Iminium carbonic acid derivative salts. XI . Synthesis of N,S ‐containing heterobicycles from N ‐protected 2‐methylthio‐1,3‐thiazinium and 2‐methylthiothiazoüum salts. Part 3. Reaction of N ‐protected 2‐methylthio‐1,3‐thiazinium and 2‐methylthiothiazolium salts with 3‐amino‐2‐cyano‐3‐arylacrylonitriles

N ‐Boc‐protected 2‐memylthio‐1,3‐thiazinium 1 and 2‐methylthiothiazolium iodides 2, 3 obtained from the corresponding 3,4,5,6‐tetrahydro‐2 H ‐1,3‐thiazine‐2‐thiones and thiazolidine‐2‐thiones by the action of methyl iodide were reacted with 3‐armno‐2‐cyano‐3‐arylacrylonitriles forming the cyclic isothioureas 5–7 . The protection group was removed with trifluoroacetic acid whereupon the desired cyclisation to 3,4‐dihydro‐2 H ,6 H ‐pyrimido[2,1‐ b ][1,3]thiazines 8a‐c, 8a′‐c′ and thiazolo[3,2‐ b ]pyrimidines 9a,b, 9a′,b′, 10a,b took place.