Question

Explain the differences in the observed reaction outcome of the following reactions: A. Unequally substituted epoxides, like 1,1-dimethyloxirane, produce two different regiochemical products under acidic and basic conditions. Briefly justify/rationalize each result. O: NaOMe HO .Me HOMe O: H2S04 Me. OH HOMe B. Rationalize the stereochemical outcome of the following reaction Me Me Me Me mCPBA, DCM (00

Answer 1

Na OMe Me this reaction proceeding through the familiar SN2 mechanism followed by a transfer of proton. nucleophile (HO-) attacks the epoxide at the least substituted position (C2) and results in inversion of stereochemistry H2SO4 MeO OH 田 ○H OMe weaker nucleophiles react with epoxides the epoxide must first be protonated so the reaction conditions are acidic. Protonation makes the epoxide more electrophilic and creates a stable carbocation oMe, Me mCPBA epoxide forms at less croweded side, two methyl groups gives steric hinderence at above side of the compound, due to this epoxidation takes place at below side