Investigation towards the total synthesis of b-secosteroids

Abstract

The thesis entitled “Investigations Towards the Total Synthesis of B Secosteroids” consists of two parts. Part I describes:

the synthesis of a few mono and dimethoxy 5/8 seco 5/7 bisnor steroids (Chapter I), and a study of acid catalysed cyclisations of B secosteroidal intermediates (the seco diones) to understand: i) the modified reactivity of the styrene double bond as a function of various substitutions on the phenyl ring and the nature of the alkyl side chains, ii) the reactivity of the seco diones with respect to various reagent–solvent combinations, iii) the mechanism of formation of various products under different reaction conditions, and iv) the generality of MeOH–HCl as a reagent to obtain the C 2 substituted isomeric exo and endo bicyclo[3.2.1]octane 6,8 diones (Chapter II).

During these studies, the role of protic and aprotic solvents in determining product formation was clearly demonstrated. These studies were extended to the aliphatic counterparts of the seco diones (Chapter III). In these acid catalysed cyclisation reactions, a number of mechanistically as well as structurally interesting compounds were isolated and characterised from their spectral data.

Part II Part II deals with the detailed analysis of ¹H NMR (Chapter I), ¹³C NMR (Chapter II), and mass spectra (Chapter III) of C 2 substituted isomeric exo and endo 5 methylbicyclo[3.2.1]octane 6,8 diones, for complete structural and configurational assignment. During these studies, it was observed that:

the chemical shifts of various protons (in ¹H NMR) and of carbon atoms (in ¹³C NMR) can be used to differentiate such isomeric compounds, and methoxy substitution on the phenyl ring has a considerable effect on the shielding of neighbouring atoms.