Etude RMN(1)H et radiocristallographique de la stereochemie de 3-aryl-9b-hydroxy-1,3,3a,9b-tetrahydro-4H-thienobenzopyrane-1-carboxylates d'ethyle. Configuration et conformation

Article abstract of DOI:10.1016/0584-8539(93)80070-Q

The reaction of ethyl mercaptoacetate with some 3-arylidene-4-chromanones yields the corresponding ethyl 3-aryl-9b-hydroxy-1,3,3a,9b-tetrahydro-4H-thieno<3,4-c>benzopyrane-1-carboxylates.In spite of the presence of four chirality centers, the reaction is diastereospecific and gives a single diastereoisomer whose configuration and conformation were specified by its PMR data.The cis-fused tetrahydrothiophenic and dihydropyranic cycles lie in half-chair conformation.The 9b-hydroxyl and the 3-aryl groups are in a cis equatorial and pseudoequatorial disposition.The ester group, also cis with the hydroxyl group, presents a hydrogen bond with the hydroxyl.In the presence of an ortho-substituent at the phenyl group (particularly a chlorine atom), this phenyl group undergoes a notable rotation as is pointed out by a radiocristallographic study.A comparative study between the NMR and radiogcristallographic data allows the confirmation of the maintenance of the same conformation in solid and dissolved states.