One-pot tandem reactions for the stereoselective synthesis of functionalised carbocycles

摘要

A one-pot, two step tandem process involving an Overman rearrangement and a ring closing metathesis reaction has been utilised for the efficient synthesis of various cyclic allylic trichloroacetamides from simple allylic alcohols. Various methods were then investigated for the allylic oxidation of a carbocyclic amide using TBHP along with different transition metals such as Pd, Se, Mn and Cr. This was required for the synthesis of the important building blocks for the construction of structurally diverse antiviral and anticancer carbocyclic nucleosides and natural products. The oxidation of (1S)-N-(cyclohexenyl)trichloroacetamide was then studied leading to the preparation of two diol analogues in excellent stereoselectivity. The cyclohexene derivative was also stereoselectively functionalised using Upjohn dihydroxylation conditions or by a directed epoxidation/hydrolysis sequence of reactions to generate two aminocyclitols, the enantiomer of dihydroconduramine C-1 and dihydroconduramine E-1 in excellent stereoselectivity. In addition to this, a one-pot tandem process involving a substrate-directed Overman rearrangement and ring closing metathesis reaction was developed for the stereoselective synthesis of a functionalised carbocyclic allylic trichloroacetamide. The functionalised carbocyclic amide was employed in the successful synthesis of a syn-(4aS,10bS)- phenanthridone framework using a Pd-catalysed cross-coupling reaction. Stereoselective epoxidation and dihydroxylation of the syn-(4aS,10bS)-phenanthridone was then investigated leading to the preparation of new analogues of 7-deoxypancratistatin. Attempts were also made to use the functionalised carbocyclic amide in the total synthesis of the Amaryllidaceae alkaloid (+)-γ-lycorane. Further studies were then investigated to expand the scope of the one-pot tandem process to include heterocyclic derived substrates. This led to a seven-membered carbocyclic amide, which has been modified to create a diastereomeric core of balanol.