We found that boron trifluoride etherate was a better catalyst for the formation of the thiazine G than sulfuric acid; the former gave a 75% yield of G, and, in addition, dibenzyl sulfide and K-benzylbenzamide were isolated and identified from the boron fluoride reaction. With sulfuric acid as catalyst, the yield of thiazine was 5570 starting with the tertiary alcohol, but only 15% starting with the unsaturated compound F; the latter yielded much material ...
