Alkenes, Alkynes and Allenes

Aikenes are usually reduced by catalytic hydrogenation. Diimide reduction is a mild and neutral alternative. Keith R. Buszek, now at the University of Missouri, Kansas City, has shown J. Org. Chem. 2007, 72, 3125) that the reduction can conveniently be carried out on resin-bound aikenes, using 2-NBSH (o-nitrobenzenesulfonyUiydrazide) with Et N for convenient room temperature diimide generation. 

Ozone can be difficult to dispense accurately on small scale. Masahito Ochiai of the University of Tokushima has uncovered J. Am. Chem. Soc. 2007,129, 2772) an alternative, using acid-promoted Ph-I=0. Isolated aikenes also work well. 

MCPBA is the reagent most commonly used for alkene epoxidation. Payne oxidation (H O / CUjCN) is a convenient and inexpensive alternative. In the course of a study of the enantioselective enzymatic hydrolysis of 6, Takeshi Sugai of Keio University has described Tetrahedron Lett. 2007, 48, 979) a practical procedure for multigram Payne epoxidation of 5. 

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Nonstabilized carbonyl ylides (41) prepared by reaction of a-iodosilyl ethers with Smlj, can be trapped with various alkenes, alkynes and allenes to form furans of type 42, 43, and 44... 

B. Hydrocarbyl 7i-complexes 1. rj2-Alkene, alkyne, and allene complexes... 

Halogenated organic compounds may be converted into alkenes, alkynes and allenes by various routes. 

The Sn-P bond also adds to the same polar multiply-bonded acceptors (PhNCO, PhNCS, CS2, and COS) to which Sn-0 and Sn-N bonds add (Section 14.1.3 and 16.1.3.4) (e.g. equation 16-76) these reactions are thought to involve polar 4-centre processes.75 Additions also occur to alkenes, alkynes, and allenes with much less polar... 

Reactions of intramolecular hydroamination of alkenes, alkynes, and allenes with the formation of A-heterocycles in the presence of lanthanocene catalysts 02CRV2161. 

A great variety of sulfones are available from the addition of RSO2X to alkenes, alkynes, and allenes [6, 8, 18, 27-30] (Eqs. 11-16). In the case of cyclic alkenes, the addition is highly stereoselective in favor of the trans adduct (Eq. 11). 

Neutral carbon of organic compounds is inherently a very weak base due to the lack of nonbonding electrons. However, the 7r-system of alkenes, alkynes, and allenes are potential basic sites due to the availability of 7t-electrons. Wooldridge and Roberts [61] first reported the facile photohydration of arylacetylenes to the corresponding ketones (in an overall Markownikoff sense) in dilute aqueous acid solutions. The facile protonation of the excited state was attributed to the enhanced basicity of the alkyne moiety in the excited state, more specifically as a result of extensive charge migration from the aryl group to the acetylene moiety. The photoaddition of methanol [62] and acetic acid to 7c-electron systems such as alkenes, alkynes, and allenes may be rationalized in the same way. 

Aromatic alkenes, alkynes, and allenes undergo intramolecular and intermolecu-lar proton transfer in neutral or dilute aqueous acidic media to give Markov-nikov-oriented hydration products [Eq. (10)] [95,96] ... 

Abstract Progress in the field of metal-catalyzed redox-neutral additions of oxygen nucleophiles (water, alcohols, carboxylic acids, and others) to alkenes, alkynes, and allenes between 2001 and 2009 is critically reviewed. Major advances in reaction chemistry include development of chiral Lewis acid catalyzed asymmetric oxa-Michael additions and Lewis-acid catalyzed hydro-alkoxylations of nonacti-vated olefins, as well as further development of Markovnikov-selective cationic gold complex-catalyzed additions of alcohols or water to alkynes and allenes. 

Reactions with Alkenes, Alkynes, and Allenes. Pentafluorosulfanyl chloride has been used in a free radical chain addition process to alkenes and alkynes. These free radical chain addition reactions have been accomplished thermally (eq 4) in an autoclave or via a room-temperature gas-phase or low-temperature solution-phase photochemical process (eq 5). A... 

Table 2.8 Rates of reaction of dye-functionalized alkenes, alkynes, and allenes with various metathesis (pre)catalysts Alkene Alkyne Allene... 

Neutral group 4 metal complexes appear to possess a relatively broad scope for catalytic hydroaminations. They have been employed for the intramolecular as well as the intermolecular hydroaminations of alkenes, alkynes, and allenes. Catalytic hydroaminations (and hydrohydrazinations) of alkynes have been exploited as key steps in catalytic multicomponent reactions, giving rise to highly functionalized substrates, in particular to several types of N-heterocycles. Chapter 13 by Gade focuses, inter alia, on two case histories involving hydrohydrazinations which exemplify key challenges and the way they may be addressed in practice. 

The development of catalytic methods for the hydroamination of nonactivated alkenes, allenes, and alkynes has received considerable attention in recent years [1]. These highly atom-economical processes allow direct access to industrially and biologically relevant classes of compounds such as amines, enamines, and imines from cheap and readily available starting materials. This has recently led to an ever-increasing range of molecular compounds that have been identified as catalysts for these transformations (Scheme 13.1). Whereas rare-earth catalysts have been found to be mainly active in intramolecular hydroamination, other catalysts - in particular those of the late transition metals - are frequently limited to the addition of weakly basic substrates (aniline, sulfonamides, carboxamides, etc.) to alkenes, alkynes, and allenes. 

Qiu G, Kuang Y, Wu J (2014) N-imide ylide-based reactions C-H functionalization, nucleophilic addition and cycloaddition. Adv Synth Catal 356(17) 3483-3504 Menon RS, Nair V (2014) 4.21 Intramolecular 1,3-dipolar cycloadditions of alkenes, alkynes, and allenes. Compr Org Synth 11 4 1281-1341... 

PALLADIUM-CATALYZED CASCADE REACTIONS OF ALKENES, ALKYNES, AND ALLENES... 

NHC-Cu-catalyzed diborations of styrene and phenylacetylene were first studied by the groups of Perez and Fernandez on the basis of initial studies on the borocupration of unactivated alkenes made by the group of Sadighi. Since these first developments, numerous methods have been developed. It has been shown that carbon n-systems such as alkenes, alkynes and allenes could be variously functionalized by trapping the organocopper species intermediately formed with an external electrophile. 

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