Allenes vinylic

A number of cycloadditions of imines or imino compounds with a variety of alkenes, including allenes, vinyl ethers, enolates, ketene acetals, and electrophilic alkenes, afford functionalized azetidines . 

Marshall, J. A. Synthesis and Reactions of Allylic, Allenic, Vinylic, and Arylmetal Reagents from Halides and Esters via Transient Organopalladium Intermediates. Chem. Rev. 2000, 100, 3163-3185. 

Wender and co-workers have also demonstrated the Rh(I)-catalyzed [5-1-2] intramolecular cycloaddition of disubstituted allene-vinyl cyclopropanes 92 and 94 (96). The reaction afforded the cis-5/7-fused bicyclic compounds, 93 and 95 as the only or major products. The axial chirality of the allene moiety in 92 was transferred with high efficiency to the final product 95 (Scheme 48). 

Marshall JA. Synthesis and reactions of allylic, allenic, vinylic, and arylmetal reagents from halides and esters via transient organopalladium intermediates. Chem. Rev. 2000 100 3163-3186. 

Addition of arylhydroxylamines to electrophilic allenes such as methyl propadienoate or l-methancsulfonyl-l,2-propadiene is another route to 0-vinyl derivatives[2]. The addition step is carried out by forming the salt of the hydroxylamine using NaH and the addition is catalysed with LiO CCFj. The intermediate adducts are cyclized by warming in formic acid. Yields are typically 80% or better. 

Addition of hydrogen halides to simple allenes initially gives the vinyl halide, and if the second double bond reacts, a geminal dihalide is formed. " ... 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

Elimination of hydrogen fluoride from vinylic fluorides yields allenes [2J] or acetylenes [24] (equations 21 and 22)... 

Sulphones (coni.) allenic - see Allenic sulphones allyl - see Allyl sulphones aryl unsaturated alkyl - see Aryl unsaturated alkyl sulphones aryl vinyl - see Aryl vinyl sulphones as radiolytic products 907 bicyclic - see Bicyclic sulphones bis(/ -hydroxyalkyl) - see Bis... 

Allene lassen sich mit Trimethyl-zinnhydrid zu Vinyl- und Allyl-zinn-Derivaten um-setzen, die mit Trifluoressigsaure die entsprechenden Olefine ergeben7 z.B. Buten-(2) ausgehend von Butadien-(1,2) ... 

As in the case of the base-catalyzed reaction, the thermodynamically most stable alkene is the one predominantly formed. However, the acid-catalyzed reaction is much less synthetically useful because carbocations give rise to many side products. If the substrate has several possible locations for a double bond, mixtures of all possible isomers are usually obtained. Isomerization of 1-decene, for example, gives a mixture that contains not only 1-decene and cis- and franj-2-decene but also the cis and trans isomers of 3-, 4-, and 5-decene as well as branched alkenes resulting from rearrangement of carbocations. It is true that the most stable alkenes predominate, but many of them have stabilities that are close together. Acid-catalyzed migration of triple bonds (with allene intermediates) can be accomplished if very strong acids (e.g., HF—PF5) are used. If the mechanism is the same as that for double bonds, vinyl cations are intermediates. 

Although at first glance addition to the central carbon and formation of what seems like an allylic carbonium ion would clearly be preferred over terminal addition and a vinyl cation, a closer examination shows this not to be the case. Since the two double bonds in allenes are perpendicular to each other, addition of an electrophile to the central carbon results in an empty p orbital, which is perpendicular to the remaining rr system and hence not resonance stabilized (and probably inductively destabilized) until a 90° rotation occurs around the newly formed single bond. Hence, allylic stabilization may not be significant in the transition state. In fact, electrophilic additions to allene itself occur without exception at the terminal carbon (54). 

Hydration of allene in sulfuric acid yields acetone, presumably via a vinyl cation intermediate (55, 56). Addition of HCl and HBr to allene results in... 

A summary of electrophilic additions to triple bonds and allenes involving a vinyl cation is given in Table IV. 

Summary of Electrophilic Additions to Acetylenes and Allenes Involving Vinyl Cations... 

Unlike triple-bond participation, no remote cumulative double-bond (allenic) participation in solvolysis has so far been observed or reported. A summary of triple-bond and allenic participation in solvolysis involving possible vinyl cations is given in Table VI. 

All of the above mentioned examples of vinyl cation intermediates have involved electrophilic additions to triple bonds or allenes or participation in solvolyses of such multiple bonds. In a sense, these reactions derive from analogies in normal... 

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