REARRANGEMENT OF DERIVATIVES OF 1,3-DITHIAN-5-AMINE INTO BICYCLIC 2-THIAZOLIDINES. CRYSTAL STRUCTURES OF CIS- AND TRANS-1-(2-ARYL-1,3-DITHIAN-5-YL)-2-THIOUREAS AND CIS- AND TRANS-5-ARYL-3-IMINO-7,7A-DIHYDRO-1H,3H,5H-THIAZOLO(3,4-C)THI