Allenes other multiple bonds

Besides alkenes and alkynes, other multiple bonds can be used as acceptors in addition reactions of carbon radicals provided the usual requirements of reactivity and selectivity are met. Other types of carbon-carbon multiple bonds that have been used as acceptors include dienes,162 allenes,61 enolates (and ni-tronates, see below) and quinones.223 Even highly strained cr-bonds have served as acceptors on occasion.224... 

Trimethylamine N-oxide, 325 Vinyltrimethylsilane, 343 Other reactions (Phenylsulfonyl)allene, 247 Cyclodehydration Diethoxytriphenylphosphorane, 109 Hexamethylphosphoric triamide, 142 Cycloprop anation Simmons-Smith reaction Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 by other reagents which add CH2 to a carbon-carbon multiple bond Dibromomethane-Zinc-Copper(I) chloride, 93... 

This behaviour correponds to the observation that other unsaturated hydrocarbons, e.g. alkynes, allenes or 1,3-butadienes, which readily undergo transition metal catalyzed cyclooligomerizations, do also incorporate CX multiple bonds in such cycloadditions only with difficulty in most cases 207 208). Besides the well known cobalt-catalyzed pyridin synthesis from alkynes and nitriles98 cocyclooligomerizations have been achieved with alkynes on one side and isocyanates 209), carbodiimides210) and carbondioxide 211) on the other side as well as with 1,3-butadienes and aldehydes 212), carbondioxide213 and 2-aza- or 2,3-diaza- 1,3-butadiene214. ... 

This behaviour correponds to the observation that other unsaturated hydrocarbons, e.g. alkynes, allenes or 1,3-butadienes, which readily undergo transition metal catalyzed cyclooligomerizations, do also incorporate CX multiple bonds in such cycloadditions only with difficulty in most cases Besides the well known cobalt-... 

The groups capable of polymerization may be of different types, namely, vinyl, allyl, styryl, diene, allenic, acetylenic, acrylic, alkoxide, etc. Also, different rings bonded with metal such as epoxy, ethyleneimine, and others may be used. It goes without saying that multiple bond can be present not only as double bonds but also as triple, allene, diene bonds as well as their combinations. The correlation between the electronic structure and the... 

The structure analysis of diphenylmethylene-aminodimesitylborane PhgC N B(PhMeg)g has shown that the molecule can be considered an analogue of allene. B-N and N-C distances, 1.40 and 1.31 A, respectively, indicate appreciable multiple bonding in each case. The QB and C, planes are virtually perpendicular to each other, as is required by an allenic type of structure. The deviation of the B-N-C angle (170°) from linearity is ascribed to packing effects. 

Another class of hydrocarbons has multiple 7i-bonds the allenes. The parent compound is 20 and is named allene. Formally, 20 is a diene and the lUPAC name is 1,2-propadiene or propan-1,2-diene. Allene is an example of a cumulene—a molecule that has cumulative %-bonds. The term cumulative indicates that there are three or more adjacent sp or sp hybridized carbon atoms. Note that the central carbon has two Ji-bonds and is sp hybridized, whereas the two flanking carbons are sp hybridized. This arrangement requires that the two 7i-bonds are perpendicular—one to the other—as shown in 20B, which positions the methylene units (the -CH2- units) in different planes. 

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