Grignard addition to 1-acyl salts of chiral 4-alkoxypyridines. A new enantioselective preparation of 2-alkyl-2,3-dihydro-4-pyridones

Synthesis of 1,3-amino alcohol derivatives via a silicon-mediated ring-opening of substituted piperidines

Multisubstituted piperidines containing a trimethylsilylmethyl group at C-2 can be opened regioselectively with TBAF and cyanogen bromide. The ring-opened products contain synthetically useful cyanamide and terminal alkene functional groups. This method is useful for the stereoselective synthesis of alkylamine derivatives containing multiple chiral centers.

N-acyldihydropyridones as synthetic intermediates. A stereoselective synthesis of acyclic amino alcohols containing multiple chiral centers

Various multisubstituted piperidines containing a phenyl group at C-2 can be opened regio- and stereoselectively with cyanogen bromide. The ring-opened products contain useful cyanamide and benzylic bromide functional groups. The benzyl bromide can be cleanly reduced, or substituted with various nucleophiles via an S(N)2 process to add additional heteroatoms stereoselectively. This methodology is useful for the stereoselective synthesis of uniquely substituted alkylamine derivatives containing multiple chiral centers and various functionality. Diastereomerically pure amino alcohols containing three to five contiguous stereocenters were prepared using this strategy.

Diels-Alder reactions of N-acyl-2-alkyl(aryl)-5-vinyl-2,3-dihydro-4-pyridones

Readily available N-acyl-5-vinyl-2,3-dihydro-4-pyridones undergo Diels-Alder cyclization with various dienophiles to afford novel octahydroquinolines containing synthetically useful functionality. With dihydropyridone 5 and cis-disubstituted dienophiles, the resulting cycloadducts were obtained as single diastereomers in good to excellent yield. The corresponding reaction of 5 with methyl acrylate, acrylonitrile, and phenyl vinyl sulfone showed modest preference for the endo adducts. The effect of the dihydropyridone C-2 and C-4 substituents on the degree of diastereofacial control was examined. By using this methodology, the core decahydroquinoline skeleton of gephyrotoxin was prepared in a stereocontrolled fashion. Interesting reactivity was observed with certain dienophiles leading to ring-opening of the initially formed cycloadducts. This tandem reaction provides a route to uniquely substituted beta-aminoketones, alcohols, and unnatural amino acids.

Diels-Alder reactions of 5-vinyl-1-acyl-2-aryl-2,3-dihydro-4-pyridones: regio- and stereoselective synthesis of octahydroquinolines

[reaction: see text] Readily available 5-vinyldihydropyridones 2 undergo Diels-Alder cyclization with various dienophiles to afford novel octahdroquinolines. The process is highly stereoselective and provides heterocyclic products containing synthetically useful functionality.

The Mukaiyama-Michael reaction of N-acyl-2,3-dihydro-4-pyridones: regio- and stereoselective synthesis of cis-2,6-disubstituted 1,2,5,6-tetrahydropyridines

[formula: see text] A convenient regio- and stereoselective preparation of 1,2,5,6-tetrahydropyridines of the type 1 has been developed, starting from readily available N-acyl-2,3-dihydro-4-pyridones 2.

Article

Alkylation of the hippurate esters of trans 2-(p-substituted phenyl)cyclohexanol with benzyl bromide affords phenylalanine derivatives in high chemical yield. The reaction stereoselectivity varies from 20 to >98% depending on the aromatic group in the cyclohexyl auxiliary. A model that correctly predicts the sense of the induction is proposed.Key words: enolate conformation, pi-stacking, 2-phenylcyclohexanol, chiral auxiliary.