Chemistry of spironapthalelenones - synthesis and reactions of oxygen and nitrogen heterocycles

Abstract

The thesis entitled "CHEMISTRY OF SPIRONAPHTHALENONES – SYNTHESIS AND REACTIONS OF OXYGEN AND NITROGEN HETEROCYCLES" is presented in four chapters and an appendix. Chapter I is divided into two sections. Section I deals with the oxidation studies of spironaphthalenones (1) with DDQ. Reaction of spironaphthalenone (1) with DDQ in dry benzene resulted in two yellow compounds (A) and (B). The structures (2) and (3) respectively were assigned to these compounds on the basis of detailed spectral analysis and also by chemical transformations. ¹H–¹H COSY, ¹H–¹³C COSY, HMBC and NOESY studies of compound (3d) led to complete assignment of spectral data and solution conformation of the molecule. A novel macrocyclic lactone (5) has been isolated in the oxidation of dispironaphthalenone (4) with DDQ. Structure of this lactone has been confirmed by X-ray crystal structure analysis. Attempted synthesis of this as well as dihydrolactone by different routes are presented in Section II. Addition of different oxygen and carbon nucleophiles to dispironaphthalenone (4) resulting in the formation of bridged diketones (6) and (7) are discussed in Chapter II. A reinvestigation of the mechanism of formation of pyrrolotropone by the reaction of spironaphthalenone (8) with NH?OH·HCl is discussed in Chapter III. The generality of the reaction has been shown. Various 3-, 4-, 5'-substituted spironaphthalenones have been synthesized and their reaction with NH?OH·HCl has shown the involvement of a rearrangement in this reaction. All these results are presented in Section I. The reaction of various 1'-aryl-substituted spironaphthalenones (10) with NH?OH·HCl resulted in the formation of naphthopyrrole esters (12) instead of the dihydrotropone (11). Reaction of 3-, 4'-substituted spironaphthalenones gave isomeric esters showing involvement of a rearrangement. Oxime (12) was also isolated along with the ester (11) in the reaction of (10c) with NH?OH·HCl. Reaction of this oxime (12) with EtOH/HCl in presence of traces of acid gave the ester (12c), indicating that only one mole of NH?OH·HCl is required for the transformations. Based on the above studies, a mechanism involving a common intermediate (14) for the transformation of spiroketone (8 or 10) to either pyrrolotropone (9) or ester (12) depending on the substrate at the 1'-position has been suggested and further discussed in Section II. NaBH? and Zn/AcOH reductions of DDHQ/TCC esters are presented in Chapter IV. Synthesis and NaBH? reduction studies of various TCC and DDHQ esters (15) and (16) are discussed in Section I. It has been shown that TCC/DDHQ esters could be reduced specifically in the presence of alkyl/aryl esters. Isolation of a novel cycloheptatriene derivative (17) and 2-(2'-naphthofuryl)-dihydrocinnamic acid derivatives (18) in the reaction of DDHQ diesters with Zn–AcOH are discussed in Section III. Oxidation of (17) with CrO? gave tropone derivatives (19). The mechanism of this reaction is rationalised.