PhCH=P[MeNCH(2)CH(2)](3)N: a novel ylide for quantitative E selectivity in the Wittig reaction

Area of Science:

• Organic Chemistry
• Stereoselective Synthesis
• Organophosphorus Chemistry

Background:

• The Wittig reaction is a cornerstone for synthesizing alkenes from carbonyl compounds.
• Controlling stereochemistry, particularly achieving exclusive E-alkene formation, remains a significant challenge in Wittig reactions.

Purpose of the Study:

• To investigate the stereochemical outcome of the Wittig reaction using a novel semi-stabilized phosphorus ylide, P[MeNCH(2)CH(2)](3)N.
• To elucidate the factors governing the observed high E-selectivity and its robustness.

Main Methods:

• Synthesis of the semi-stabilized ylide P[MeNCH(2)CH(2)](3)N from a commercially available nonionic base.
• Reaction of the ylide with various aldehydes to form alkenes.
• Analysis of reaction products for yield and stereoselectivity (E/Z ratio).
• Determination of the X-ray molecular structure of the ylide.

Main Results:

• The ylide P[MeNCH(2)CH(2)](3)N reacted with aldehydes to produce alkenes in high yields.
• Quantitative E-selectivity was consistently observed, irrespective of the metal ion, temperature, or solvent polarity.
• X-ray crystallography provided structural insights into the ylide.

Conclusions:

• The novel ylide P[MeNCH(2)CH(2)](3)N is a highly effective reagent for stereoselective E-alkene synthesis via the Wittig reaction.
• The observed robust E-selectivity can be rationalized using the Vedejs model of Wittig reaction stereochemistry.
• This ylide offers a reliable method for accessing E-alkenes with predictable stereochemical outcomes.