The synthesis of 1‐tosylalkyl isocyanates and N(1‐tosylalkyl)carbamoyl chlorides from S‐ethyl N‐(1‐tosylalkyl) thiocarbamates

Abstract

Abstract1‐Tosylalkyl isocyanates, p‐CH3C6H4SO2CHRNCO (II), have been prepared in good yields from the reaction of S‐ethyl N‐(1‐tosylalkyl)thiocarbamates (I) and chlorine in a heterogeneous mixture of dichloromethane and aqueous sodium hydrogen carbonate. The reaction probably involves the intermediate formation of the previously unreported N‐(1‐tosylalkyl)carbamoyl chlorides, p‐CH3C6H4SO2CHRNR′COCl (IV), which may be isolated in high yield under anhydrous reaction conditions. In mildly alkaline solutions, these carbamoyl chlorides (R′  H) are smoothly converted into the 1‐tosylalkyl isocyanates. Ethanesulfonyl N‐methyl‐N‐(tosylmethyl)formamide (V), obtained by oxidation of S‐ethyl N‐methyl‐N‐(tosylmethyl)thiocarbamate, p‐CH3C6H4SO2CH2N(CH3)C(O)SC2H5, with hydrogen peroxide in acetic acid, was treated with chlorine to give tosyl chloride and ethanesulfonyl chloride. α‐Oxosulfones, p‐CH3C6H4SO2CH2N(CH3)C(O)SO2C2H5, are therefore unlikely intermediates in the formation of N‐(1‐tosylalkyl)carbamoyl chlorides.The reaction of S‐ethyl N‐(1‐tosylalkyl)thiocarbamates (I) with bromine in CH2Cl2/NaHCO3‐H2O in the presence of methanol gives methyl N‐(1‐tosylalkyl) carbamates, a result which can be best interpreted by assuming 1‐tosylalkyl isocyanates as intermediates.