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

• Published in: European journal of organic chemistry Vol. 2015; no. 27; pp. 6033 - 6039
• Main Authors: Wahl, Benoit, Lee, Darren S., Woodward, Simon
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-09-2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Conjugate addition; Fumaric esters; Michael addition; Rearrangement; Trichloromethylation
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201500730

The 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.
Mild and efficient conditions for the Michael addition of TMSCCl3 to symmetrical and unsymmetrical fumarates is reported. Using a catalytic initiator in the form of X– (X = OAc, Cl, F), the 1,4‐addition products undergo a kinetic elimination to yield dichloroalkenes and under thermal rearrangement to form dichloropent‐2‐enedioates.