECTIVE HORNER-WADSWORTH-EMMONS (HWE) REACTION OF METHYL DIARYLPHOSPHONOACETATES

• Published in: Phosphorus, sulfur, and silicon and the related elements Vol. 133; no. 1; pp. 21 - 40
• Main Authors: Kokin, Keisuke, Iitake, Ken-Ichro, Takaguchi, Yutaka, Aoyama, Hiromu, Hayashi, Sadao, Motoyoshiya, Jiro
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 1998
• Subjects: AM1; Horner-Wadsworth-Emmons reaction; methyl (2,4-difluorophenyl)phosphonoacetate; methyl diarylphosphonoacetate; methyl Z-cinnamate; Z-selectivity
• ISSN: 1042-6507; 1563-5325
• DOI: 10.1080/10426509808032451

Experimental and theoretical studies were conducted to explore the Z-selectivities in the Homer-Wadsworth-Emmons (HWE) reaction employing several methyl diarylphosphonoacetates (3, 4, 5 and 6) and aldehydes. The Z-selectivity depended upon the reaction conditions such as the bases, reaction temperature, and the aromatic suhstituents on the phosphorus atoms but the almost phosphonoacetates used in the present study showed Z-selectivity in the reactions with both aromatic and aliphatic aldehydes. While the phosphonoacetate (3) with bis(2,4-difluorophenyl)phosphono group showed the highest Z-selectivity in all reaction conditions employed, decrease of the selectivity was observed in the case of some phosphonoacetates with diarylphosphono groups. These experimental results and the theoretical studies calculated by AM1 or 3-21G* ab initio methods suggested that the steric effect in the transition states of the addition steps was important rather than the electronic effect. A different aspect of the reaction courses between the Wittig and HWE reactions in the present computational chemistry was also described.