(i) NaBH4/LiCl-mediated reduction of 3-sulfonyl-2-benzylchromen-4-ones and 
NaBH4
(i) NaBH4/LiCl-mediated reduction of 3-sulfonyl-2-benzylchromen-4-ones and 
LiCl
(ii) sequential BF3·OEt2-mediated intramolecular annulation of the resulting 3-sulfonyl-2-benzylchroman-4-ols. 
BF3·OEt2