Allenic linkage

There is a host of less common functional groups that involve unsaturated (i.e., multiply bonded) carbon and appear in the same downfield region of the 13C spectrum as carbonyls, for example, the central (sp hybridized) carbon of an allene linkage (C=C=C). Such carbons give very weak signals... 

The data show that the allene becomes more stable than the acetylene as the ring size decreases. This fact seems to be attributable to the Baeyer strain, since in an allene linkage only three carbons must be in a straight alignment compared to fotir in an acetylene. 

Additions. Amines form 2 1 adducts with conjugated enynes to give 1,4-diamino-2-butenes. An intramolecular addition to an allene linkage produces 2-alkenyl heterocycles... 

Intramolecular reaction initiated by ionization of an allylic acetate and participated in by a distal allene linkage can have different ramifications when the molecule is also equipped with another double bond. The separation between this latter double bond and the allene moiety determines the structure of the final product. 

A complex lipid from the seed oil of the Chinese tal-lowtree, Sapium sebiferum (Euphorbiaceae), appears to have arisen in this manner (Fig. 3.8). Although acetylenic compounds are not commonly found in the Euphorbiaceae, the presence of an allenic linkage is suggestive of dieir presence. 

Baudouy, R., and J. Gore New synthesis of a pheromone with a vinyl allenic linkage. Synthesis 1974, 573—574. 

Acceptor-substituted allenes can be prepared from the corresponding propargyl precursors by prototropic isomerization (see Section 7.2.2). Conversely, such allenes can also be used to synthesize propargyl compounds. For example, treatment of the sulfoxides 417 with 1 equivalent of a lithiation reagent leads to the intermediates 418, which furnish propargyl sulfoxides 419 by hydrolysis (Scheme 7.55) [101]. If the electrophiles used are not protons but primary alkyl halides or carbonyl compounds, the products 420 or 421, respectively, are formed by C,C linkage. 

Nucleophilic attack on 45 (R = H) by four equivalents of Li[HBEt3], followed by addition of iodomethane, affords the p-allene complex (48) in a reaction which involves reduction of a coordinated CO and linkage to the vinylidene within the coordination sphere (57, 70) ... 

Even more rare are photocycloadditions involving carbonyl compounds to allenes. Arnold has found that acetone and tetramethylallene can be irradiated to form a mixture of 2-alkylideneoxetane and 1,3- and l,6-dioxaspiro[3,3]heptane products (107 108 109 = 8 31 27), all resulting from initial attack of the carbonyl n,ir state on the central carbon linkage. Hammond subsequently repented a study in which alkylideneoxetane derivatives (111) were photoisomerized to cyclobutanes (110). 

Dearing, J. A., Maher, B. A., and Oldfield, F., 1985, Geomorphological linkages between soils and sediments the role of magnetic measurements, in Geomorphology and Soils, K. S. Richards, R. Arnett, and S. Ellis, eds., George Allen and Unwin, London, pp. 245-266. 

Allen, F. H., Doyle, M. J., and Taylor, R. / Automated conformational analysis from crystallographic data. 1. A symmetry-modified single-linkage clustering algorithm for three-dimensional pattern recognition. Acta Cryst. B47, 29-40 (1991). 

J. G. Allen and B. Fraser-Reid, n-Pentenyl glycosyl orthoesters as versatile intermediates in oligosaccharide synthesis. The proteoglycan linkage region,./. Am. Chem. Soc., 121 (1999) 468-469. 

Pudovik. A.N.. and Aladzheva, I.M., Acetylene-allene-acetylenic rearrangements of phosphites with a p.y-acetylene linkage in the ester radical, Zh. Obshch. Khim., 33, 707, 1963 J. Gen. Chem. USSR (Engl. Transl.). 33. 700. 1963. 

Smith K, Morse M, Mork P, Li M, Rosenthal A, Allen D, Seligman L (2009) The role of schema matching in large enterprises. In CIDR, Asilomar Winkler W (1999) The state of record linkage and current research problems. In Statistics of Income Division, Internal Revenue Service Publication R99/04 Wordnet (2007) http //wordnet.princeton.edu... 

Allenic alcohols. Claesson et al. have prepared organic cuprate reagents by the reaction of Grignard reagents with Cul in the ratio of 4-5 1 eq. in ether at -30° under Nj. These cuprates displace methyl and tetrahydropyranyl ether groups of acetylenic alcohols with shift of the unsaturated linkage to give a- and 0-aUenic alcohols as shown in the examples. 

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