STUDIES IN THE CHEMISTRY OF CONJUGATED ACETYLENIC NITRILES

Abstract

Propynenitrile, is the parent compound in the series of conjugated acetylenic nitriles. The carbon-carbon triple bond which is activated by conjugation with the nitrile function offers immense scope for cycloadc tion and nucleophilic addition reactions. This thesis describes the preparation of substituted propynenitriles and their application in the synthesis of some heterocycies. The programme of work carried out has been presented as follows: CHAPTER I reviews briefly the importance of acetylenic compounds in organic synthesis and their occurrence in nature. The methods of preparation of conjugated acetylenic nitriles and their utility as synt ons for the preparation of different heterocyclic systems were discussed. An account of the history of discovery of Intramolecular Wittig reaction and its application for the synthesis of substituted propynenitrile was presented. The cycloaddition reactions of l-methyl-2(lH)-pyridinone with acetylenic dienophiles was reviewed. CHAPTER II describes the synthesis of oxo-substituted phos phorus ylides starting from triphenylphosphine, chloroacetonitrile and a carboxylic acid chloride. The oxo function is derived from phenoxyacetic acid or 2-methyl-2-phenoxy-propionic acid and derivatives containing a methyl or chloro or methoxy group in ortho or para position of phenyl ring. In the case of phenoxyacetyl chloride and its derivatives the transylidation method was used to prepare the oxo-ylides. In the 2-methyl-2-phenoxy-propionyl chloride the use o. external base replaces the transylidation step. CHAPTER III deals with the thermolysis of oxo-ylides and the occurrence of Tandem Intramolecular Wittig and Claisen rearrange ment reactions. Using this new reaction some benzofuran and 2H-chromene derivatives were svnthesised. The results provided evidence for the occurrence of 3,3-sigmatropic reaction and the intermediacy of allenyl substituted cyclohexadienones in the rearrangement of cyanopropargyl aryl ethers. Alternative mechanis tic pathways for the cyclisation of allenyl substituted cyclohexa dienones to benzofuran and 2H-chromene were discussed. CHAPTER IV describes the studies carried out on the cycloaddition reactions of some l-methyl-2(lH)-pyridinones with substituted propynenitriles. This study gave an insight into the aromatic character of the pyridone and also to the synthesis of novel N-substituted pyridones by the reaction of 2(lH)-pyridinone or its O-methyl derivative with substituted propynenitriles. All the new compounds synthesised in this work have been characterised using IR, H NMR and mass spectral data.