Olefins allenes

Addition of sulfonyl halides to olefins, allenes and acetylenes. . . 1104... 

Unlike ordinary olefins, allene (1,2-propadiene) (1) undergoes thermal dimerization to afford 1,2-dimethylenecyclobutane (2), first reported by Lebedev in 1913 [1], The yield of the dimer 2 was improved up to 95% by Dolbier, who used a benzene solution of 1 for the dimerization reaction [2]. 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

Alike olefins, allenes also undergo palladium mediated addition in the presence of N-H or O-H bonds. Although these reactions show some similarity to Wacker-type processes, from the mechanistic point of view they are quite different. Allenes, such as the cr-aminoallene in 3.69., usually undergo addition with palladium complexes (e.g. carbopalladation in 3.69. and 3.70., or hydropalladation in 3.71.), which leads to the formation of a functionalized allylpalladium complex. Subsequent intramolecular nucleophilic attack by the amino group leads to the closure of the pyrroline ring.87... 

The groups R2N and Cl can be added directly to olefins, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-N-chloroamines and acids.663 These are free-radical additions, with initial attack by the R2NH + radical ion,664 N-Halo amides RCONHX add RCONH and X to double bonds under the influence of uv light or chromous chloride.665 For an indirect way of adding NH2 and I to a double bond, see 5-32. 

Dioxiranes are three-membered cyclic ring peroxides that are expected to be very unstable owing to ring strain. They are effective oxygenating agents for epoxidations of olefins, allenes, polycyclic aromatic hydrocarbons, enols. and a, /i-unsaturated ketones for insertions of oxygen into X—H... 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

Allenes n-Butyllithium. Methyllithium. Olefin - allene Phosphorus tribromide. 

Because of their kinetic inertness, Pt11 complexes of the type PtCl2L2 allow separation of optical isomers of olefins, allenes, tertiary phosphines or arsines. The complexes are optically stable at 25° and the enantiomorphic forms can be separated by suitable manipulations.26... 

Transition metal-mediated cycloaddition and cyclization reactions have played a vital role in the advancement and applications of modem synthetic organic chemistry. Rhodium-catalyzed cycloadditions/cyclizations have attracted significant attention because of their versatility in the transformations of activated and unactivated acetylenes, olefins, allenes, etc. These reactions are particularly valuable because of their ability to increase molecular complexity through a convergent and highly selective combination of acyclic components. In addition, these reactions allow for the preparation of molecules with chemical, biological, and medicinal importance with greater atom economy. Recent developments in rhodium-catalyzed cycloaddition and cyclization reactions are described in this section. 

Oxidative fluorination of olefins, allenes, and acetylenes are reported [11,12]. The reaction of OF2 with olefinic fluorocarbons is used for the synthesis of fluoropolymers [13]. 

The B-allyl-9-BBN derivatives formed by hydroboration of allenes are utilized for addition of the allyl group to the carbonyl moiety of aldehydes, ketones, and other carbonyl derivatives (allylboration). Since allenes are easily prepared from corresponding olefins [12, 13], the route the olefin-allene-allylborane-carbonyl addition adduct is a general allylation procedure, which provides an attractive alternative to Grignard-based sequences for the syntheses of complex structures. 

Since allenes are easily obtained from the corresponding olefins [6, 7], the route olefin-allene-allylborane-carbonyl addition is general sequence and is a viable alternative to Grignard-based process for the synthesis of complex structures. 

Carbon-nitrogen bond formation is an important subject in the organic synthesis [301], and hydroamination is an atom-efficient process for the generation of amines and imines from olefins, allenes, and alkynes. Titanium-mediated hydroamination was among the most useful protocols thus far developed for this reaction. By using unsymmetrical olefins and alkynes, the addition of HNR2 can in principle lead to two isomeric products, where the isomeric ratio is usually dependent on the type of titanium catalyst used. 

As well as undergoing dimerizations and cycloadditions with olefins, allenes add to ketens to give methylenecyclobutanones in good yields. t-Butylcyano-keten has been added to (+)-cyclonona-1,2-diene, and two diastereoisomers were isolated and shown to be optically active. The retention of optical activity and the fact that the predominant diastereoisomer is the less stable have been presented as evidence in support of a concerted [ 2, -h, 2j mechanism. (The extent of retention of optical activity is not known and the ratio of major to minor products was only 3 2). (S)-( — )-Cyclonona-1,2-diene has been added to dimethylketen. After hydrogenation and base-catalysed equilibration at... 

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