Jeremy S. Parker

Studies towards a postulated biomimetic Diels-Alder reaction for the synthesis of himgravine

Abstract The possible role of an iminium ion mediated Diels-Alder reaction on the biosynthetic pathway to himgravinc is discussed. The results of a preliminary investigation of a related oxycarbenium ion mediated Diels-Alder reaction are reported and are in accord with the stereochemistry of the natural product.

Concise Syntheses of the Natural Products (+)-Sylvaticin and (+)-cis-Sylvaticin

Two concise syntheses of the natural products cis-sylvaticin and sylvaticin are reported, using oxidative cyclization methodology as the key step. A sequential solvolysis/hydride shift/intramolecular reduction cascade was used to establish the trans stereochemistry of one of the THF rings of sylvaticin.

Manganese(III) acetate mediated oxidative radical cyclizations. Toward vicinal all-carbon quaternary stereocenters.

Manganese(III) acetate mediated oxidative radical cyclizations have been used to synthesize a range of densely functionalized and sterically congested cyclopentane-lactones. A number of the resulting lactones contain vicinal all-carbon quaternary stereocenters adjacent to a tertiary benzylic stereocenter and are formed with high levels of stereocontrol.

New Modes for the Osmium-Catalyzed Oxidative Cyclization

The osmium-catalyzed oxidative cyclization of amino alcohol initiators formally derived from 1,4-dienes is an effective method for the construction of pyrrolidines, utilizing a novel reoxidant (4-nitropyridine N-oxide = NPNO). The cyclization of enantiopure syn- and anti-amino alcohols gives rise to enantiopure cis- and trans-2,5-disubstituted pyrrolidines, respectively. Moreover, the cyclization of bis-homoallylic amines bearing an exocyclic chelating group is shown to be a complementary method for trans-pyrrolidine formation.

Asymmetric Reduction of Lactam-Based β-Aminoacrylates. Synthesis of Heterocyclic β2-Amino Acids

The ability to affect asymmetric reduction of heterocyclic β-aminoacrylates 1 (n = 1-3) has been assessed with pyrrolidine and piperidone variants generating the corresponding N-heterocyclic β(2)-amino acids 3b and 5b with high enantioselectivity (≥97% ee) using a Rh/WALPHOS catalyst combination. The use of the carboxylic acid substrate was essential; the corresponding esters do undergo reduction but led to racemic products. The seven-ring azepanone variant (as the carboxylic acid 9b) underwent reduction, but only a minimal level of asymmetric induction was observed.