Zum Ablauf der Wittig-Reaktion : zyklische oder ringoffene Zwischenstufen ?
Low temp. 31P NMR indicated that the reaction of Ph3P+C-RR1 (I, R = R1 = H, Me) with R2COR3 (R2 = R3 = H; R2 = Ph, R3 = H) under salt free conditions gave the corresponding oxaphosphetane (II); in the presence of Li salts, esp. in Et2O, Ph3P+CRR1CR2R3OLi X- (III) were formed. II (R = Li, R1 = Me, R2 = H, R3 = Ph), formed from II (R = R2 = H, R1 = Me, R3 = Ph) and alkyllithium reagents, rearranged slowly at -78 Deg and rapidly at -20 Deg to give Ph3P+C-MeCH(OLi)Ph. The reaction of I with benzaldehydes had r 1.1 which indicated that the transition states were highly polar and that the ylide acted as a nucleophile. The intermediacy of III in the Wittig reaction and in the formation of the oxaphosphetane was discussed. [on SciFinder (R)]
Keywords: Reaction constant (for Wittig reaction of benzaldehyde); Wittig reaction (intermediates in); Nuclear magnetic resonance (of phosphorus-31 ; in Wittig reaction intermediates); Kinetics of Wittig reaction (of triphenylphosphonium ylides with benzaldehyde ; Wittig reaction intermediate betaine; oxaphosphetane intermediate Wittig reaction
Physical Organic Chemistry
Inst. Chim. Org.,Univ. Lausanne,Lausanne,Switz.
written in German.
7723-14-0 Role: PRP (Properties) (NMR of, in Wittig reaction intermediates); 100-52-7 Role: RCT (Reactant), RACT (Reactant or reagent) (Wittig, kinetics of); 57043-22-8 Role: RCT (Reactant), RACT (Reactant or reagent) (phosphorus-31 NMR and ring opening of); 57043-19-3; 57043-20-6; 57043-21-7; 57043-23-9; 57043-24-0 Role: PROC (Process) (phosphorus-31 NMR of); 1754-88-7; 3487-44-3; 19493-09-5; 19493-10-8 Role: RCT (Reactant), RACT (Reactant or reagent) (reaction of, with benzaldehydes, kinetics of); 104-87-0; 104-88-1; 105-07-7; 123-11-5; 455-19-6; 587-04-2 Role: RCT (Reactant), RACT (Reactant or reagent) (reaction of, with ylides, kinetics of); 50-00-0 Role: RCT (Reactant), RACT (Reactant or reagent) (with triphenylphosphonium methylide, intermediates in)
Record created on 2006-03-03, modified on 2016-08-08