Chloromethanesulfonylethene and Dichloromethanesulfonylethene: New Reagents for Tandem Diels−Alder/Ramberg−Bäcklund Reactions

Chloromethanesulfonylethene (3a) and dichloromethanesulfonylethene (3b) were prepared by oxidation of the adducts of ethylene and ClCH2SCl or Cl2CHSCl, respectively, followed by NaHCO3 dehydrochlorination. With dienes, 3a gave Diels−Alder adducts that, with base, underwent Ramberg−Bäcklund reaction, giving products corresponding to the adducts of the dienes and allene. Similarly, 3b gave Diels−Alder adducts that, with base in the presence of the novel chlorine source MeSO2CCl3, cleanly afforded products corresponding to the adducts of the dienes and 1,1-dichloropropa-1,2-diene.