Novel reaction products from simple organic reactions: Delineation of reaction pathways
In continuation of our interest in the synthesis of biologically active, natu- ral and synthetic compounds, we have come across some surprises even with simple reac- tions like alkylation, condensation and rearrangement, which have resulted in the forma- tion of some unusual novel products. Structures of these were assigned on the basis of their detailed spectral analysis and also confirmed in a few cases by X-ray crystal studies. Mechanistic aspects of the plausible routes of their formation have also been presented. NOVEL PRODUCTS OF FRIES REARRANGEMENT The Fries rearrangement is an exceedingly convenient and general method for the preparation of hydroxyketones from phenol esters and the formation of product(s) depends upon the reaction conditions used (ref. 1). It finds wide application in synthetic organic chemistry since both the acid and the phenol from which the phenol esters are derived can be varied. Metal promoted (ref. 2), anionic (ref. 3) and Photo Fries rearrangements (ref. 4), because of their specific advantages are gaining more importance these days for the regiospecific prepara- tion of varieties of new compounds. Beside these, Fries reaction has been also used for the preparation of various synthons, required for the synthesis of number of polycyclic compounds like benzofurans, steroids, coumarins and isocoumarins. We, in continuation of our interest in the field of natural product synthesis, envisaged the preparation of synthon 1, required for the synthesis of Candirone (5-hydroxy-2-(4-hydroxyphenyl)-3,6,8-trimethoxy-4H-1- benzopyran-Cone) (Z), isolated by Parmar et a1 (ref. 5), from the seeds of Tephrosiu cundidu. Interest in the synthesis of 2 was due to the rare oxygenation pattern (structure revised recently; ref. 6) and also because it was isolated from the extract that has been earlier found to possess strong insecticidal activity (ref. 7)Sarin et a1 (ref. 8) have also observed the activity against human epidermoid carcinoma of the nasopharynx in tissue culture (9KJ3) in 50% ethanolic extract of the plant. s$ #yHR*