Abstract
Intramolecular cyclization of ene-ynes catalyzed by platinum, ruthenium and gold complexes, Synthesis of polyarenes via electrocyclization are dealt in this thesis. The thesis consists of four chapters The first chapter explains Bergman cyclization of a variety of enediynes by catalytic platinum chloride (5 mol%) to give a cyclopentyl fused naphthalene rings in high yields. The presence of electron withdrawing and donating groups has a dramatic influence on the course of the reaction and it is very well demonstrated using different enediynes. The reaction mechanism has been proposed to involve the platinum π- alkyne intermediate. The second chapter deals with aromatization of enediynes via highly regioselective intramolecular nucleophilic additions on π- alkyne functionality using TpRuPPh3(CH3CN)2PF6 (10 mol%). This cyclization works for both inter and intramolecular modes, thus allowing an easy access to prepare functionalized aromatic compounds containing O, N heteroatoms. An addition/insertion mechanism is proposed based on the results of a series of experiments. The third chapter presents the oxidative cyclization of 2-ethenyl-1-(prop-2′-yn-1′-ol)benzenes to naphthyl aldehydes and ketones via catalytic oxidative cyclization using 5 mol% of AuClPEt3/H2O2. Gold-catalyst has found to be effective for the production of the desired ketones and aldehydes from diverse alcohol substrates. Terminal alkynes gave the aldehydes, and the internal alkynes gave the ketones in high yields. The final chapter discusses about the synthesis of spiro[4.5]trienones from 4′-methoxy -2-phenylethnyl-biphenyls by intramolecular Ipso- halocyclization induced by ICl and their acid mediated rearrangement. The key in ipso-halocyclization is the presence of the methoxy group at 4′ position. In presence of methoxy group at a position other than 4′, substrates failed to give the spiro compound, instead they gave iodophenanthrenes. An acid mediated mechanism was proposed for rearrangement. Iodophenanthrenes prepared were used as starting materials for other palladium assisted catalytic reactions like Heck coupling reaction.