An Efficient Synthesis of Some Substituted Vinylic Chloroformates: Reaction Scope and Limitations

Article abstract of DOI:10.1021/jo00311a015

2,2-Dichlorovinyl chloroformate is isolated in 50percent distilled yield when chloral is treated with phosgene and zinc dust in 2:1 methyl acetate/ether.The reaction has been extended to other α-chloro and α-bromo aldehydes and ketones in which both other α-positions are occupied by either halo and/or alkyl groups.The reaction fails with hydrogen in an α-position.Examples include the synthesis of Cl2C=C(Me)OC(=O)Cl in 23percent yield, MeC(Cl)=CHOC(=O)Cl (56percent, E:Z=1:1.1), Cl2C=C(C6H5)OC(=O)Cl (66percent), and 2-methyl-1-cyclohexenyl chloroformate (68percent).Similar treatment of α-halo esters gives only the C-acylated products expected from a Reformatsky type reaction, while ketenes are the well known products from α-halo acid chlorides.However, acyl cyanides and acyl phosphonates, with leaving groups intermediate between fluoride and alkoxide, are converted to chloroformates; e.g., Me2C=C(CN)OC(=O)Cl in 67percent yield and Me2C=COC(=O)Cl in 83percent yield.Carbonates and urethans from these chloroformates are of interest as monomers, pesticides, and chemical intermediates.