The reaction of olefins with chloromethoxymethane (CMM) and excess formic acid in ether, in the presence of ZnCl2 or HgCl2, afforded mainly four products, 1-chloro- and 1-formyloxy-2-(formyloxymethyl)alkanes, and 3,5-dialkyl-4-chloro- and 3,5-dialkyl-4-(formyloxy)tetrahydropyrans, in various yields. In the case of styrene, the chief products were limited to the former two. Similar products were obtained