An unexpected synthesis of novel oxygen-bridged 1,5-benzothiazepine derivatives and their reductive five-membered-ring opening

A convenient procedure is reported for the preparation of benzofuro-annelat ed 2-phenyl-1,5-benzothiazepine derivatives by oxidative cyclocondensation of phenolic beta-diketones with o-aminothiophenol in DMSO. The regiochemist ry of these compounds is proven by HMBC signals and the existence of a five -bond F-19,C-13-2 coupling. Surprisingly, treatment with LiAlH4 at room tem perature led to a double reduction under opening of the five-membered ring. Refluxing such solutions with a higher amount of LiAlH4 gave rise to a fur ther reduced derivative possessing the trans-configuration. All structures (regio- and stereochemistry) were assigned an the basis of NMR spectroscopi c data.