Access to 2,6-Disubstituted Piperidines: Control of the Diastereoselectivity, Scope, and Limitations. Applications to the Stereoselective Synthesis of (−)-Solenopsine A and Alkaloid (+)-241D

A Unified Synthesis of Electron-Deficient 1,4- and 1,1,4-Substituted 1,3-Dienes through a Base-Promoted Allylation Followed by Retro-Michael Vinylogous Dehydrosulfinylation

We disclose a general 2-step synthesis of electron-poor 1,4- and 1,1,4-substituted buta-1,3-dienes bearing electron-withdrawing substituents at both termini of the conjugated system. The method relies on a base-promoted C-allylation of primary or secondary alkylsulfones with γ-bromocrotonate or related amide, nitrile, or sulfone and subsequent vinylogous retro-Michael dehydrosulfinylation. The geometry of the resulting dienes is substrate-dependent, and predominantly E,E-dienes are formed from E-electrophiles. This phosphorus- and transition-metal-free method tolerates a variety of functionalities and could serve as a supplement to Wittig, HWE, and Julia olefinations.

Addition of Lithium Anion of (Acetylmethylene)triphenylphosphorane to Nonracemic Sulfinimines: Total Synthesis of (+)-241D and Formal Total Synthesis of (+)-Preussin

The addition of lithium anion of (acetylmethylene)triphenylphosphorane to nonracemic sulfinimines was investigated. It was found that the addition proceeded with good diastereoselectivity and further reaction of the formed sulfinimidophosphorane with several aldehydes afforded the β-sulfinamido substituted enones in good yields. The resultant enones were elaborated to the synthesis of alkaloid (+)-241D, to the formal total synthesis of (+)-preussin, and to the synthesis of aminocyclopentenol.

Stereoselective synthesis of 2,6-disubstituted piperidine alkaloids

Among the large number of structurally diverse alkaloids, 2,6-disubstituted piperidine and its analogs have often been targeted when exploiting new synthetic techniques perhaps because of their strong pharmacological properties. This review outlines synthetic strategies to build the 2,6-disubstituted piperidine structural motif with a focus on stereochemical control of two substituents at C2 and C6. The key reactions in this process are then classified on the basis of how the piperidine rings were built with specific examples of natural products that control the stereochemical outcomes and their transition states.

The endo-aza-Michael addition in the synthesis of piperidines and pyrrolidines

Intramolecular endo-aza-Michael additions are categorised in various ways.

Enantiodivergent Approach to the Synthesis of Cis-2,6-Disubstituted Piperidin-4-ones

Enantiopure β-amino ketone derivatives were synthesized by decarboxylative Mannich reaction of chiral N- tert-butanesulfinyl imines with β-keto acids and were subsequently transformed into cis-2,6-disubstituted piperidin-4-ones through an organocatalyzed condensation with aldehydes. Both enantiomers were accessible from the same precursors by inverting the order in the reaction sequence of the aldehydes involved in the imine formation and the intramolecular Mannich condensation. The synthesis of the piperidine alkaloids (+)-241D, (-)-epimyrtine, and (-)-lasubine II demonstrated the utility of this methodology.

Stereoselective synthesis of 2,6-trans-4-oxopiperidines using an acid-mediated 6-endo-trig cyclisation

An acid-mediated 6-endo-trig cyclisation of amine-substituted enones has been developed for the stereoselective synthesis of trans-6-alkyl-2-methyl-4-oxopiperidines. Performed under conditions that prevent removal of the Boc-protecting group or acetal formation, the key cyclisation was found to generate cleanly the 4-oxopiperidine products in high overall yields from a wide range of alkyl substituted enones. The synthetic utility of the trans-6-alkyl-2-methyl-4-oxopiperidines formed from this process was demonstrated with the total synthesis of the quinolizidine alkaloid, (+)-myrtine and the piperidine alkaloid, (-)-solenopsin A.

Access to 2,6-Disubstituted 4-Oxopiperidines Using a 6-Endo-trig Cyclization: Stereoselective Synthesis of Spruce Alkaloid and (+)-241D

A synthetic route to cis-2-methyl-4-oxo-6-alkylpiperidines has been developed using a 6-endo-trig cyclization of (E)-enones. The base-mediated intramolecular cyclization was found to be general for both alkyl- and aryl-substituted enones, providing the corresponding 4-oxopiperidines in high yields (80-89%). Stereoselective reduction of the 2,6-cis-disubstituted 4-oxopiperidines then gave the 2,4,6-cis,cis-trisubstituted 4-hydroxypiperidines in high diastereoselectivity. The general nature of this approach was demonstrated with the synthesis of the natural products, spruce alkaloid and (+)-241D.

Stereoselective strategies for the construction of polysubstituted piperidinic compounds and their applications in natural products’ synthesis

An abridged and far-reaching review communication on the construction of the polysubstituted piperidinic core using diverse methodologies for the benefit of organic chemists interested in the total synthesis of biologically active compounds.

Synthesis of β-Amino-Substituted Enones by Addition of Substituted Methyl Enones to Sulfinimines: Application to the Total Synthesis of Alkaloids (+)-Lasubine II and (+)-241D and the Formal Total Synthesis of (-)-Lasubine I

Addition of silyl enol ethers obtained from substituted methyl enones to chiral sulfinimines afforded the β-amino-substituted enones with excellent selectivity. Utility of the obtained N-sulfinyl β-amino ketones possessing α,β-unsaturation is exemplified in the total synthesis of the quinolizidine alkaloid natural products (-)-lasubine I, (+)-lasubine II, and substituted piperidine alkaloid (+)-241-D.

One-pot multiple reactions: asymmetric synthesis of 2,6-cis-disubstituted piperidine alkaloids from chiral aziridine

A divergent, new, and highly stereoselective synthesis of cis-2,6-disubstituted piperidine natural products including isosolenopsins, deoxocassine, and spectaline was achieved from chiral aziridine decorated with appropriate alkyl chains for isosolenopsins or alkynyl groups for deoxocassine and spectaline at C2. The characteristic feature of this synthesis is one-pot sequential reactions under atmospheric hydrogen including the reduction of alkyne (for deoxocassine and spectaline), reductive ring-opening of aziridine, debenzylation, and intramolecular reductive amination in high yields. The prerequisite aziridines were elaborated from commercially available (2S)-hydroxymethylaziridine through oxidation, Wittig olefination, and the Grignard reaction for isosolenopsins or substrate-controlled lithium alkynylate addition for deoxocassine and spectaline.

Nature-inspired enzymatic cascades to build valuable compounds

Biocatalysis currently is focusing on enzymatic and multi-enzymatic cascade processes instead of single steps imbedded into chemical pathways. Alongside this scientific revolution, this review provides an overview on multi-enzymatic cascades that are responsible for the biosynthesis of some terpenes, alkaloids and polyethers, which are important classes of natural products. Herein, we illustrate the development of studies inspired by multi- and chemo-enzymatic approaches to build the core moieties of polyethers, polypeptide alkaloids, piperidines and pyrrolidines promoted by the joint action of oxidoreductases, hydrolases, cyclases, transaminases and imine reductases.

Building polyfunctional piperidines: a stereoselective strategy of a three-component Mannich reaction inspired by biosynthesis and applications in the synthesis of natural alkaloids (+)-241D; (−)-241D; isosolenopsin A and (−)-epimyrtine

A stereoselective strategy for building polyfunctional piperidines by a three-component Mannich reaction and applications in the stereoselective synthesis of natural alkaloids.

Direct access to functionalized benzotropones, azepanes, and piperidines by reductive cross-coupling of α-bromo enones with α-bromo enamides

High-yielding syntheses of functionalized azepenes and piperidines, bearing an α-benzotropone derivative, have been achieved through cobalt-catalysed reductive cross-coupling of α-bromo enamides with α-bromo enones.

A concise diastereoselective approach to enantioenriched substituted piperidines and their in vitro cytotoxicity evaluation

A library of diversely stereo-oriented, highly substituted 2,6-cis piperidine derivatives were synthesized, and evaluated for their anticancer activity in cancer cells that included A549 (lung cancer, CCL-185), MCF7 (breast cancer (HTB-22), DU145 (prostate cancer (HTB-81), and HeLa (cervical cancer, CCL-2). One stereo-variant emerged as a promising candidate for further design based structure-activity studies.