Microwave-assisted one-pot synthesis of 2-aryl-5,6-dihydro-4H-1,3-thiazines via reaction between Lawesson’s reagent and allyl arylamides derived from Morita–Baylis–Hillman acetates

A one-pot synthesis of 2-aryl-5,6-dihydro-4H-1,3-thiazines from the allyl arylamides afforded from the Morita–Baylis–Hillman acetates of acrylates has been developed. The protocol comprises of Lawesson’s reagent-mediated transformation of allyl arylamide to thioamide followed by tandem intramolecular sulfa-Michael reaction under microwave condition to afford the products as a mixture of syn and anti isomers. Based on a plausible mechanism syn and anti-isomers are proposed as the kinetic and thermodynamic products, respectively. Further it has been experimentally demonstrated that the syn isomer is transformed to the anti isomer via prolonged heating.