484001-20-9Relevant articles and documents
On rearrangements by cyclialkylations of arylpentanols to 2,3-dihydro-1H-indene derivatives. Part 5. The acid-catalyzed cyclialkylation of 2-(2-chlorophenyl)-2,4-dimethylpentan-3-ol
Fathi, Behrouz,Giovannini, Edgardo,Pasquier, Pierre
, p. 2089 - 2104 (2007/10/03)
The mechanism proposed in [1] to explain the surprising result of the cyclialkylation of 4-(2-chlorophenyl)- 2,4-dimethylpentan-2-ol (3, R = Me), which gives not only the 'normal' product, i.e., the 4-chloro-2,3-dihydro-1,1,3,3-tetramethyl- (4), but also the isomer trans-4-chloro-2,3-dihydro-1,1,2,3-tetramethyl-1H-inden (5), could be differentiated in two sections (cf. Scheme 2): the first from 3 to the intermediary ion IIa?IIb, and the second from the latter ions to the final product 5. For the first section, a sufficiently satisfactory explanation has been given in [1]; the second section has received important support from the mechanisms of the cyclialkylation of 2,4-dimethyl-2-phenylpentan-3-ol (6), the precursor of II′a, the ion IIa without the o-Cl substituent (cf. Schemes 2, 3 and 5 and [4]). The present communication gives an explanation of the influence of the o-Cl substituent: a mechanism is proposed for the very complex cyclialkylation of 2-(2-chlorophenyl)-2,4-dimethylpentan-3-ol (11; cf. Scheme 9). Both mechanism may be considered as definitive. It is very surprising that, by the cyclialkylation of the compounds 1, 3, 8, 11, 15, and 17, only compound 1 gives the 'normal' product: the cyclialkylation of all other phenylpentanols follows complex pathways including Et, i-Pr, and Ph migrations, which could not be expected. In addition, it has been established that the transformation of 21 to 22 (cf. Scheme 12) and that of 23 to 24 (cf. Scheme 13) occur through two consecutive 1,2- and not through a single 1,3-hydride migration or through an elimination-addition process (cf. Scheme 13). It can be assumed that the transformation of ion IV (the 2-(2-chlorophenyl)-3,4-dimethylpent-2-ylium ion) to the ion V (the 4-(2-chlorophenyl)-3,4-dimethylpent-2-ylium ion (both shown in Scheme 9 as D-isomers) occurs through the same pathway.
