Cis selectivity of salt-free Wittig reactions: a "Leeward Approach" of the aldehyde at the origin?
In THF at 25 Deg, Et3P:CHMe reacts with heptanal, Me3CCHO, PhCHO and p-ClC6H4CHO to afford, after 2-4 h, the corresponding olefins in 89-99% yield. In each case the trans isomer prevails, cis/trans ratios ranging from 33:67 to 4:96. The remarkable cis-stereoselectivity of Wittig reactions using triphenylphosphonium alkylides is now attributed to a very specific and almost rigid orientation of the Ph groups around the P atom, which sterically hinders approach to the aldehyde in a way that would lead to the formation of a trans-substituted oxaphosphetane. [on SciFinder (R)]
Keywords: Stereochemistry (cis selectivity of Wittig reactions of triethylethylidenephosphorane); Aldehydes Role: RCT (Reactant) ; RACT (Reactant or reagent) (cis selectivity of Wittig reactions of ; with triethylethylidenephosphorane); Wittig reaction (cis selecti ; cis selectivity Wittig reaction; stereochem Wittig reaction; ylide phosphorus Wittig reaction stereochem
CAN 97:163132 29-7 Organometallic and Organometalloidal Compounds Inst. Chim. Org.,Univ. Lausanne,Lausanne,Switz. Journal 0002-7863 written in English. 1754-88-7 Role: RCT (Reactant), RACT (Reactant or reagent) (Wittig reaction of, with aldehydes); 17847-85-7 Role: RCT (Reactant), RACT (Reactant or reagent) (Wittig reaction of, with aldehydes, stereoselectivity of); 100-52-7; 104-88-1; 111-71-7; 630-19-3 Role: RCT (Reactant), RACT (Reactant or reagent) (Wittig reaction of, with triphenyl- and triethylphosphonium ethylides); 690-08-4P; 762-63-0P; 766-90-5P; 873-66-5P; 1879-52-3P; 1879-53-4P; 6434-77-1P; 6434-78-2P Role: SPN (Synthetic preparation), PREP (Preparation) (prepn. of)
Record created on 2006-03-03, modified on 2016-08-08