Allenes, from carbon dioxide

North M (2011) Synthesis of p, y-unsaturated acids from allenes and carbon dioxide. Angew Chem Int Ed 48 4104-4105... 

Similar [2+2] cycloadducts are also obtained from 46 and benzophenone and fluorenone. The reaction of titana allenes with carbon dioxide, ketenes and isocyanates proceeds across the C=0 bonds of the heterocumulenes to give the [2+2] cycloadducts 48. ... 

A solution of 0.20 mol of butyl lithium in about 140 ml of hexane was cooled to -6Q°C and 140 ml of dry THF were added. The mixture was cooled to about -80 C (liquid nitrogen bath) and 0.23 mol of the allenic hydrocarbon (see Chapter VI, Exp. 1, 2, 44) was added in 5 min (methylal1ene was added as a 1 1 solution in THF). The solutions were kept for 1 h at -55°C. Into another 1-1 flask (see also Fig. 1, but without a dropping funnel), cooled at -90°C by immersion in liquid nitrogen, was poured a solution of dry carbon dioxide (from a cylinder) in 130 ml of dry THF. This solution was obtained by introducing about 40 g of carbon dioxide (note 1) into the THF at -90°C. The gas inlet was removed from the second flask and the solution of the lithiated allene (still cooled below -60 C) was poured... 

From the beginning of the 1970s unhl the mid 1980s, several examples of the telomerization of dienes with water [76, 77] or methanol [78, 79] to isomeric mixtures of dienols or dienol ethers catalyzed by palladium-phosphine complexes in the presence of carbon dioxide have been reported. Neither the yield nor the selectivity were very high. However, when allene was employed as a diene , 3-methyl-2-meth-ylene-3-buten-l-ol was obtained with fairly good selectivity (up to 98%) (Eq. 6.43) [78]. 

Anodic oxidation of 1,2-dicarboxylic acids as their alkali metal salts in concentrated aqueous solution gives the alkene with the loss of two molecules of carbon dioxide [125]. Succinic acid affords etltene and methylsuccinic acid ptopene [50]. Allene is obtained from itaconic acid and the isomeric methylmaleic and methyl-fumaric acids give propyne... 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

Although the sp-hybridized carbon atoms are commonly found in acetylenes, nitriles, allenes, carbon dioxide, etc., heavy group-14 element analogs of these compounds are very rare [16, 17]. The first silicon compound with a formal s/i-silicon atom, trisilaallene 12, was synthesized as a dark green solid using two-step reactions from stable dialkylsilylene 13 [18] in overall 42% yield (Scheme 5) [19]. Trisilaallene 12 is sensitive to air but thermally rather stable, with a melting point of 198-200 °C. 

For cumulenic skeletons one observes linear correlations of the asymmetric stretching frequencies i>as with the nuclear charges for the series allene (11) (106), N-phenyl-ketene imine (188) (896), and ketene (43) (107), ketene imine 188 (896), dimethylcarbodiimide (213) (108), and phenylisocyanate (218) (110) as well as allene (11), dimethylcarbodiimide (213), and carbon dioxide (204) (109fl) (Fig. 19). From the first two series one sees that the introduction of a nitrogen atom into the cumulenic skeleton has a constant effect of shifting Vas by 100 cm" to longer wavenumbers. 

When 4-MeOPhC(Et)=C=0 is generated at —78 °C from a pseudo-C2-symmetric chiral phosphorous ylide it undergoes a [2-1-2] cycloaddition, followed by carbon dioxide evolution to give allenic derivatives in 80 % yield with a 92 % e,e. ... 

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