The regio- and stereoselective synthesis and subsequent Hiyama cross coupling of pentafluorophenyldimethylvinylsilanes has been developed, thus providing a convenient and robust method for the diversity-oriented synthesis of (E)-, (Z)- and alpha-disubstituted alkenes from terminal alkynes. Pentafluorophenyldimethylvinylsilanes undergo cross-coupling reactions with excellent selectivity and in good yields, offering an attractive alternative to existing masked silanols.

Herein, a new copper-catalysed strategy for the synthesis of rare nitrogen-linked seven-, eight- and nine-membered biaryl ring systems is described. It is proposed that the reaction proceeds through a highly activated intramolecularly co-ordinated copper catalyst. The process is technically simple, proceeds under relatively mild conditions, displays a broad substrate scope and forms biologically valuable products that are difficult to synthesise by other methods. We envisage that this methodology will prove useful in a wide synthetic context, with possible applications in both target-oriented and diversity-oriented synthesis.

A wide range of organozinc substrates may be oxidized in the presence of catalytic copper to give carbon-carbon bonds in high yield.

Copper-Catalyzed Oxidation of Organozinc Halides. -A variety of organozinc compounds is oxidized with a dinitroaryl piperazinyl ketone in the presence of copper(I) resulting in carbon-carbon bond formation. The new methodology is compatible with various functional groups and can be applied to the total synthesis of the alkaloid buflavine (VIII). -(SU, X.; FOX, D. J.; BLACKWELL, D. T.; TANAKA, K.; SPRING*, D. R.; Chem. Commun. (Cambridge) 2006, 37, 3883-3885; Dep. Chem., Univ. Cambridge, Cambridge CB2 1EW, UK; Eng.) -R. Staver 06-055

A strategy is described for the stereoselective synthesis of substituted (E)-, (Z)-, and a-disubstituted butadienes from terminal alkynes by the copper-mediated coupling of geometrically-defined alkenyl silanes. Proof-of-concept results that demonstrate the feasibility of this approach are presented.Conjugated polyene systems are a commonly encountered structural feature in natural products 1 and some optical materials; 2 consequently the development of methods to access such bonding arrangements in a stereoselective fashion has attracted interest amongst synthetic chemists. 3 Herein we outline a strategy for the regio-and stereoselective synthesis of (E)-, (Z)-, and a-disubstituted butadienes from a common terminal alkyne precursor. Such chemistries could offer an efficient means of rapidly achieving structural diversification from a common starting material; as such, they could also be exploited in reagent-based diversity-oriented synthesis (DOS) pathways. 4,5 In line with our group's continued interest in copperbased methods for carbon-carbon bond construction 6 we were interested in exploring the thermolytic dimerisation of geometrically-defined alkenylcopper species as a route towards the desired E-, Z-, and a-substituted butadiene architectures (1-3, Scheme 1). It was envisaged that such copper species could be accessed by transmetalation from suitable geometrically-defined alkenylmetal precursors (or latent functional equivalents), which could ideally be selectively generated from a common alkyne starting material. We were interested in examining the use of alkenylsilanes (of the general form 4-6) in this context: there are a number of reactions that seemingly involve silicon-copper transmetalations, 7 and a range of catalytic methods have been developed for the stereoselective hydrosilylation of (terminal) alkynes, allowing the formation of E-, Z-, and a-isomers in a controllable fashion. 8 Thus if an alkenyl silane moiety capable of undergoing stereospecific transmetalation to copper could be identified, it may be possible to effect the stereoselective formation of geometrically-defined alkenylsilanes 4-6 containing this moiety (by hydrosilylation using the parent silane 7, Scheme 1) and convert these into the corresponding alkenylcopper species for subsequent coupling. Overall, it was envisaged that this sequence could provide access to all possible E-, Z-, and a-disubstituted butadiene isomers 1-3 from a common terminal alkyne precursor 8. In this letter we present proof-of-concept results that demonstrate the feasibility of this approach.Our synthetic strategy was dependent upon the identification of (E)-, (Z)-, and a-alkenylsilane precursors that could be readily prepared with geometrical control and undergo stereospecific transmetalation to copper under mild conditions. Ideally, all desired geometrical isomers of such alkenylsilanes could be generated by hydrosilylation from the same starting material through variation in the catalyst employed. Yoshida et al. have reported that Scheme 1 Outline of o...