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Gandon LA, Russell AG, Güveli T, Brodwolf AE, Kariuki BM, Spencer N, Snaith JS. Synthesis of 2,4-Disubstituted Piperidines via Radical Cyclization: Unexpected Enhancement in Diastereoselectivity with Tris(trimethylsilyl)silane. J Org Chem 2006; 71:5198-207. [PMID: 16808507 DOI: 10.1021/jo060495w] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel approach to 2,4-disubstituted piperidines is reported, involving the radical cyclization of 7-substituted-6-aza-8-bromooct-2-enoates. Cyclization with tributyltin hydride affords the trans piperidines with trans/cis diastereomeric ratios ranging typically from 3:1 to 6:1. Cyclization with tris(trimethylsilyl)silane affords the same products with diastereomeric ratios of up to 99:1 in certain cases. The enhancement in diastereoselectivity results from the selective rearrangement of the minor stereoisomer through a cascade process involving radical cyclization to the piperidine radical, 1,5-radical translocation, and attack of the translocated radical onto the sulfonamide with extrusion of SO2 in a Smiles-type rearrangement. Slower trapping of the piperidine radical by tris(trimethylsilyl)silane compared to tributyltin hydride accounts for the occurrence of the rearrangement cascade in the former case.
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Affiliation(s)
- Lucile A Gandon
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K
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52
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de Figueiredo RM, Fröhlich R, Christmann M. N,N‘-Carbonyldiimidazole-Mediated Cyclization of Amino Alcohols to Substituted Azetidines and Other N-Heterocycles. J Org Chem 2006; 71:4147-54. [PMID: 16709054 DOI: 10.1021/jo060130b] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Amino alcohols are important synthons for N-heterocycles. We have developed an efficient method to activate hydroxyl groups, which avoids the use of toxic reagents and tolerates a wide variety of functional groups. Our strategy has been applied to the synthesis of functionalized p-methoxyphenyl-protected azetidines, pyrrolidines, and piperidines. The required amino alcohols were synthesized according to an optimized proline-catalyzed Mannich protocol. An azetidine analogue of ezetimibe was synthesized to demonstrate the potential for the synthesis of drug-like molecules.
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53
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Williams JT, Bahia PS, Kariuki BM, Spencer N, Philp D, Snaith JS. Synthesis of 3,4-Disubstituted Piperidines by Carbonyl Ene and Prins Cyclizations: Switching between Kinetic and Thermodynamic Control with Brønsted and Lewis Acid Catalysts. J Org Chem 2006; 71:2460-71. [PMID: 16526798 DOI: 10.1021/jo052532+] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel approach to cis and trans 3,4-disubstituted piperidines is described. Carbonyl ene cyclization of aldehydes 4a-e catalyzed by MeAlCl(2) in refluxing chloroform afforded the trans piperidines 7a-e with diastereomeric ratios of up to 93:7, while aldehyde 4f afforded solely the cis product 6f, which was resistant to isomerization to the trans isomer. It was demonstrated for 4a that the cyclization catalyzed by a variety of Lewis acids at low temperature proceeded under kinetic control to afford predominantly the cis piperidine 6a, and this isomerized to the thermodynamically more stable trans piperidine 7a on warming. In contrast, Prins cyclization of 4a-e catalyzed by concentrated hydrochloric acid in CH2Cl2 at low temperature afforded cis piperidines 6a-e with diastereomeric ratios of up to >98:2. The yield and diastereoselectivity of these cyclizations could be improved by using HCl-saturated CH2Cl2 to form the corresponding chloride, followed by elimination of HCl effected by ammonia. Aldehydes 4f and 4galso cyclized in good yield under the latter conditions. Mechanistic studies supported by DFT calculations (B3LYP/6-31G(d)) suggest that the cyclizations proceed via a mechanism with significant carbocationic character, with the cis carbocation being more stable than the trans carbocation. DFT calculations (B3LYP/6-31G(d)) of the transition state energies for concerted cyclization show that the cis piperidine is also the favored product from cyclization through a more concerted mechanism.
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Affiliation(s)
- Jodi T Williams
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
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54
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55
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The enantioselective synthesis of poison-frog alkaloids (−)-203A, (−)-209B, (−)-231C, (−)-233D, and (−)-235B″. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2005.11.047] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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56
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Chou SSP, Ho CW. Synthesis and transformations of sulfur-substituted indolizidines and quinolizidines. Tetrahedron Lett 2005. [DOI: 10.1016/j.tetlet.2005.09.191] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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57
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58
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Davis FA, Yang B. Asymmetric Synthesis of α-Substituted β-Amino Ketones from Sulfinimines (N-Sulfinyl Imines). Synthesis of the Indolizidine Alkaloid (−)-223A. J Am Chem Soc 2005; 127:8398-407. [PMID: 15941273 DOI: 10.1021/ja051452k] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Of the possible four stereoisomers, addition of the lithium enolate of 4-heptanone to sulfinimines resulted in only the syn- and anti-alpha-substituted beta-amino ketones. The formation of the major syn-beta-amino ketone was rationalized in terms of addition of the E-enolate to the C-N double bond of the sulfinimine via a six-member chelated chairlike transition state. The enolates of 4-heptanone were generated using LiHMDS in THF where a 1:2.5 E:Z enolate ratio was noted. In diethyl ether the E:Z ratio was 15:1 in favor of the E-enolate and explained in terms of Ireland's transition state model. Here increased steric interactions between the ethyl group and the carbonyl-LiN(TMS)(2) moiety destabilize the transition state leading to the Z-enolate in the poorly coordinating diethyl ether solvent. This new synthesis of syn-alpha-substituted-beta-amino ketones was applied to the concise enantioselective total synthesis of indolizidine (-)-223A, a 5,6,8-trisubstituted alkaloid isolated from the skin of the dendrobatide frog.
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Affiliation(s)
- Franklin A Davis
- Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
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59
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Michael JP, de Koning CB, van der Westhuyzen CW. Studies towards the enantioselective synthesis of 5,6,8-trisubstituted amphibian indolizidine alkaloids via enaminone intermediates. Org Biomol Chem 2005; 3:836-47. [PMID: 15731870 DOI: 10.1039/b418062c] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Investigations aimed at the enantioselective total synthesis of indolizidine 223A, a recently described 5,6,8-trisubstituted indolizidine alkaloid from a dendrobatid frog, are described. tert-Butyl (2R,3R)-3-amino-2-ethylhexanoate and its (2S,3R)-diastereomer, prepared in several steps from lithium N-benzyl-N-[(1R)-1-phenylethyl]amide and tert-butyl (2E)-hex-2-enoate by the Davies protocol, served as chiral building blocks from which two complementary suites of diastereomeric intermediates were made en route to pivotal tert-butyl 3-[2-(alkoxycarbonylmethylene)pyrrolidin-1-yl]-2-ethylhexanoate intermediates 20 and 21. Cyclisation of these enaminones, achieved by acid hydrolysis of the tert-butyl esters and activation of the liberated carboxylic acids as mixed anhydrides, afforded 6-ethyl-7-oxo-5-propyl-1,2,3,5,6,7-hexahydroindolizine-8-carboxylate esters 28 and 29. Several further transformations of these potential scaffolds for the synthesis of the target alkaloidal systems are also reported.
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Affiliation(s)
- Joseph P Michael
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg, P.O. Wits 2050, South Africa.
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60
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Chapter 6.1 Six-membered ring systems: Pyridines and benzo derivatives. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s0959-6380(05)80054-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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61
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Kumareswaran R, Gallucci J, Rajanbabu TV. Tuning the Acceptors in Catalyzed Cyclizations Initiated by Allenes. Silylstannylation/Cyclization of Allene-Aldehydes for Synthesis of Polyalkylated Indolizidines Including 223A Congeners. J Org Chem 2004; 69:9151-8. [PMID: 15609949 DOI: 10.1021/jo048580w] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Starting from succinamide and 1,2-heptadiene-4-ol, a racemic allene-aldehyde substrate, 20, suitable for R(3)SiSnR'(3)-mediated cyclization was synthesized in six steps and in 21% yield. Stereoselective cyclization (relative cis configuration at the new stereogenic centers of the homoallyl alcohol generated) proceeded smoothly, giving a mixture of indolizidinols bearing five contiguous stereocenters in a combined yield of 80%. Relative configurations of each of the products were unequivocally established by a combination of 2D NMR experiments and single-crystal X-ray analysis. The major indolizidinol obtained in 32% yield was elaborated into indolizidine 5,8-epi-indolizidine 223A via a five-step reaction sequence in 32% overall yield. The second major component (24%) of the key cyclization yielded, in four steps, indolizidine 6,8-epi-223 in 14% yield. Even though revision of the initially postulated structure foiled our original synthetic plans for the natural product, indolizidine 223A, the new stereoselective cyclization strategy and several selective transformations of the indolizidine derivatives reported here may find further applications for the synthesis of highly alkylated indolizidine and other related alkaloids.
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Affiliation(s)
- Ramaiah Kumareswaran
- Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, USA
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62
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Cassidy MP, Padwa A. An Aza-Achmatowicz Approach toward the Hydroxylated Piperidine Alkaloids (±)-Azimic Acid and (±)-Deoxocassine. Org Lett 2004; 6:4029-31. [PMID: 15496091 DOI: 10.1021/ol048326q] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] The synthesis of several cis-2,3,6-trisubstituted piperidines has been developed employing the aza-Achmatowicz oxidation as the key reaction step. Its usage is illustrated by the facile synthesis of the piperidin-3-ol alkaloids (+/-)-deoxocassine and (+/-)-azimic acid.
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Affiliation(s)
- Michael P Cassidy
- Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA
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63
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Uraguchi D, Sorimachi K, Terada M. Organocatalytic Asymmetric Aza-Friedel−Crafts Alkylation of Furan. J Am Chem Soc 2004; 126:11804-5. [PMID: 15382910 DOI: 10.1021/ja046185h] [Citation(s) in RCA: 313] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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.
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Affiliation(s)
- Daisuke Uraguchi
- Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
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64
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Dake GR, Fenster MDB, Hurley PB, Patrick BO. Synthesis of Functionalized 1-Azaspirocyclic Cyclopentanones Using Bronsted Acid or N-Bromosuccinimide Promoted Ring Expansions. J Org Chem 2004; 69:5668-75. [PMID: 15307738 DOI: 10.1021/jo0493572] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Azaspirocyclic ring systems are present in a variety of alkaloids. Functionalized 1-azaspirocyclopentanones (6, 7, 11, 12) can be efficiently constructed through semipinacol ring expansion reactions of 2-(1-hydroxycyclobutyl)-p-toluenesulfonylenamides (4) promoted by either a Bronsted acid ((S)-(+)-10-camphorsulfonic acid or HCl) or N-bromosuccinimide, an electrophilic bromine source. Reactions promoted by N-bromosuccinimide tend to proceed in higher yields (80-95%) and with greater diastereoselectivity (3:1-1:0) compared to those reactions promoted by a Bronsted acid. In addition, N-bromosuccinimide promoted reactions can produce a complementary stereochemical outcome compared to the reactions using Bronsted acid.
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Affiliation(s)
- Gregory R Dake
- Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1.
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65
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Stereodivergent synthesis of the 2,3,5,6-tetrasubstituted piperidine ring system: an application to the synthesis of alkaloids and from poison frogs. Tetrahedron 2004. [DOI: 10.1016/j.tet.2004.05.039] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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66
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Efficient asymmetric synthesis of α-(heteroaryl)alkylamines by 1,2-addition of lithiated hetarenes to aldehyde-SAMP-hydrazones. ACTA ACUST UNITED AC 2004. [DOI: 10.1016/j.tetasy.2003.12.036] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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67
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