SUBSTITUENT EFFECTS ON PHOSPHONATION OF γ-CHLOROPROPYL ARYL KETONES WITH TRIETHYL PHOSPHITE

• Published in: Phosphorus, sulfur, and silicon and the related elements Vol. 131; no. 1; pp. 129 - 139
• Main Authors: Yu, Jen-Wen, Shih, Chung-Chieh, Huang, Steve K.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.12.1997
• Subjects: Carbonyl group-assisted mechanism; Oxycyclopentyl phosphonate; Substituent effect: Rate constant; γ-Ketophosphonate
• ISSN: 1042-6507; 1563-5325
• DOI: 10.1080/10426509708031601

Phosphonation of γ-chloropropyl aryl ketones 1 with triethyl phosphite yielded oxycyclopentyl phosphonates 2 and γ-ketophosphonates 3. Formation of 2 was greatly facilitated by the presence of electron-releasing p-substituents on the phenyl group, particularly the methoxy group, which may delocalize the electrons of the methoxy oxygen towards carbonyl oxygen through resonance effect. The linear Hammett plots for 2 showed negative p value of −2.33 (r = 0.993) for the solution with TEP/1 ratio of 4.5 and −3.09 (r = 0.999) for TEP/1 ratio of 1.5. In contrast, the formation of 3 occurred through a carbonyl group-assisted reaction pathway and the Hammett plot with a positive ρ value of 1.33 (r = 0.986) indicated that the reaction was accelerated by the presence of deactivating halogen as substituents, through the inductive effect. The direct replacement of halogen via S N 2 mechanism displayed an expected rate constant of 0.67 × 10 −6 Lmol −1 s −1 , and the formation of 3 (Y = H) was observed to occur at the rate of 3.83 × 10 −6 Lmol −1 s −1 . This result indicates that an S N 2 mechanism was not important for the formation of γ-ketophosphonates.