Palladium-Catalyzed Intramolecular Cyanoamidation of Alkynyl and Alkenyl Cyanoformamides

Kobayashi, Yusuke; Kamisaki, Haruhi; Yanada, Reiko; Takemoto, Yoshiji

doi:10.1021/ol060733+

Cited by 131 publications

(35 citation statements)

References 18 publications

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“…14) Scope of this reaction is a limitation on the substrates: usually, the reaction needs to start from aryl or vinyl halides. In context of our recent studies on transition-metalcatalyzed reactions of carbamoyl derivatives, [15][16][17][18] we planned to develop an enantioselective Heck-type reaction of carbamoyl chlorides (Fig. 2b).…”

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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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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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“…The same reaction of acetate 7b and silyl ether 7c did not give good results (entries 3, 4). However, 2-methoxy-2-propyl (MOP) derivatives 7d and 7d 0 underwent hydroamidation to give lactams 6a and 6a 0 in high yields after unexpected cleavage of the MOP group (entries 5,6). It is likely that the MOP group was cleaved after cyclization because of the clear difference between the yields of entries 1 and 5.…”

Section: Resultsmentioning

confidence: 99%

“…In connection with our research on the synthesis of functionalized lactams through transition-metal-catalyzed reactions [5], we have launched a program directed toward the total synthesis of salinosporamide A. Our plan is based on the transition-metal-catalyzed hydroamidation of alkynes.…”

Section: Introductionmentioning

confidence: 99%

Synthetic studies of salinosporamide A through the intramolecular hydroamidation of alkynes

Kamisaki

Kobayashi

Kimachi

et al. 2011

Journal of Organometallic Chemistry

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a b s t r a c tRhodium-catalyzed intramolecular hydroamidation of alkynes was carried out to construct the synthetic intermediates of a proteasome inhibitor, salinosporamide A. Several alkynyl formamides were synthesized and subjected to the hydroamidation reaction. Some derivatives with a methoxymethyl (MOM) or 2-methoxy-2-propyl (MOP) group near the reaction site were converted to the corresponding lactams in excellent yields.

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“…88 The reaction proceeded exclusively in a 5exo mode, giving the corresponding (Z)-alkenes as major products. A novel method for the synthesis of five-to seven-membered α-alkylidene lactams by the palladium-catalysed intramolecular cyanoamidation of alkynyl and alkenyl cyanoformamides has been developed.…”

Section: Rearrangement Involving Organometallic Compoundsmentioning

confidence: 99%

Molecular Rearrangements: Part 2. Other Reactions

Brandi

Gensini

2010

Organic Reaction Mechanisms · 2006

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The formation of α-phenyl-β-halovinyl cation, β-phenyl-α-halovinyl cation, and also the halogen-bridged and the spirocyclic phenyl-bridged cations, as intermediates of protonation of phenylethynyl halides, or of halogen addition to phenylethynes, has been evaluated by DFT at the B3LYP/6-31+G(d) level and, for comparison in representative cases, by B3LYP/6-311++G(d,p). 1 Structural and mechanistic studies of the lithium diisopropylamide (LDA)-mediated anionic Fries rearrangements of aryl carbamates have been described. 2 Substituents at the meta position of the arene (H, OMe, F) and the dialkylamino moiety of the carbamate (Me 2 N, Et 2 N, and i-Pr 2 N) markedly influence the relative rates of ortholithiation and subsequent Fries rearrangement. The mechanism of the Fries rearrangement of aryl formates promoted by boron trichloride has been studied by means of 1 H, 2 H, and 11 B NMR spectroscopy and DFT calculations. 3 After the formation of a 1:1 substrate -Lewis acid adduct, the rearrangement proceeds in two steps, beginning with the cleavage of the ester bond and the release of formyl chloride in situ, which, in turn, acts as a formylating agent, introducing 451

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Palladium-Catalyzed Intramolecular Cyanoamidation of Alkynyl and Alkenyl Cyanoformamides

Cited by 131 publications

References 18 publications

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

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

Synthetic studies of salinosporamide A through the intramolecular hydroamidation of alkynes

Molecular Rearrangements: Part 2. Other Reactions

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