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Volumn 70, Issue 17, 2005, Pages 6848-6862

Regiocontrolled, palladium-catalyzed bisfunctionalization of allenyl esters. Multicomponent coupling approaches to highly substituted α,β-unsaturated δ-lactones

Author keywords

[No Author keywords available]

Indexed keywords

ALDEHYDES; CATALYSIS; CATALYSTS; INORGANIC ACIDS; MOLECULAR STRUCTURE; PALLADIUM; REACTION KINETICS;

EID: 23644461773     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo050886v     Document Type: Article
Times cited : (63)

References (140)
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    • For a general discussion of the reactivity of bis-π-allylpalladium complexes, including computational studies, see: (a) Wallner, O. O.; Szabó, K. J. Chem. Eur. J. 2003, 9, 4025-4030.
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    • For applications of the bis-π-allylpalladium 7 complexes as catalytic intermediates in synthetically useful processes, see: (d) Wallner, O. A.; Szabó;, K. J. J. Org. Chem. 2003, 68, 2934-2943.
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    • note
    • 3-mode. Selectivity for the electrophilic attack on the more electron-rich and the less substituted allyl ligands has been demonstrated experimentally; see refs 10a,b,g,k.
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    • note
    • σ-π* hyperconjugative interaction was responsible for the nucleophilic reactivity of the terminal and often substituted vinylic carbon, rationalizing the regioselective formation of branched organic products. See references 10a,b.
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    • For methods utilizing the reactivity of allylic Reformatsky reagents or their stannyl analogues, see: (f) Brenna, E.; Fuganti, C.; Ronzani, S.; Serra, S. Can. J. Chem. 2002, 80, 714-723.
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    • For studies on the structure and reactivity of stoichiometric bis-π-allylpalladium complexes, see: (a) Storzer, U.; Walter, O.; Zevaco, T.; Dinjus, E. Organometallics 2005, 24, 514-520.
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    • note
    • 1H NMR spectrum recorded on crude reaction mixtures indicated the presence of multiple byproducts that could not be characterized.
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    • note
    • 1H NMR spectrum recorded on the crude reaction mixture did not reveal the presence of significant quantities of byproducts.
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    • note
    • 1H NMR NOE experiment on alcohol 5 revealed that irradiation of the signal for the vinylic proton at δ 6.23 (s) led to the NOE enhancement of the signal at δ 7.46 (dd) corresponding to a proton in the p-methoxyphenyl substituent, as expected for the assigned structure of alcohol 5 with the (E) double bond geometry.
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    • note
    • Isolated alcohol 5 (1.0 equiv) was treated with boronic acid 2a (2.0 equiv), catalyst 1a (10 mol % Pd), and CsF (4.0 equiv) under the reaction conditions (THF, rt) in the absence of the aldehyde and allene components for 2 days to afford 45% yield of lactone 6a.
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    • In comparison to the aliphatic allene (1,2-nonadiene) used in our prior work, the allenyl ester 3a would be expected to operate as a stronger ligand for palladium(II) complexes. For the discussion of binding of olefins to palladium complexes, see: Hartley, F. R. Chem. Rev. 1969, 69, 799-844.
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    • A structure of one possible regioisomer of the oxidative cyclization product is shown below (additional ligands on palladium were omitted for clarity). Oxidative homocoupling of allenes mediated by Pt(0) complexes providing corresponding Pt(II) metalacycles is known; see: (a) Stephan, C.; Munz, C.; Dieck, T. J. Organomet. Chem. 1994, 468, 273-278.
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    • note
    • 1H NMR spectra, the trans geometry of the olefin in lactone 6e was confirmed by X-ray crystallographic analysis.
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    • note
    • Thus, the presented methodology provides an opportunity for further elaboration and diversification of the lactones via a subsequent palladium(0)-catalyzed cross-coupling or a Heck-type protocol initiated by an in situ addition of palladium(0) catalyst and suitable reagents. See ref 1a.
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    • note
    • 1H NMR NOE experiments on the inseparable mixture of alcohol 8 and lactone 60 revealed that irradiation of the signal for the vinylic proton in alcohol 8 at δ 6.33 (s) led to the NOE enhancement of the signal at δ 6.84 (d) corresponding to the H-3 proton in the 5-bromo-2-indolyl substituent. Furthermore, irradiation of the H-3 proton in the indolyl ring at δ 6.84 led to the NOE enhancement of the signals at δ 6.33 (s) and at δ 7.75 (d), corresponding to the vinylic proton, and a proton in the aromatic ring of the indolyl substituent, respectively, as expected for the assigned structure of alcohol 8 with the (E) double bond geometry.
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    • note
    • In this protocol, racemic allenes 3c and 3d were employed, and no attempts were made to investigate whether a single enantiomer of each allenyl ester may have reacted preferentially in the coupling catalyzed by a nonracemic palladium(II) complex 1a.
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    • note
    • 2) with boronic acid 2a and benzaldehyde 4a under the standard coupling conditions (Scheme 1, no lactonization) did not afford the desired alcohols, and unreacted substrates along with small quantities (<10%) of olefinic byproducts arising from coupling of the allenes and the boronic acid were isolated. Under the same conditions, 3,4-pentadiene-2-one (X = C(O)Me) and 2,3-butadienenitrile (X = CN) afforded rather complex reaction mixtures containing several products of the three-component coupling. The alcohol shown below could be isolated in 22% yield.
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    • For selected reactions catalyzed by diverse transition metal complexes, which involve transmetalation from boronic acids to transition metals as the event that initiates the catalytic cycle, see: (b) Andeppan, M. M. S.; Nilsson, P.; Larhed, M. Chem. Commun. 2004, 218-219.
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    • note
    • 3 in EtOH gave rise to small quantities of the corresponding olefinic byproduct of type 7, suggesting that modifications to the lactonization procedure might be warranted, depending on the electronic properties of the boronic acids and aldehydes used. Alternative pathways providing the olefinic byproducts via palladium(0)- mediated steps appear unlikely, since precipitation of palladium(0) was not observed and the reaction remained catalytic in palladium.
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    • For a discussion of the different bonding modes available to palladium enolates, see: (a) Tian, G.; Boyle, P. D.; Novak, B. M. Organometallics 2002, 21, 1462-1465.
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    • note
    • Treatment of arylstannane (p-methoxyphenyl(trimethyl)tin, 1.2 equiv) with benzaldehyde 4a (1.0 equiv), ethyl 2,3-butadienoate 3a (5.0 equiv), and with catalyst 1a (10 mol % Pd) in THF (60 deg;C, 24 h) followed by the standard (Table 1) lactonization conditions afforded lactone 6a in 59% yield, and no regioisomeric products were detected in the crude reaction mixture. The elevated temperature was required to ensure an efficient transmetalation. In a control experiment reported in an earlier communication (ref 13), the addition of allyltributyltin to benzaldehyde at 60 °C failed to afford any homoallylic alcohol products. For a discussion of the mechanism of Pd(II)-catalyzed reactions of allylstannanes with aldehydes proposing the involvement of bis-π-allylpalladium complexes, see ref 10k.
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    • Allylboronic acids and allylboranes undergo facile uncatalyzed reactions with aldehydes; see: (a) Brown, H. C.; Racherla, Y. S.; Pellechia, P. J. J. Org. Chem. 1990, 55, 1866-1874.
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    • The presence of a Lewis acid catalyst is required to enable the reactions between allylstannanes and aldehydes, see: (c) Maruayama, K.; Ishihara, Y.; Yamamoto, Y. Tetrahedron Lett. 1981, 22, 4235-4238.
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    • note
    • Proposed "open" transition states for the allyl transfer from O-bonded allylpalladium(II) ester enolates IIIC (Figure 4) are shown below. The steric bulk of substituent R at the terminal vinylic carbon may control the preference for formation of either (E) (R = H) or (Z) (R = Me, n-hexyl) alcohols.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.