Recent advances in the synthesis of piperidones and piperidines

Reactivity of cyclic sulfamidates towards sulfur-stabilised enolates. Stereocontrolled synthesis of functionalised lactams

A structurally representative series of 1,2- and 1,3-cyclic sulfamidates react with enolates derived from methyl alpha-phenylthioacetate 9b to give 5- and 6-substituted alpha-phenylthio lactams 20-24. These products provide, via the corresponding sulfoxides, an entry to alpha,beta-unsaturated lactams e.g. 12, 27, 29 and their alpha-phenylthio analogues e.g. 26 and 30. With the enantiomerically pure 1,2-cyclic sulfamidates 10, 15 and 17, these reactions all proceed with no detectable loss of stereochemical integrity.

A One-Pot Formal [4 + 2] Cycloaddition Approach to Substituted Piperidines, Indolizidines, and Quinolizidines. Total Synthesis of Indolizidine (−)-209I

[reaction: see text] Heating a mixture of substituted N-benzyl gamma-chloropropylamines, conjugated alkynoates or alkynones, sodium carbonate, and a catalytic amount of sodium iodide in i-PrOH at 70-83 degrees C delivers substituted piperidines in good yields. This transformation goes through a cascade Michael addition/alkylation process and represents a facile one-pot formal [4 + 2] cycloaddition approach to piperidine ring. Using secondary cyclic gamma-chloropropylamines as substrates, this process produces substituted indolizidines or quinolizidines. On the basis of this approach, indolizidine (-)-209I is elaborated in 11 steps from methyl 2-hexenoate.

Enantioselective Synthesis of 2-Aryl-4-piperidones via Rhodium/Phosphoramidite-Catalyzed Conjugate Addition of Arylboroxines

[reaction: see text] The highly enantioselective synthesis of 2-aryl-4-piperidones by rhodium/phosphoramidite-catalyzed conjugate addition of arylboroxines to 2,3-dihydro-4-pyridones is described. Both enantiomers of a variety of products with sterically and electronically different R substituents were obtained in high isolated yield and with excellent enantioselectivity up to 99%.

Recent advances in asymmetric synthesis of pipecolic acid and derivatives

This review covers the literature relating to asymmetric syntheses of pipecolic acid derivatives from 1997 to present. This review is organized according to the position and the degree of substitution of the piperidinic cycle. In a first section, syntheses of pipecolic acid itself are described. Then, successively, syntheses of C-3, C-4, C-5, C-6 substituted pipecolic acid derivatives are reported. Finally, syntheses of unsaturated pipecolic acid derivatives are presented before the last part devoted to the polysubstituted pipecolic acid derivatives.

Ruthenium-catalyzed enyne cycloisomerizations. Effect of allylic silyl ether on regioselectivity

The ruthenium-catalyzed cycloisomerization of 1,6- and 1,7-enynes substituted in the terminal allylic position with a tert-butyldimethylsilyl ether group emerges as an effective reaction to form unprecedented five- or six-membered rings possessing a geometrically defined enol silane. Straightforward synthetic access to a variety of achiral 1,6- and 1,7-enynes, as well as chiral ones, is presented. Ruthenium catalysts effect efficiently such single-step cycloisomerization at room temperature in acetone under neutral conditions. The cycloisomerization functions with (E) or (Z) 1,2-disubstituted alkenes. Parameters influencing the enol silane geometry are discussed. The level of selectivity depends on the alkyne substitution, the geometry of the double bond, and the nature of the catalyst. Furthermore, examples of stereoinduction are shown and lead to highly substituted carbo- and heterocycles with excellent diastereocontrol.

Convenient Synthesis of Substituted Piperidinones from α,β-Unsaturated Amides: Formal Synthesis of Deplancheine, Tacamonine, and Paroxetine

[reaction: see text] An intermolecular aza-double Michael reaction leading to functionalized piperidin-2-ones from simple starting materials has been developed. The method allows alpha,beta-unsaturated amides to be used as a synthon of the piperidine nucleus. In addition, the utility of this methodology is demonstrated by its application to a formal synthesis of the indolo[2,3-a]quinolizidine alkaloids, (+/-)-deplancheine, (+/-)-tacamonine, and the antidepressant paroxetine.

Catalytic enantioselective conjugate addition of dialkylzinc reagents to N-substituted-2,3-dehydro-4-piperidones

The first, highly enantioselective, copper/phosphoramidite-catalyzed conjugate addition of dialkylzinc reagents to N-substituted 2,3-dehydro-4-piperidones is described.

Detailed studies on the enantioselective synthesis and HPLC enantioseparation ofN-protected 3-hydroxyglutarimides

An analytical HPLC method using CHIREX (S)-LEU/(S)-alpha-NEA column was developed for the determination of the enantiomeric excesses of N-protected (S)-3-hydroxyglutarimides. Using this method, detailed studies on the base-promoted ring-expansion reaction of the amidolactones, derived from l-glutamic acid, were undertaken.

[5C + 1N] Annulation: a novel synthetic strategy for functionalized 2,3-dihydro-4-pyridones

A novel and facile route to functionalized mono/bicyclic 2,3-dihydro-4-pyridones has been developed via formal [5C + 1N] annulation of readily available alpha-alkenoyl ketene-(S,S)-acetals with various aliphatic primary amines.

Highly enantioselective dynamic kinetic resolution and desymmetrization processes by cyclocondensation of chiral aminoalcohols with racemic or prochiral δ-oxoacid derivatives

Cyclocondensation reactions of aminoalcohols and with racemic or prochiral delta-oxoacid derivatives provide polysubstituted lactams with high enantioselectivity in a process that involves dynamic kinetic resolution and/or desymmetrization of enantiotopic or diastereotopic ester groups.

Asymmetric hydrogenation of aromatic compounds

The asymmetric hydrogenation of aromatic and heteroaromatic compounds arguably presents one of the most attractive methods for the synthesis of six-membered cyclic compounds. In recent years, a number of promising stereoselective methods for the asymmetric hydrogenation of pyridines and related heterocycles have been reported.

Organocatalytic Asymmetric Aza-Friedel−Crafts Alkylation of Furan

A new asymmetric entry of the 1,2-aza-Friedel-Crafts reaction catalyzed by a chiral phosphoric acid is described. The present reaction has provided an atom-economical route to furan-2-ylamine derivatives in a highly enantioselective fashion. The synthetic utility of these products was displayed by oxidative cleavage of the furan ring (aza-Achmatowicz reaction) to form a 1,4-dicarbonyl compound that could be further derivatized to a chiral gamma-butenolid.

Synthesis of Enantiopure 4-Hydroxypipecolate and 4-Hydroxylysine Derivatives from a Common 4,6-Dioxopiperidinecarboxylate Precursor

tert-Butyl 2-substituted 4,6-dioxo-1-piperidinecarboxylates 4 have been prepared in good yield starting from Boc-Asp-O(t)Bu and other beta-amino acids. By analogy with chiral tetramic acids, their reduction by NaBH(4) in CH(2)Cl(2)/AcOH afforded the corresponding cis-4-hydroxy delta-lactams in good yield and stereoselectivity (68-98% de). In the absence of the A(1,3) strain (reduction of 6-substituted 2,4-dioxo-1-piperidines 7), the cis-4-hydroxy isomer was still obtained as the major product but the de values were consistently lower. 4-Hydroxy-6-oxo-1,2-piperidinedicarboxylate 2a, readily accessible from Boc-Asp-O(t)Bu (three steps, 63% overall yield), has proven to be an excellent building block for the synthesis of cis- and trans-4-hydroxypipecolates 17 and 24 (52 and 36% overall yield, respectively) and for the synthesis of a protected 4-hydroxylysine derivative 29 (41% overall yield).

Asymmetric Synthesis of Functionalized trans-2,6-Disubstituted Piperidines with N-Sulfinyl δ-Amino β-Ketoesters. Synthesis of (−)-Lasubine I

[reaction: see text] The hydroxy-directed reduction of 1,2-dehydropiperidines with the "ate" complex of DIBAL-H and n-BuLi affords functionalized trans-2,6-disubstituted piperidines. This methodology was employed in the asymmetric synthesis of the quinolizidine alkaloid (-)-lasubine I.