Highly Efficient Synthesis of Tricyclic Amines by a Cyclization/Cycloaddition Cascade: Total Syntheses of Aspidospermine, Aspidospermidine, and Quebrachamine

Coldham, Iain; Burrell, Adam J. M.; White, Laura E.; Adams, Harry; Oram, Niall

doi:10.1002/anie.200701943

Cited by 98 publications

(26 citation statements)

References 51 publications

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“…1 However, few examples of tropane or indolizidine synthesis by [3 + 2] cycloaddition between an azomethine ylide and a dipolarophile have been reported, and this is particularly true for unstabilized ylides. 2 While azomethine ylide cycloadditions represent a powerful strategy for the convergent assembly of five-membered nitrogen heterocycles, 3,4 only simple unstabilized ylides have primarily been used due to the challenges associated with generating more complex and highly substituted derivatives.…”

Section: Introductionmentioning

confidence: 99%

New Regio- and Stereoselective Cascades via Unstabilized Azomethine Ylide Cycloadditions for the Synthesis of Highly Substituted Tropane and Indolizidine Frameworks

et al. 2016

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Multisubstituted tropanes and indolizidines have been prepared with high regio- and stereoselectivity by the [3 + 2] cycloaddition of unstabilized azomethine ylides generated from readily prepared trimethylsilyl substituted 1,2-dihydropyridines via protonation or alkylation followed by desilylation. Starting from 1,2-dihydropyridines bearing a ring trimethylsilyl substituent at the 6-position, an intermolecular alkylation/desilylation provides endocyclic unstabilized ylides that successfully undergo cycloaddition with a range of symmetrical and unsymmetrical alkyne and alkene dipolarophiles to afford densely substituted tropanes incorporating quaternary carbons in good yields and with high regio- and stereoselectivity. Additionally, an intramolecular alkylation/desilylation/cycloaddition sequence provides convenient and rapid entry to bridged tricyclic tropane skeletons, allowing for five contiguous carbon stereocenters to be set in a single experimental operation and under mild conditions. Starting from 1,2-dihydropyridines with trimethylsilylmethyl groups on nitrogen, protonation followed by desilylation generates exocyclic unstabilized ylides that undergo cycloaddition with unsymmetrical alkynes to give indolizidines with good regio- and stereoselectivity. N-Trimethylsilylmethyl 1,2-dihydropyridines can also be alkylated and subsequently desilylated to give endocyclic unstabilized ylides that undergo intermolecular cycloadditions with carbonyl compounds to give bicyclic oxazolidine products in good overall yields. Moreover, an intramolecular alkylation/desilylation/cycloaddition sequence with the N-trimethylsilylmethyl 1,2-dihydropyridines affords tricyclic indolizidines that incorporate quaternary carbons and up to five stereocenters with good to excellent regio- and diastereoselectivity.

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Section: Introductionmentioning

confidence: 99%

New Regio- and Stereoselective Cascades via Unstabilized Azomethine Ylide Cycloadditions for the Synthesis of Highly Substituted Tropane and Indolizidine Frameworks

et al. 2016

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“…Motivated by their bioactivities and attractive polycyclic structures, enormous synthetic studies on this class of compounds have been carried out. [3][4][5][6][7][8][9] Since the bond formation between the indole and the terpenoid moiety had been well resolved, much effort has been made to enhance the stereoselective construction of the quaternary carbon. Among these studies, strategies based on chiral auxiliary are dominant, and catalytic enantioselective method remains as a challenging task.…”

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confidence: 99%

Toward General Access to the <i>Aspidosperma</i>-Type Terpenoid Indole Alkaloids: Synthesis of the Key 3,3-Disubstituted Piperidones through Enantioselective Intramolecular Heck-Type Reaction of Chloroformamides

2008

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An enantioselective intramolecular Heck-type reaction of chloroformamides has been developed for the synthesis of 3,3-disubstituted piperidones. The desired piperidone was formed in the presence of a palladium catalyst, an optically active phosphoramidite ligand, K 3 PO 4 and Ag 3 PO 4 . The obtained piperidone was converted to epieburnamonine.Key words enantioselective reaction; total synthesis; terpenoid indole alkaloid Chem. Pharm. Bull. 56(11) 1567-1574 (2008) © 2008 Pharmaceutical Society of Japan * To whom correspondence should be addressed. e-mail: takemoto@pharm.kyoto-u.ac.jp under normal conditions (entries 1-3). However, lactam 9 was isolated in 60% yield when Ag 3 PO 4 was added to the reaction (entry 4). The combination of Pd 2 (dba) 3 and BINAP was also able to promote the cyclization in the presence of Ag 3 PO 4 (entry 5). Nolan's NHC catalyst was not effective (entry 6).With these results in hand, syntheses of each cis-trans isomer of alkenyl chloroformamide 2 were performed. Alkene (E)-4 was synthesized through hydroalumination as a key step (Fig. 5). 4-Pentyn-1-ol (10) was transformed into alcohol 11 through oxidation, acetalization, and hydroxymethylation using benzotriazolylmethanol (BtCH 2 OH). 22) Alcohol 11 was then subjected to the hydroalumination-iodination sequence 23,24) to give (Z)-iodo alkene 12, whose configuration was confirmed by NOE experiment. Ethylation by Suzuki coupling, followed by benzylation gave the desired alkene (E)-4.Change of the starting material afforded the alternative stereoisomer (Fig. 6). (Z)-Iodoalkene 14 was synthesized from 2-pentyn-1-ol (13) through hydroalumination and iodination. Since benzylation of the hydroxy group under either basic or acidic conditions competed with decomposition of the starting material, protection by THP group was carried out. The resultant THP ether 15 underwent Negishi coupling with 3,3-(dimethoxy)propylzinc chloride 16. 25) Selective hydrolysis of the THP ether and benzylation afforded the desired alkene (Z)-4.Alkenyl acetals (E)-4 and (Z)-4 were coupled with tryptamine 3 26) through hydrolysis and reductive amination to give amines (E)-17 and (Z)-17, respectively (Fig. 7). These compounds were converted to the corresponding chloroformamides (E)-2 and (Z)-2 by treating with triphosgene and Et 3 N.Before the enantioselective Heck-type reaction, a racemic reaction was attempted to find out a suitable palladium source ( Table 2). The cyclized product 1 was isolated after hydrolysis of the resultant enol ether. At the early stage, poor reproducibility was a serious problem. After several attempts, it was found that the activity of the catalyst is highly associated with the conditions used to mix palladium sources and ligands prior to the addition of chloroformamide 2. When [Pd(h 3 -C 3 H 5 )Cl] 2 was premixed with (p-tol) 3 P at 30°C for 30 min, the disappearance of 2 was slow and the yield was 30% after 24 h (entry 1). In contrast, the starting material disappeared in 3 h and yield reached 49% when premixing was performed at 40°C...

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“…The stereochemistry of the obtained products 16a-e was established on the basis of spectral data, and by comparison with similar systems. 8,11 Further more, boiling the cycloadduct 16a in dry methanol saturated with HCl gas for 4h afforded a quantitative yield of the trimethyl tricarboxylate ester 18 (Scheme 5). The stereochemistry of 18 was assigned on the basis of spectral data, and by comparison with similar systems.…”

Section: Methodsmentioning

confidence: 99%

Stereospecific non-decarboxylative 1,3-dipolar cycloaddition as a potential route for the synthesis of some proline derivatives, part (III)

Aly¹,

Abbas-Temirek²,

Elboray³

2009

Arkivoc

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Highly Efficient Synthesis of Tricyclic Amines by a Cyclization/Cycloaddition Cascade: Total Syntheses of Aspidospermine, Aspidospermidine, and Quebrachamine

Cited by 98 publications

References 51 publications

New Regio- and Stereoselective Cascades via Unstabilized Azomethine Ylide Cycloadditions for the Synthesis of Highly Substituted Tropane and Indolizidine Frameworks

New Regio- and Stereoselective Cascades via Unstabilized Azomethine Ylide Cycloadditions for the Synthesis of Highly Substituted Tropane and Indolizidine Frameworks

Toward General Access to the <i>Aspidosperma</i>-Type Terpenoid Indole Alkaloids: Synthesis of the Key 3,3-Disubstituted Piperidones through Enantioselective Intramolecular Heck-Type Reaction of Chloroformamides

Stereospecific non-decarboxylative 1,3-dipolar cycloaddition as a potential route for the synthesis of some proline derivatives, part (III)

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