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

Article abstract of DOI:10.1016/S0040-4020(99)00741-3

Reaction of β-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.