Some unreported by-products from the reaction of 1,4-dien-3-one steroids with 2-(methylammo)benzethiol/BF3

In a previous report, it was demonstrated that the 3-carbonyl of androsta-1,4-dien-3,17-dione (ADD) can be selectively protected with 2-(methylamino)benzethiol in the presence of BF3 in good yield. We explored the applicability of this method for other 1,4-dien-3-one steroids and got the desired protective products in different yield. Other than the usual protected products, we also got some unexpected by-products, including benzathiazol[4,3-b]-estra steroids. Their structures were determined by spectral analysis.