One-Pot Synthesis of Five-Membered Cyclic Thioethers or Ethers via Intramolecular Nitrile Oxide-Olefin Cycloaddition (INOC) or Intramolecular Alkoxycarbonyl Nitronate-Olefin Cycloaddition (IAOC) by the Use of Methyl Chloroformate

摘要

Reaction of #beta#-nitrostyrenes 1 with allyl mercaptan 2 in the presence of triethylamine generated unsaturated nitro sulfides 3 and then the solution was treated with methyl chloroformate (MCF) and was refluxed to obtain [3.3.0]bicyclic products trans-6 and cis-6 in one-pot. The ratios of trans-6 : cis-6 were from 1.1 : 1 to 1.8 : 1 and the mechanism of the formation 6 is proposed to proceed through the formation of nitrile oxides 5 to undergo intramolecular nitrile oxide-olefin cycloaddition (INOC). Nitronates 16, prepared from 1 with allyl alcohol and base, can be converted into methoxycarbonyl nitronates 22 by treating the solution with methyl chloroformate and catalytic amount of 4-dimethylaminopyridine (DMAP) in the presence of different amounts of triethylamine. Intermediates 22 can either undergo intramolecular alkoxycarbonyl nitronate-olefin cycloaddition (IAOC) to generate highly stereoselective product trans-14 or undergo INOC to yield trans-14 and cis-14. The application of this improved methodology to synthesize different heterocyclic products 10, 26, and 27 is reported.