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

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:ci s-6 were from 1.1:1 to 1.8:1 and the mechanism of the formation 6 is propos ed to proceed through the formation of nitrile oxides 5 to undergo intramol ecular nitrile oxide-olefin cycloaddition (INOC). Nitronates 16, prepared f rom 1 with allyl alcohol and base, can be converted into methoxycarbonyl ni tronates 22 by treating the solution with methyl chloroformate and catalyti c amount of 4-dimethylaminopyridine (DMAP) in the presence of different amo unts of triethylamine. Intermediates 2 2 can either undergo intramolecular alkoxycarbonyl nitronate-olefin cycloaddition (IAOC) to generate highly ste reoselective product trans-14 or undergo INOC to yield trans-14 and cis-14. The application of this improved methodology to synthesize different heter ocyclic products 10, 26, and 27 is reported. (C) 1999 Elsevier Science Ltd. All rights reserved.