CH2N2 at − 65° in THF yielded cycloadducts which eliminated N2 between − 40 and − 35° to give the corresponding phosphonodithioformate S-methanides ( =methylenesulfonium (dialkoxyoxidophosphino)(methylthio)methylides) 11 (Scheme 3). These reactive 1,3-dipoles were intercepted by aromatic thioketones to yield 1,3-dithiolanes. Whereas the reaction with thiobenzophenone (12b) led to the sterically more congested