Diastereoselective Three-Step Route to o-(6-Nitrocyclohex-3-en-1-yl)phenol and Tetrahydro-6H-benzo[c]chromen-6-ol Derivatives from Salicylaldehydes

This work was aimed at preparing o-(6'-nitrocyclohex-3'-en1'-yl)phenol and tetrahydro-6H-benzo[c]chromen-6-ol derivatives in three steps starting from salicylaldehydes. Initially 3-acetylcoumarins were prepared in the absence of solvent using a solid base catalyst such as PS-TBD. In the second step, the Diels-Alder reactions of 3-nitrocoumarins and 3-acetylcoumarins under thermal conditions or in the presence of hafnium chloride yielded the corresponding tetrahydrobenzo[c]chromenones. The final part of the work was dedicated to the transformation of nitro-tetrahydrobenzo[c]chromenones into o-(6'-nitrocyclohex-3'-en-1'-yl)phenol derivatives in aqueous medium and to the conversion of acetyl tetrahydrobenzo[c]chromenones into the corresponding tetrahydro-6H-benzo[c]chromen-6-ol derivatives in tetrahydrofuran (THF), in the presence of tetrabutylammonium fluoride (TBAF) on silica. In every case the diastereoselectivity was complete and the reaction yields were high.