Other Reactions of Allenes

Other Reactions of Allenes.— Radical-chain additions to allenes are presumed to involve radical intermediates of allylic structure by initial attack at the central carbon atom or of vinylic structure by attack at the terminal carbons. The extent to which these structures are preferred depends upon structure of starting allene, nature of attacking radicals, and reaction conditions. Addition of toluene-/ -sulphonyl iodide to chiral allenes (cyclonona-1,2-diene and penta-2,3-diene) results in racemic products (376), and hence attack on 

Caserio, Selective Organic Transformations , ed. B. S. Thyagarajan, Wiley-Interscience, New York, 1970, vol. 1. 

The suggestion by Hine that a stable carbene might be obtained if the electron-deficient carbon is attached to an electron donor and an electron 

Addition of bromine to cyclonona-1,2-diene takes place with formation of transannular bromination products predominating, but no such products are obtained from cyclo-octa-1,2-diene or cyclodeca-1,2-diene.  

For participation of the / -allenic bond in nitrous acid deamination of / -allenic amines, it appears that the amine should be acyclic and substituted in the chain. Singlet-state Cg produced from a carbon arc under high vacuum 

Other Reactions of Allenes.—Allylic halides undergo solvolysis at rates greater than those of their saturated analogues owing to charge delocalization through the Tr-system. The vinyl cation,it may be anticipated, could be 

2-methyl-l-pentyltosylate. Similarly, the bishomoallenic tosylate (216) solvolyses at a rate which suggests that participation is occurring, and the cyclopentene derivatives (217) and (218) are among the products. This 

The allenic dianion (219) is obtained from the acetylene (220) by treatment with two moles of butyl-lithium. Alkylation can be carried out successively using two different reagents to yield the tetrasubstituted allenes (221) hydrolysis of the monoalkylated products yields a -unsaturated aldehydes (222), 

Adsorption of MeC=CD on zinc oxide gives rise to an OH band at 3515 cm in the i.r. spectrum and no band at 2598 cm (OD) is observed, suggesting that the following process is occurring  

The spectrum is identical to that of adsorbed allene, implyingthat the adsorbed species is the propargyl anion. In agreement with this conclusion is the isomerization of allene to methylacetylene when the former is circulated over the activated zinc oxide employed.  

---