Studies In Synthetic Photochemistry

Part A. The photocycloaddition of alkenes or allene to steroidal enones has been shown to occur in the adsorbed state. This reaction normally occurring from the (less hindered) (alpha) side has been found to be directed towards the (more hindered) (beta) side by adsorption of the steroidal enone on a dry silica gel and alumina surface. The adsorption of the enone on silica gel also, apparently, disfavours the conformational inversion in the intermediate, 1,4 biradical, required for the formation of trans-fused products. The changes in composition of the products are frequently such as to be synthetically useful, and in some cases, e.g. the addition of allene to epi-testosterone (15c) and testosterone propionate (15a) on alumina, lead to complete reversal of stereochemistry to that observed in the methanolic solution. ('13)Cmr and x-ray diffraction analysis have been used to establish the structure of a 1,3 allene photocycloadduct with 3(beta)-acetoxy-(DELTA)('8,9)-cholesten-7-one; a mechanism of formation has been proposed involving a triplet carbene. For a series of cyclic enone-allene photocycloaddition it is shown that normally favored formation of the (beta)(gamma)-regioisomeric adduct in homogeneous systems can be shifted to favor the (gamma)(delta) adduct on a silica gel surface. The formation of (gamma)(delta) adduct is explained by assuming that the initial bond formation occurs at C(,(alpha)) of enone.;Part B. A photochemical approach to Illudinine involving "de Mayo" reaction namely, photocycloaddition of enolized heterocyclic 1,2-dione (23) to 3,3-dimethyl cyclopentene has been proposed. A strategy for the synthesis of 5,6-dihydro-2-pyridin-7-one (25) involving regioselective metalation of pyridine, intramolecular acylation of enamine and homolytic acylation of pyridine has been attempted. The synthesis of (gamma)-homocinchomeronic acid dimethyl ester (38), a precursor to the enone (23) involving regiospecific nucleophilic addition to 3-pyridyl-(DELTA)('2)-oxazoline has been carried out; a mechanism of formation, involving a lactam, has been proposed. Alternatively (38) is synthesized involving Arndt-Eistert rearrangement of (beta)-diazoacetyl nicotinate (50).