Attempts to cyclize the adduct (11)

Although the adduct (11) was heated in wet o-xylene for 24 h under reflux after treatment with aq. sodium hydogen carbonate solution, the cyclized product, 3-methoxy-2-trifluoromethyl-1H-pyrido[2,1-b]benzothiazol-1-one (13), was not formed contrary to our expectation. 4,4,4-Trifluoro-2-pentafluoroethyl-1-(2-pyridyl)-3-trifluoromethylbut-1-ene and the corresponding 1-(2-benzothiazolyl) derivative were quantitatively converted to 5a and 3-pentafluoroethyl-2-trifluoromethyl-1H-pyrido[2,1-b]benzothiazol-1-one.¹ The reaction at higher temperature than the bp of o-xylene gave many products.