Addition of alkenes and alkynes

Selective addition of alkenes and alkynes to aromatic compounds has also been performed by ruthenium-catalyzed aromatic C-H bond activation. Carbon-carbon bond formation occurs at the ortho positions of aromatic compounds, assisted by the neighboring functional group chelation. The reaction, catalyzed by RuH2(CO)(PPh3)3, was efficient with aromatic and heteroaromatic compounds, with various functional groups, and a variety of alkenes and alkynes [ 121 ] (Eq. 90). Activation of vinylic C-H bonds can occur in a similar manner. 

A detailed account of the (2 + 2)-photocycloaddition reactions of homo-quinones has been published. The addition reactions afford regio and exo.endo isomers of tricyclic diones. The major product is thought to arise from the more stable triplet 1,4-biradical intermediate.A review has reported on the addition of alkenes and alkynes to the enone system of homobenzoquinones. Dibromo-9-(3-oxo-3-phenylprop-l-ynyl)-[9 -fluoren-9-yl-3-fluoren-9-ylidene-1-phenylpropenone is photochromic in the crystalline state. 

Still, I. W. J., Kwan, M.-H., and Palmer, G. E., Photo-addition of alkenes and alkynes to 3-carene-... 

Addition of Alkenes and/or Alkynes to Alkenes and/or Alkynes Hydro-alkenyl-addition... 

For a summary and detailed discussion of the stereochemistry of electrophilic additions to alkenes and alkynes see R. C. Fahey, in Topics in Stereochemistry, Vol. 3,... 

Iron porphyrins containing vinyl ligands have also been prepared by hydromet-allation of alkynes with Fe(TPP)CI and NaBH4 in toluene/methanol. Reactions with hex-2-yne and hex-3-yne are shown in Scheme 4. with the former giving two isomers. Insertion of an alkyne into an Fe(III) hydride intermediate, Fe(TPP)H, formed from Fe(TPP)Cl with NaBH4, has been proposed for these reactions. " In superficially similar chemistry, Fe(TPP)CI (present in 10 mol%) catalyzes the reduction of alkenes and alkynes with 200 mol% NaBH4 in anaerobic benzene/ethanol. For example, styrene is reduced to 2,3-diphenylbutane and ethylbenzene. Addition of a radical trap decreases the yield of the coupled product, 2,3-diphenylbutane. Both Fe(lll) and Fe(II) alkyls, Fe(TPP)CH(Me)Ph and [Fe(TPP)CH(Me)Ph] , were propo.sed as intermediates, but were not observed directly. ... 

Until recently, iron-catalyzed hydrogenation reactions of alkenes and alkynes required high pressure of hydrogen (250-300 atm) and high temperature (around 200°C) [21-23], which were unacceptable for industrial processes [24, 25]. In addition, these reactions showed low or no chemoselectivity presumably due to the harsh reaction conditions. Therefore, modifications of the iron catalysts were desired. 

The hydrosi(ly)lations of alkenes and alkynes are very important catalytic processes for the synthesis of alkyl- and alkenyl-silanes, respectively, which can be further transformed into aldehydes, ketones or alcohols by estabhshed stoichiometric organic transformations, or used as nucleophiles in cross-coupling reactions. Hydrosilylation is also used for the derivatisation of Si containing polymers. The drawbacks of the most widespread hydrosilylation catalysts [the Speier s system, H PtCl/PrOH, and Karstedt s complex [Pt2(divinyl-disiloxane)3] include the formation of side-products, in addition to the desired anh-Markovnikov Si-H addition product. In the hydrosilylation of alkynes, formation of di-silanes (by competing further reaction of the product alkenyl-silane) and of geometrical isomers (a-isomer from the Markovnikov addition and Z-p and -P from the anh-Markovnikov addition. Scheme 2.6) are also possible. 

The metal catalysed hydroboration and diboration of alkenes and alkynes (addition of H-B and B-B bonds, respectively) gives rise to alkyl- or alkenyl-boronate or diboronate esters, which are important intermediates for further catalytic transformations, or can be converted to useful organic compounds by established stoichiometric methodologies. The iyn-diboration of alkynes catalysed by Pt phosphine complexes is well-established [58]. However, in alkene diborations, challenging problems of chemo- and stereo-selectivity control stiU need to be solved, with the most successful current systems being based on Pt, Rh and An complexes [59-61]. There have been some recent advances in the area by using NHC complexes of Ir, Pd, Pt, Cu, Ag and Au as catalysts under mild conditions, which present important advantages in terms of activity and selectivity over the established catalysts. 

Organometallic complexes of the /-elements have been reported that will perform both intra-and intermolecular hydroamination reactions of alkenes and alkynes, although these lie outside of the scope of this review.149-155 Early transition metal catalysts are not very common, although a number of organometallic systems exist.156-158 In these and other cases, the intermediacy of a metal imido complex LnM=NR was proposed.159,160 Such a species has recently been isolated (53) and used as a direct catalyst precursor for N-H addition to alkynes and allenes (Scheme 35).161,162... 

Compounds (L)AuR have been used as precursor molecules for the in situ preparation of the strong nucleophiles [(L)Au]+ X- by treatment with strong acids HX (X = CF3S03, CF3C02, BF4, PF6, SbF6 etc. L = tertiary phosphine R = alkyl) in polar solvents (Equation (2)). The solutions are used as catalysts for the activation of alkenes and alkynes for addition of water, alcohols, and amines (Sections 4 and 10). 

Silylstannanes undergo regiospecific addition to alkenes and alkynes with scission of the Sn—Si bond, as illustrated in reactions 15 and 16272. 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

It took another decade however before the idea of developing a rhodium-catalyzed olefin hydroboration process came to fruition. This occurred in 1985 when Mannig and Noth reported the first examples of such a process.8 They discovered that Wilkinson s catalyst 2 was effective for the addition of catecholborane 1 to a range of alkenes and alkynes, as exemplified by cyclopentene 4 (Scheme 2). 

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