1,4‐Addition of TMSCCl3 to (E)‐Fumaric Esters and Thermal Rearrangement of the Adducts to 3,4‐Dichloropent‐2‐enedioates

Abstract

AbstractThe diesters (E)‐RO2CCH=CHCO2R [R = Et, CH2Ph, iPr, iBu, tBu, 2‐ethylhexyl, (–)‐menthyl, (–)‐bornyl] undergo 1,4‐trichloromethylation with Me3SiCCl3 in 84–95 % yield with Bu4NX (X = OAc, Cl, F; 0.5–10 mol‐%) as an initiator. Optimal catalysis is attained with X = OAc and F; chloride is less effective, bromide is inadequate. Poor regioselectivity but high yields are demonstrated by mixed diesters (2 examples, both > 80 %). Heating of the trichloromethyl adducts, in the presence of Bu4N(OAc), leads to equilibrating, approximately equimolar, mixtures of RO2CC(=CCl2)CHCO2R and RO2CCH=CClCHClCO2R above 100 °C (7 examples). The latter component is produced under thermodynamic control, which can be isolated pure in some cases. The former is the kinetic product of E2 elimination.