Guanidine bases in synthesis: Extending the scope of the corey-chaykovsky epoxidation

Guanidine bases, such as 1,5,7-triazabicyclo[4.4.0]dec-1-ene (TBD) or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-1-ene (MTBD), are highly effective reagents for the in situ generation of sulfonium ylides from sulfonium salts in Corey-Chaykovsky epoxidation reactions of aldehydes. These reactions proceed rapidly to produce the corresponding epoxides in excellent yields and with high selectivity for the trans product. Significantly, this reagent combination is applicable to both nonenolizable and enolizable aldehydes and α,β-unsaturated aldehydes.