Transformed steroids. 123. Synthesis of 5α(H)- and 5α(OH)-6-ketosteroids with an additional 17α,20ξ-dihydroxytetrahydropyran ring E
The paper is devoted to the synthesis of 3,17α,20-trihydroxy-16β,23-epoxy-21,24-dinor-5αH-cholan-6-one and 3,5α,17α,20-tetrahydroxy-16β,23-epoxy-21,24-dinorcholan-6-one and derivatives of them. It has been shown that the reduction of 3,17α-dihydroxy-16β,23-epoxy-21,24-dinorchol-5-en-20-one with sodium tetrahydroborate and with diborane takes place stereospecifically with different spatial directivities: in the products of diborane reduction, ring E exists in the boat form, as has been shown by1H and13C NMR methods. The trans linkage of rings A/B in the modified steroids has been confirmed by their circular dichroism spectra.
Conformational analysis of 3-borabicyclo[3.3.1]nonane derivatives
Abstract Conformations of 3-borabicyclo[3.3.1]nonane derivatives have been studied by means of 1 H and 13 C NMR spectroscopy. With the aid of the coupling constants 3 J (HH) and 13 C chemical shifts it has been shown that all the derivatives of 3-borabicyclo[3.3.1]nonane with the trigonal boron atom studied are in a flattened double-chair conformation. In 3-borabicyclo[3.3.1]nonane derivatives with the tetra-coordinated boron atom and substituents at the 7α-position, the chair-boat conformation predominates, the boat conformation being characteristic of the cyclohexane ring; exceptions are the compounds with the internal donor—acceptor bond between the boron atom an 7α-substituent.
13C NMR spectroscopy of some 3- and 7-substituted bicyclo[3.3.1]nonanes
Abstract The 13 C NMR spectra of a series of 3,7-substituted bicyclo[3.3.1]nonane derivatives are examined. Taken into account substituent influences, the 13 C chemical shifts appear to be diagnostic for the conformation of the bicyclo[3.3.1]nonane derivative.