CYCLOADDITION REACTIONS OF 1,3-BENZOTHIAZINES. 3. RING TRANSFORMATIONS OF 1,3-BENZOTHIAZINE DERIVATIVES. II. CONVERSION OF 6α-ARYL-7α-CHLORO-2,3-(2′,3′-DIALKOXYBENZO)-1-THIAOCTEMS INTO 2-CARBOMETHOXY-3-ARYL-7,8-DIALKOXY-4,5-DIHYDRO-1,