Stereoselective synthesis of cis-2,6-disubstituted piperidines from 1,2-cyclic sulfamidates

Diastereoselective synthesis of cis-2,6-disubstituted piperidines from 1,2-cyclic sulfamidates is described. Regioselective ring-opening reactions of 1,2-cyclic sulfamidates derived from L-phenylalanine, alanine, valine, norvaline with the ketal protected acetylide with a phenyl substituent proceed smoothly to form the N-sulfamate intermediates which on acidic hydrolysis give alkynylated amines with the ketal group intact. Hydrogenation of the alkynylated amines, debenzylation, ketal deprotection, subsequent cyclization (of aminoketones) and stereoselective hydrogenation of the cyclic iminium ion intermediates afford the corresponding cis-2,6-disubstituted piperidines in high diastereoselectivity (98%?≥?d.e.) with good chemical yields (68–86%). The present approach provides a novel route for the stereoselective synthesis of cis-2,6-disubstituted piperidines.     

CATALYTIC DYNAMIC RESOLUTION APPLIED TO THE SYNTHESIS OF 2,6-DISUBSTITUTED PIPERIDINES: PREPARATION OF (+)-LUPETIDINE AND (-)-EPIDIHYDROPINIDINE

The diastereoselective synthesis of trans-2,6-disubstituted piperidines has been rendered enantioselective by incorporating a catalytic dynamic resolution into the first alkylation step. The method has been applied to the synthesis of (-)-epidihydropinidine and (+)-trans-lupetidine.     

A formal synthesis of psymberin

A formal synthesis of psymberin (irciniastatin A) is presented. Notable features of the synthesis include the chemo-, regio-, and stereoselective oxidation of a 1,3-disubstituted allene, a configuration-dependent spirodiepoxide opening, the efficient syntheses of functionalized trans-2,6-disubstituted pyrans, and the union of a highly functionalized aldehyde with a pentasubstituted aryl homoenolate to give a dihydroisocumarin. [structure: see text]     

BiBr3 initiated cyclization-addition reactions: effect of π-nucleophile on oxocarbenium ion addition and total syntheses of (+)-(S,S)-(cis-6-methyltetrahydropyran-2-yl)acetic acid and its trans-diastereomer

For BiBr₃ initiated tandem cyclization-additions of very reactive silyl ketene acetal nucleophiles with δ-silyloxy aldehydes to afford 2,6-disubstituted THP products, diastereoselectivities range from 5-6:1 (trans-/cis-). The selectivity for axial attack on the intermediate oxocarbenium ion is inversely proportional to π-nucleophilicity. We have utilized this chemistry to convert a common starting material to both cis- and trans-diastereomers of an acid first isolated from the secretions of Viverra civetta.     

Unprecedented observation of sulfonamides in the transesterification of N-unsubstituted carbamates with sulfonyl chlorides

Sulfonamides have been identified as by-products in the base-mediated transesterification of N-unsubstituted carbamates with sulfonyl chlorides to give the corresponding sulfonates. A proposed mechanism and the synthesis of hindered 2,6-disubstituted arylsulfonates via this method are also reported.     

Asymmetric synthesis of functionalized trans-2,6-disubstituted piperidines with N-sulfinyl delta-amino beta-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.     

Tandem overman rearrangement and intramolecular amidomercuration reactions. stereocontrolled synthesis of cis- and trans-2,6-dialkylpiperidines

[reaction: see text] Hg(II)-mediated tandem Overman rearrangement and intramolecular amidomercuration reactions were proven to provide a convenient tool for the stereoselective synthesis of cis- and trans-2,6-disubstituted piperidines. Thus, upon treatment with Hg(OTFA)(2) in THF, the trichloroacetimidate 1 directly transformed into the 2,6-dialkyl piperidine 2 with almost exclusive trans selectivity. The amiodomercuration reaction of the carbamate 7 by Hg(OTFA)(2) in nitromethane showed an excellent cis selectivity. Also reported is the stereoselective synthesis of solenopsin A and isosolenopsin A.     

Concise, stereocontrolled synthesis of the citrinadin B core architecture

A concise, stereocontrolled synthesis of the citrinadin B core architecture from scalemic, readily available starting materials is disclosed. Highlights include ready access to both cyclic tryptophan tautomer and trans-2,6-disubstituted piperidine fragments, an efficient, stereoretentive mixed Claisen acylation for the coupling of these halves, and further diastereoselective carbonyl addition and oxidative rearrangement for assembly of the core.     

An unexpected carbon dioxide insertion in the reaction of trans-2, 4-disubstituted azetidine, trans-2,5-disubstituted pyrrolidine, or trans-2,6-disubstituted piperidine with diphenylthiophosphinic chloride and diphenylselenophosphinic chloride

In the reaction of trans-2,4-disubstituted azetidine, trans-2, 5-disubstituted pyrrolidine, or trans-2,6-disubstituted piperidine with diphenylthiophosphinic chloride or diphenylselenophosphinic chloride in acetonitrile in the presence of potassium carbonate at room temperature, an unexpected carbon dioxide insertion produced carbamic diphenylthiophosphinic or diphenylselenophosphinic anhydride in good yield. The same product could be also obtained when the reaction was carried out under carbon dioxide atmosphere using potassium hydroxide or triethylamine as a base. This is a very simple reaction process related to the fixation of carbon dioxide without a metal catalyst.     

The Pauson-Khand reaction as a new entry to the synthesis of bridged bicyclic heterocycles: application to the enantioselective total synthesis of (−)-alstonerine

The first application of the Pauson-Khand reaction (PKR) to the synthesis of azabridged bicyclic structures is described. Compounds containing azabicyclo[3.3.1]nonane and azabicyclo[3.2.1]octane rings fused to cyclopentenones were efficiently constructed via the PKR of cis-2,6-disubstituted N-acyl piperidine enyne substrates, many of which can be readily prepared from 4-methoxypyridine in a few steps. Moreover, the PKR of cis-2,6-disubstituted piperazine enynes allowed the preparation of diazabicyclo[3.3.1]nonanes fused to cyclopentenones. This new strategy for the synthesis of azabridged bicyclic frameworks was exploited as a key step in a concise, enantioselective total synthesis of the macroline alkaloid (−)-alstonerine.     

A practical asymmetric synthesis of 2,6-cis-disubstituted piperidines

A highly diastereoselective intramolecular Mannich reaction involving enantiopure α-methylamine 7 and achiral aldehydes is employed to prepare enantiomerically pure 2,6-cis-disubstituted piperidines. This methodology provides an efficient and selective route to 2,6-cis-disubstituted piperidines, 2,6-cis-disubstituted 4-piperidones and 2,6-cis-disubstituted 4-piperidinols.     

A new, enantioselective synthesis of (+)-isolaurepan

A highly enantioselective synthesis of 2,6-syn-disubstituted tetrahydropyrans from commercially available tri-O-acetyl-d-glucal, based on a thermal Claisen rearrangement, allows enantioselective synthesis of (+)-isolaurepan when combined with a ring expansion reaction using trimethylsilyldiazomethane.     

Stereocontrolled approach to 1-azabicyclo[4.1.0]heptanes: application to the synthesis of trans-2,6-disubstituted piperidines

Stereocontrolled synthesis of a 1-azabicyclo[4.1.0]heptane is achieved by formation of an NH aziridine from the corresponding 1,2-azido alcohol and subsequent intramolecular conjugate addition onto a tethered α,β-unsaturated ester. Regioselective ring opening of the product at C-7 by heteroatom based nucleophiles yields trans-2,6-disubstituted piperidines in moderate to good yields.     

Asymmetric synthesis of ring functionalized trans-2,6-disubstituted piperidines from N-sulfinyl delta-amino beta-keto phosphonates. total synthesis of (-)-myrtine

Sulfinimine-derived N-sulfinyl delta-amino beta-ketophosphonates are transformed via the enaminones to the phosphoryl dihydropyridones that selectively give trans-2,6-disubstituted 1,2,5,6-tetrahydropyridines on organocuprate addition and dephosphorylation.     

Synthesis and biological evaluation of 12-, 13-, 14-membered macrolides and open chain 2,6-trans-disubstituted dihydropyran analogues for aspergillides

Stereoselective synthesis of twenty (three 12-, five 13- and twelve 14-membered) macrolides and seventeen functionalized 2,6-trans-disubstituted dihydropyran derivatives have been achieved. The key reactions include an Achmatowicz rearrangement, Ferrier-type alkynylation, Yamaguchi macrolactonization and Lindlar’s hydrogenation. Biological screening of the synthesised compounds showed moderate activity against human cancer cell-lines.     

Diastereoselective Synthesis of cis-2,6-Disubstituted Perhydro-4-pyranones Using Elevated Pressure Hydrogenation

A diastereoselective strategy for the synthesis of γ-pyrons was developed, starting from the Mg diacetonedicarboxylate complex. Initial cyclization with suitable anhydrides or acid chlorides, followed by hydrolytic decarboxylation leads to 2,6-disubstituted pyrans. Elevated pressure hydrogenation using Pd/C affords the title compounds in high diastereoselectivity. Scope and limitations of the method are outlined on selected examples.     

Enantiocontrolled synthesis of 2,6-disubstituted piperidines by desymmetrization of meso-eta-(3,4,5)-dihydropyridinylmolybdenum complexes. application to the total synthesis of (-)-dihydropinidine and (-)-andrachcinidine

A conceptually new approach to the enantiocontrolled synthesis of 2,6-disubstituted piperidines was achieved by desymmetrization of meso-2,6-dimethoxy-eta-(3,4,5)-dihydropyridinylmolybdenum complexes. After protection of the piperidine nitrogen as a urethane derived from (+)- or (-)-trans-2-(alpha-cumyl)cyclohexyl (TCC), a sequential, one-pot methoxide abstraction/nucleophilic addition/methoxide abstraction/nucleophilic addition generated good yields of 2,6-disubstituted-eta-(3,4,5)-dihydropyridinylmolybdenum complexes. This sequence proceeds by way of a highly diastereoselective methoxide abstraction (>40:1). High yielding protodemetalation and N-deprotection provided a simple and enantiocontrolled synthetic entry to a variety of 2,6-disubstituted piperidines. This new method was used for the total synthesis of (-)-dihydropinidine and (-)-andrachcinidine.     

Convergent total synthesis of (−)-dactylolide

A convergent total synthesis of (?)-dactylolide is described. Constructing the 2,6-disubstituted exo-methylene THP moiety was achieved by the intramolecular allylation of α-acetoxy ether. The cyclization precursor was prepared from two segments, an alcohol and carboxylic acid derivatives, by esterification followed by reductive acetylation.     

Preparation of γ-trimethylsilylallyldibutylstannane grafted on solid support: a clean and easily recyclable reagent for the synthesis of 2,6-disubstituted dihydropyrans

The synthesis of the γ-trimethylsilyldibutylallylstannane grafted on an insoluble macroporous polymer is reported. This bimetallic reagent was treated with aldehydes in the presence of indium trichloride to afford in good yields both symmetrical and unsymmetrical cis-2,6-disubstituted dihydropyrans, practically uncontaminated with organotin residues (less than 20 ppm). The potential for regeneration and reuse of this supported bimetallic reagent is pointed out.     

An asymmetric synthesis of (+)-desoxoprosophylline

An efficient synthesis of (+)-desoxoprosophylline is described. The key steps in the reaction sequence include the preparation of an N-Cbz-sulfilimine from the corresponding sulfoxide using the Burgess reagent, regio- and stereoselective hetero-functionalization of an alkene using the pendant sulfilimine as the nucleophile and a stereoselective amidomercuration to form the cis-2,6-disubstituted piperidine ring.