101
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Campaña AG, Fuentes N, Gómez-Bengoa E, Mateo C, Oltra JE, Echavarren AM, Cuerva JM. Sodium Tetramethoxyborate: An Efficient Catalyst for Michael Additions of Stabilized Carbon Nucleophiles. J Org Chem 2007; 72:8127-30. [PMID: 17880141 DOI: 10.1021/jo701354c] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Sodium tetramethoxyborate, easily prepared by reaction of inexpensive sodium borohydride with methanol, possesses a suitable combination of a Lewis base and a Lewis acid to catalyze Michael reactions at room temperature under practically neutral conditions. This reaction provides good to excellent yields of Michael addition products from a broad scope of Michael donor and Michael acceptor reagents.
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102
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Campaña AG, Estévez RE, Fuentes N, Robles R, Cuerva JM, Buñuel E, Cárdenas D, Oltra JE. Unprecedented Hydrogen Transfer from Water to Alkenes and Alkynes Mediated by TiIII and Late Transition Metals. Org Lett 2007; 9:2195-8. [PMID: 17480090 DOI: 10.1021/ol070779i] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We describe how alkenes and alkynes can be hydrogenated under mild conditions by hydrogen transfer from water mediated by titanocene(III) and a substoichiometric quantity of one of the late transition metals usually employed as hydrogenation catalysts. This process proceeds presumably by H-atom transfer from TiIII-coordinated water to the late transition metal partner (depicted in the drawing above), a mechanism in support of which we provide theoretical and experimental evidence.
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103
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Estévez RE, Oller-López JL, Robles R, Melgarejo CR, Gansäuer A, Cuerva JM, Oltra JE. Stereocontrolled Coupling between Aldehydes and Conjugated Alkenals Mediated by TiIII/H2O. Org Lett 2006; 8:5433-6. [PMID: 17107040 DOI: 10.1021/ol0620390] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the presence of water, titanocene(III) complexes promote a stereoselective C-C bond-forming reaction that provides gamma-lactols by radical coupling between aldehydes and conjugated alkenals. The method is useful for both intermolecular reactions and cyclizations. The relative stereochemistry of the products can be predicted with confidence with the aid of model Ti-coordinated intermediates. The procedure can be carried out enantioselectively using chiral titanocene catalysts. [reaction: see text].
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104
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Cuerva JM, Campaña AG, Justicia J, Rosales A, Oller-López JL, Robles R, Cárdenas DJ, Buñuel E, Oltra JE. Water: The Ideal Hydrogen-Atom Source in Free-Radical Chemistry Mediated by TiIII and Other Single-Electron-Transfer Metals? Angew Chem Int Ed Engl 2006. [DOI: 10.1002/ange.200600831] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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105
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Cuerva JM, Campaña AG, Justicia J, Rosales A, Oller-López JL, Robles R, Cárdenas DJ, Buñuel E, Oltra JE. Water: The Ideal Hydrogen-Atom Source in Free-Radical Chemistry Mediated by TiIII and Other Single-Electron-Transfer Metals? Angew Chem Int Ed Engl 2006; 45:5522-6. [PMID: 16850518 DOI: 10.1002/anie.200600831] [Citation(s) in RCA: 158] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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106
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Rosales A, Estévez RE, Cuerva JM, Oltra JE. Enantiospecific strategy towards oxygen-bridged terpenoids: tandem transannular-cyclization and ring-contraction processes. Angew Chem Int Ed Engl 2006; 44:319-22. [PMID: 15614888 DOI: 10.1002/anie.200461210] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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107
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Bazdi B, Oller-López JL, Cuerva JM, Oltra JE, Mansour AI. Composition of the Essential Oil from the Seeds ofAbies marocana. JOURNAL OF ESSENTIAL OIL RESEARCH 2006. [DOI: 10.1080/10412905.2006.9699053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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108
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Justicia J, Oltra JE, Cuerva JM. Exploiting PdII and TiIII Chemistry To Obtain γ-Dioxygenated Terpenoids: Synthesis of Rostratone and Novel Approaches to Aphidicolin and Pyripyropene A. J Org Chem 2006. [DOI: 10.1021/jo060116z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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109
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Justicia J, Oller-López JL, Campaña AG, Oltra JE, Cuerva JM, Buñuel E, Cárdenas DJ. 7-endo radical cyclizations catalyzed by titanocene(III). Straightforward synthesis of terpenoids with seven-membered carbocycles. J Am Chem Soc 2006; 127:14911-21. [PMID: 16231947 DOI: 10.1021/ja054316o] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We describe a novel procedure for the straightforward synthesis of seven-membered carbocycles via free-radical chemistry, based on titanocene(III)-catalyzed 7-endo-dig and 7-endo-trig cyclizations. This procedure has proved to be useful for the chemical preparation of terpenoids with different skeletons containing cycloheptane rings, including the first total syntheses of dauca-4(11),8-diene (2), barekoxide (3), authentic laukarlaol (81), and a valparane diterpenoid (72), as well as a substantially improved synthesis of karahanaenone (1). We also provide theoretical and experimental evidence in support of a plausible mechanism, which may rationalize the preference for the unusual 7-endo cyclization mode shown by radicals with substitution patterns characteristic of the linalyl, nerolidyl, and geranyl linalyl systems. In light of these chemical findings, we discuss the potential involvement of radical cyclizations in the biosynthesis of some terpenoids containing seven-membered carbocycles.
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110
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Oller-López JL, Rodríguez R, Cuerva JM, Oltra JE, Bazdi B, Dahdouh A, Lamarti A, Mansour AI. Composition of the Essential Oils ofCistus ladaniferusandC. monspeliensisfrom Morocco. JOURNAL OF ESSENTIAL OIL RESEARCH 2005. [DOI: 10.1080/10412905.2005.9698992] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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111
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Justicia J, Oltra JE, Cuerva JM. Exploiting PdII and TiIII Chemistry To Obtain γ-Dioxygenated Terpenoids: Synthesis of Rostratone and Novel Approaches to Aphidicolin and Pyripyropene A. J Org Chem 2005; 70:8265-72. [PMID: 16209566 DOI: 10.1021/jo0502910] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In nature there are several terpenoids with a characteristic gamma-dioxygenated system on the A ring, and many of them show interesting pharmacological properties. We have developed a novel strategy for the synthesis of these terpenoids involving three stages: (a) the selective epoxidation of commercial polyenes, (b) titanium(III)-catalyzed cyclization of the epoxypolyprenes thus obtained, and (c) Pd-mediated remote functionalization of the equatorial methyl group attached at C-4 on ring A of the cyclic terpenoid thus formed. This strategy has proved to be useful for the synthesis of the natural labdane rostratone (1) and related terpenoids, as well as for advanced synthetic approaches toward the pharmacologically active products aphidicolin (2) and pyripyropene A (3).
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112
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Oller-López JL, Iranzo M, Mormeneo S, Oliver E, Cuerva JM, Oltra JE. Bassianolone: an antimicrobial precursor of cephalosporolides E and F from the entomoparasitic fungus Beauveria bassiana. Org Biomol Chem 2005; 3:1172-3. [PMID: 15785802 DOI: 10.1039/b417534d] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have established the chemical structure of (+)-bassianolone (3), the antimicrobial compound precursor of cephalosporolides E and F, and that of the furan metabolite 4 from the entomopathogenic fungus Beauveria bassiana.
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113
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Justicia J, Oltra JE, Barrero AF, Guadaño A, González-Coloma A, Cuerva JM. Total Synthesis of 3-Hydroxydrimanes Mediated by Titanocene(III) - Evaluation of Their Antifeedant Activity. European J Org Chem 2005. [DOI: 10.1002/ejoc.200400634] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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114
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Rosales A, Estévez RE, Cuerva JM, Oltra JE. Enantiospecific Strategy Towards Oxygen-Bridged Terpenoids: Tandem Transannular-Cyclization and Ring-Contraction Processes. Angew Chem Int Ed Engl 2004. [DOI: 10.1002/ange.200461210] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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115
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Justicia J, Oltra JE, Cuerva JM. General Approach to Polycyclic Meroterpenoids Based on Stille Couplings and Titanocene Catalysis. J Org Chem 2004; 69:5803-6. [PMID: 15307765 DOI: 10.1021/jo049253r] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We describe a novel convergent procedure that has proved useful in the synthesis of a wide range of meroterpenoid-related structures containing a mono-, sesqui-, or diterpenoid moiety linked to a nonfused aromatic subunit with various substitution patterns. The key steps were the Stille-type coupling of aryl stannanes and allylic carbonates, followed by the titanocene-catalyzed domino cyclization of aryl epoxypolyprenes. The coupling reaction was perfectly compatible with preformed epoxides, while the sequential cyclization, which presumably proceeded via alkyl radicals inert to benzene derivatives, selectively provided exocyclic alkenes.
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116
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Justicia J, Oltra J, Cuerva JM. Palladium mediated C–H activation in the field of terpenoids: synthesis of rostratone. Tetrahedron Lett 2004. [DOI: 10.1016/j.tetlet.2004.04.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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117
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Justicia J, Rosales A, Buñuel E, Oller-López JL, Valdivia M, Haïdour A, Oltra JE, Barrero AF, Cárdenas DJ, Cuerva JM. Titanocene-Catalyzed Cascade Cyclization of Epoxypolyprenes: Straightforward Synthesis of Terpenoids by Free-Radical Chemistry. Chemistry 2004; 10:1778-88. [PMID: 15054765 DOI: 10.1002/chem.200305647] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The titanocene-catalyzed cascade cyclization of epoxypolyenes, which are easily prepared from commercially available polyprenoids, has proven to be a useful procedure for the synthesis of C(10), C(15), C(20), and C(30) terpenoids, including monocyclic, bicyclic, and tricyclic natural products. Both theoretical and experimental evidence suggests that this cyclization takes place in a nonconcerted fashion via discrete carbon-centered radicals. Nevertheless, the termination step of the process seems to be subjected to a kind of water-dependent control, which is unusual in free-radical chemistry. The catalytic cycle is based on the use of the novel combination Me(3)SiCl/2,4,6-collidine to regenerate the titanocene catalyst. In practice this procedure has several advantages: it takes place at room temperature under mild conditions compatible with different functional groups, uses inexpensive reagents, and its end step can easily be controlled to give exocyclic double bonds by simply excluding water from the medium.
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118
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Rosales A, Oller-López JL, Justicia J, Gansäuer A, Oltra JE, Cuerva JM. Unprecedented Barbier-type reactions catalysed by titanocene(iii). Chem Commun (Camb) 2004:2628-9. [PMID: 15543313 DOI: 10.1039/b411173g] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Selective Barbier-type allylations, benzylations and propargylations of aldehydes and ketones can be carried out under extremely mild conditions employing titanocene(III) complexes as catalysts. In this way, chiral titanocene catalysts provided yields ranging from 50-80% of optically active products.
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119
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Barrero AF, Rosales A, Cuerva JM, Oltra JE. Unified synthesis of eudesmanolides, combining biomimetic strategies with homogeneous catalysis and free-radical chemistry. Org Lett 2003; 5:1935-8. [PMID: 12762690 DOI: 10.1021/ol034510k] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[reaction: see text] A general procedure for the synthesis of both 12,6- and 12,8-eudesmanolides has been developed. The key step is the titanocene-catalyzed radical cyclization of accessible epoxygermacrolides. The novel reagent 2,4,6-trimethyl-1-trimethylsilylpyridinium chloride, both compatible with oxiranes and capable of regenerating Cp(2)TiCl(2) from Cp(2)Ti(Cl)H and Cp(2)Ti(Cl)OAc, played an important role in the catalytic cycle leading to exocyclic alkenes.
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120
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Barrero AF, Rosales A, Cuerva JM, Gansäuer A, Oltra J. Titanocene-catalysed, selective reduction of ketones in aqueous media. A safe, mild, inexpensive procedure for the synthesis of secondary alcohols via radical chemistry. Tetrahedron Lett 2003. [DOI: 10.1016/s0040-4039(02)02703-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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121
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Méndez M, Cuerva JM, Gómez-Bengoa E, Cárdenas DJ, Echavarren AM. Intramolecular coupling of allyl carboxylates with allyl stannanes and allyl silanes: a new type of reductive elimination reaction? Chemistry 2002; 8:3620-8. [PMID: 12203288 DOI: 10.1002/1521-3765(20020816)8:16<3620::aid-chem3620>3.0.co;2-p] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The palladium-catalyzed intramolecular coupling of allyl stannanes with allyl carboxylates provides a general synthesis of five- and six-membered-ring carbocycles. The intramolecular coupling leads selectively to trans five-membered carbocycles and cis six-membered carbocycles, regardless of the cis or trans configuration of the allylic functions in the starting material. For example, the stereoselective synthesis of 10-epi-elemol demonstrated the cis configuration of the six-membered carbocycles. The related Oppolzer cyclization leads to lower yields, or fails completely, with substrates substituted at C-3 of the allyl and/or alkene terminus. The palladium-catalyzed intramolecular coupling of allyl silanes with allyl trifluoroacetates allows the synthesis of trans five-membered-ring carbocycles and requires the use of a bicyclic phosphite as the ligand. DFT calculations suggest that the preferred pathway for the intramolecular allyl/allyl coupling is by formation of the Cbond;C bond between the C-3 termini of the allyl ligands of bis(eta(3)-allyl)palladium complexes.
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122
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Cuerva JM, Cárdenas DJ, Echavarren AM. Intramolecular Michael-type addition of azadienes to 1,4-naphthoquinones instead of Aza-Diels–Alder cycloaddition: a synthesis of ascididemin. ACTA ACUST UNITED AC 2002. [DOI: 10.1039/b202555h] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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123
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Echavarren AM, Perez M, Castano AM, Cuerva JM. Palladium-Catalyzed Reductive Coupling of Acid Chlorides with .beta.-Stannyl Enones: Synthesis of 1,4-Diketones and Mechanistic Aspects. J Org Chem 2002. [DOI: 10.1021/jo00094a032] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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124
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Barrero AF, Oltra JE, Cuerva JM, Rosales A. Effects of solvents and water in Ti(III)-mediated radical cyclizations of epoxygermacrolides. Straightforward synthesis and absolute stereochemistry of (+)-3alpha-hydroxyreynosin and related eudesmanolides. J Org Chem 2002; 67:2566-71. [PMID: 11950302 DOI: 10.1021/jo016277e] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The Cp(2)TiCl-mediated rearrangement of 1,10-epoxy-11beta,13-dihydrocostunolide (4) was carried out using different solvents and additives to develop an expeditious procedure for the synthesis of natural eudesmanolides via free-radical chemistry. In the nonhalogenated solvents THF, benzene, and toluene the transannular cyclization, initiated by the homolytic opening of the oxirane ring, selectively led to the desired exocyclic alkene 5. When water was added to THF, however, the main product was reduced eudesmanolide 8. Experiments with D(2)O confirmed that the H-4 of 8 comes from water. To rationalize these results, a mechanistic hypothesis based on a water-solvated Cp(2)TiCl complex is proposed. Finally, the usefulness of Cp(2)TiCl for the synthesis of natural eudesmanolides has been proved using this reagent in the key step for the chemical preparation of (+)-3alpha-hydroxyreynosin (1) and (+)-reynosin (17). These syntheses confirmed the chemical structure of 1 and established the absolute stereochemistry of the natural products 1 and 17. The results obtained suggest that the combination of the biomimetic strategy employed, with Ti(III)-mediated free-radical chemistry, may come to represent a general method for the enantiospecific synthesis of more than 170 natural eudesmanolides containing an exocyclic double bond between C-4 and C-15.
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125
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Barrero AF, Cuerva JM, Alvarez-Manzaneda E, Oltra J, Chahboun R. First synthesis of achilleol A using titanium(III) chemistry. Tetrahedron Lett 2002. [DOI: 10.1016/s0040-4039(02)00358-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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