Isoflavylium Salts

Isoflavans and Isoflavylium Salts.—Cycloaddition of dimethylsulphoxonium methylide (183) to cyclohexanediones (or their enols) (182) gave good yields of 3,4,5,6,7,8-hexahydro-3-hydroxy-2//-l-benzopyran-5-ones (184). When the O-acetate (185) of this was pyrolysed at 150 °C, a 2 1 mixture of 2H- (186) and 4//-benzopyrans (187) was obtained.  

Isoflavylium perchlorates (188) are converted (in high yields) into 2-aryl-benzofurans when treated with Pr OH, HCl, and H2O2. The mechanism shown 

Pellicciari, M. Curini, P. Ceccherelli, and B. Natalini, Gazz. Chim. Itai, 1978,108, 671. 

A new type of natural isoflavan has been isolated from the roots of Abrus precatorius. Chemical and spectral evidence supports structure (189).Among several isoflavans present in Lotus hispidus is a new compound, 5,4, -dimethoxy 7,2 -dihydroxyisoflavan (5-methoxyvestitol).  

---

The reaction of the dimethyl acetal of phenylacetaldehyde with salicylaldehydes enables 3-phenylbenzopyrylium salts to be prepared (82JHC97) and the reaction of arylmalondial-dehydes with phloroglucinol provides another variation on this theme which also affords isoflavylium salts (81AJC2647). 

---