[2 + 3]‐Cycloadditions of Phosphonodithioformate S‐ Methanides with CS, NN, and CC Dipolarophiles

The reaction of the methyl (dialkoxyphosphinyl)‐dithioformates (= methyl dialkoxyphosphinecarbodithioate 1‐oxides) 10 with CH 2 N 2 at − 65° in THF yielded cycloadducts which eliminated N 2 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 isomers 15 regioselectively, a mixture of both regioisomers was obtained with 9 H ‐fluorene‐9‐thione ( 12a ). Trapping of 11 with phosphono‐ and sulfonodithioformates led exclusively to the sterically less hindered 1,3‐dithiolanes 16 and 18 , respectively ( Scheme 4 ). In addition, reactive CC dipolarophiles such as ethenetetracarbonitrile, maleic anhydride, and N ‐phenylmaleimide as well as the NN dipolarophile dimethyl diazenedicarboxylate were shown to be efficient interceptors of 11 ( Scheme 5 ).