E. Giovannini

Über Umlagerungen bei der Cyclialkylierung von Arylpentanolen zu 2,3-Dihydro-1H-inden-Derivaten, 1. Mitteilung

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3-Dihydro-1H-indene Derivatives. Part 1. An Unexpected Rearrangement by the Acid-Catalyzed Cyclialkylation of 4-(2-Chlorophenyl)-2,4-dimethyl pentan-2-ol under Formation of trans-4-Chloro-2,3-dihydro-1,1,2,3-tetramethyl-1H-indene The acid-catalyzed cyclialkylation of 2,4-dimethyl-4-phenylpentan-2-ol led exclusively to the expected product, 2,3-dihydro-1,1,3,3-tetramethyl-1H-indene. However, analogous cyclialkylation of 4-(2-chlorophenyl)-2,4-dimethylpentan-2-ol (1) gave a ca. 1 : 1 mixture of 4-chloro-2,3-dihydro-1,1,3,3-tetramethyl-1H-indene (2) and of trans-4-chloro-2,3-dihydro-1,1,2,3-tetramethyl-1H-indene (3; Scheme 1). The specific action of the Cl substituent is investigated and a mechanism for this unexpected frame-work transposition proposed.

Über Umlagerungen bei der Cyclialkylierung von Arylpentanolen zu 2,3-Dihydro-1H-inden-Derivaten, 2. Mitteilung

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3-Dihydro-1H-indene Derivatives. Part 2. An Unexpected Rearrangement by the Acid-Catalyzed Cyclialkylation of 2,4-Dimethyl-2-phenylpentan-3-ol under Formation of trans-2,3-Dihydro-1,1,2,3-tetramethyl-1H-indene The acid catalyzed-cyclialkylation of 4-(2-chloro-phenyl)-2,4-dimethylpentan-2-ol (1) gave two products: 4-chloro-2,3-dihydro-1,1,3,3-tetramethyl-1H-indene (2) and also trans-4-chloro-2,3-dihydro-1,1,2,3-tetramethyl-1H-indene (3). A mechanism was proposed in Part 1 (cf. Scheme 1) for this unexpected rearrangement. This mechanism would mainly be supported by the result of the cyclialkylation of 2,4-dimethyl-2-phenylpentan-3-ol (4), which, with respect to the similarity of ion II in Scheme 1 and ion V in Scheme 2, should give only product 5. This was indeed the experimental result of this cyclialkylation. But the result of the cyclialkylation of 1,1,1,2′,2′,2′-hexadeuterated isomer [2H6]-4 of 4 (cf. Scheme 3) requires a different mechanism as for the cyclialkylation of 1. Such a mechanism is proposed in Schemes 5 and 6. It gives a satisfactory explanation of the experimental results and is supported by the result of the cyclialkylation of 2,4-dimethyl-3-phenylpentan-3-ol (9; Scheme 7). The alternative migration of a Ph or of an i-Pr group (cf. Scheme 6) is under further investigation.