Selective routes to substituted dihydropyridones

Thesis

Introduction: The introduction provides a survey of the natural product and pharmaceutical targets accessible from dihydropyridines and dihydropyridones as well as an overview of previous work carried out towards the synthesis of these valuable intermediates. The mechanism, scope and limitations of the various approaches are covered, along with the goals of this project.

Results and Discussion: A Regioselective Route to Dihydropyridones. The regioselective addition of nucleophiles to a range of disubstituted pyridinium salts has been achieved, with selectivity determined by hard/soft factors. Certain nucleophiles can be added with complete regioselectivity to either C-2 or C-6 of these salts, depending on the conditions employed. Addition at C-2 allows the generation of a quaternary centre in high yield. The conditions discovered can be applied to pyridinium salts with different substitution patterns and an effective procedure has been developed for the removal of the nitrogen protecting group post reduction.

The Preparation of Enantiopure Dihydropyridones.After unsuccessful attempts to find a reagent-controlled asymmetric synthesis of dihydropyridones, a highly diastereoselective and non-chiral auxiliary based substrate-controlled procedure has been developed. By prompting an intramolecular hydride migration from a secondary silyl ether onto the pyridinium core, the corresponding dihydropyridones are available in high yield, with the diastereoselectivity being controlled by the minimization of 1,3-allylic strain between the N-allyl group and the hydride-bearing side chain. Thus, an enantiopure pyridyl alcohol may be converted to the corresponding dihydropyridone without loss of enantiomeric purity. Furthermore, the dihydropyridones can be easily converted to complex bicyclic systems via a ring closing metathesis reaction.

Experimental: Full experimental procedures and spectroscopic characterization of compounds are provided.

Authors: Connolly, M; Matthew James Connolly

• Publication date: 2011
• DOI: 10.5287/ora-xq4o7xq8x
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: pyridines; asymmetric synthesis; dihydropyridones; reduction
• Subjects: Organic chemistry; Synthetic organic chemistry; Organic synthesis