Unusual reaction of a substituted benzothiazoline with sulphuryl chloride: Formation of a 2,2′-(ethane-1,2-diylidene)bis-1,4-benzothiazine dye

3-Acetyl-2-ethyl-2-phenylbenzothiazoline (1) reacts at room temperature with SO2Cl2 to give, in 67% yield, the dye (2), by way of the 1,4-benzothiazine (3) arising by a new ring expansion reaction

Trimeric aldolization product of 1,4-benzothiazine

2H-1,4-Benzothiazine, the parent system of the mammalian phaeomelanic pigments, is a highly unstable molecule which readily undergoes a reversible aldolization to form, mainly, the cyclic trimer (5)

A New Synthesis of 4H-1,4-Thiazines and Benzothiazines

Benzothiazines I [R1 = H, R2 = Me, Ph; R1 = Me, R2 = Ph; R1R2 = (CH2)4] and thiazines II [R1 = H, R2 = Me; R1R2 = (CH2)4] were prepd. in 23-59% yield by treatment of III or IV with p-MeC6H4SO3H in MePh at reflux for 30 min.  III were prepd. in 13-81% yield by oxidn. of the resp. sulfide; unsym. 2-substituted dihydrobenzothiazoles gave a mixt. of 2 diastereoisomeric sulfoxides