[show abstract][hide abstract] ABSTRACT: This review highlights the recent applications of titanocene(III) complexes in the field of natural product synthesis from the seminal precedents to the development of modern catalytic methods. The power of the titanocene(III)-based approaches is demonstrated by the straightforward syntheses of many natural products from readily available starting materials.
[show abstract][hide abstract] ABSTRACT: In this work we show that the unique combination of a nickel catalyst and Cp2TiCl allows the direct conjugate addition of aryl and alkenyl iodides, bromides and, in less extension, chlorides and triflates to alpha,beta-unsaturated carbonyls at room temperature, without requiring the previous formation of an organometallic nucleophile. The reaction proceeds inter- and intramolecularly with good functional-group compatibility, which is key for the development of free protecting group methodologies. Carbo- and heterocycles of five and six-membered rings are obtained in good yields. Moreover, some insights about the mechanism involved have been obtained from cyclic voltammetry, UV-Vis and HRTEM measurements.
The Journal of Organic Chemistry 01/2014; · 4.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: Extended reach: A calculated mechanism for long-range proton-coupled electron transfer (PCET, see picture) through an array of structured water molecules between Fe(III) -Fe(III) complexes accounts for the reaction enthalpy and kinetic isotope effect previously measured for this reaction. This mechanism may be general and occur for other hydroxo-metal complexes.
[show abstract][hide abstract] ABSTRACT: A versatile Ti/Ni multimetallic protocol is described for the efficient catalysis of two different reactions, namely a Heck- and reductive-type cyclization of alkyl iodides, in the absence or presence of water, respectively. Noteworthy, the versatility of Ti(III) chemistry allows an oxidative ending step under reductive conditions to give Heck-type products, and the good H-atom transfer capabilities of Ti(III)-aqua complexes ensure reductive-type cyclizations.
[show abstract][hide abstract] ABSTRACT: This tutorial review highlights the development of radical-based bioinspired synthesis of terpenes from the initial proposal to the development of modern catalytic methods for performing such processes. The power of the radical approach is demonstrated by the straightforward syntheses of many natural products from readily available starting materials. The efficiency of these processes nicely complements the described cationic polyolefin cyclisations and even suggests that modern radical methods provide means to improve upon nature's synthetic pathways.
Chemical Society Reviews 07/2011; 40(7):3525-37. · 24.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: The allylation, crotylation and prenylation of aldehydes and ketones with stable and easily handled allylic carbonates is promoted by a Ti/Pd catalytic system. This Ti/Pd bimetallic system is especially convenient for the allylation of ketones, which are infrequent substrates in other related protocols, and can be carried out intramolecularly to yield five- and six-membered cyclic products with good stereoselectivities. In addition, Ti/Pd-mediated reductions and Würtz-type dimerisation reactions can be readily carried out from allyl carbonates and carboxylates.
[show abstract][hide abstract] ABSTRACT: The H-atom transfer (HAT) from water to ketyl radicals, mediated by titanocene(iii) aqua-complexes, can explain the Ti(III)-promoted reduction of ketones in aqueous medium better than the conventional House mechanism. Moreover, we also report novel evidences supporting the existence of these titanocene(iii) aqua-complexes.
[show abstract][hide abstract] ABSTRACT: Theoretical and experimental studies on the gold(I)-catalyzed formal [4+2] cycloaddition of dienynes are consistent with a mechanism that proceeds by means of cyclopropyl gold(I) carbenes instead of simple carbocations. This work shows that homoallylic stabilization is significant even for systems in which the tertiary carbocation is stabilized by two methyl groups.
Chemistry - An Asian Journal 10/2010; 6(2):482-6. · 4.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: In recent years solid evidence of HAT reactions involving water as hydrogen atom source have been presented. In this work we demonstrate that the efficiency of titanocene(III) aqua complexes as an unique class of HAT reagents is based on two key features: (a) excellent binding capabilities of water toward titanocene(III) complexes and (b) a low activation energy for the HAT step. The theory has predictive capabilities fitting well with the experimental results and may aid to find more examples of this remarkable radical reaction.
Journal of the American Chemical Society 09/2010; 132(36):12748-56. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: Titanocene(III) chemistry has emerged in the last decades as an indispensable tool in C-C bond-forming reactions. In this context, pinacol and related reactions allow the stereoselective synthesis of vicinal diols. In this work, we present new applications of these reactions using as starting materials aromatic ketones. Simple and smooth reaction conditions have been developed and have been applied for inter- and intramolecular processes. We also describe that although Cp(2)TiCl is usually used as a monoelectronic reducing agent, it can be also used as an efficient Lewis acid.
The Journal of Organic Chemistry 04/2009; 74(9):3616-9. · 4.56 Impact Factor
[show abstract][hide abstract] 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.
The Journal of Organic Chemistry 11/2007; 72(21):8127-30. · 4.56 Impact Factor
[show abstract][hide abstract] 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.