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

On Rearrangements by Cyclialkylations of Arylpentanols to 2,3‐Dihydro‐1 H ‐indene Derivatives. Part 3. The Acid‐Catalyzed Cyclialkylation of 3,4‐Dimethyl‐ and 3‐( ² H ₃ ]Methyl)‐4‐methyl‐3‐phenylpentan‐2‐ol The cyclialkylation of 2‐(²H₃]methyl)‐4‐methyl‐4‐phenyl1,1,1‐²H₃]pentan‐3‐ol ( 4 ) yielded a 1 : 1 mixture of 1,1‐di(²H₃]methyl)‐2,3‐dimethyl‐1H‐indene ( 5 ) and of 2,3‐dihydro‐2,3‐di(²H₃]methyl)‐1,1‐dimethyl‐1H‐indene ( 6 ) (Scheme 1) 1]. However, it was not clear whether the transposition takes place through the successive migration of a Ph, a Me and again the Ph group (Scheme 2, Path A: shift IV → VII → VIIa ) or through Ph‐, Me‐, and then i‐Pr‐group (Scheme 2, Path B: IV → VII → VIIb ). The cyclialkylation of 3‐(²H₃]methyl)‐4‐methyl‐3‐phenylpentan‐2‐ol ( 7 ) yielded only one product, the 2,3‐dihydro‐2‐(²H₃]methyl)‐1,1,3‐trimethyl‐1H‐indene ( 8 ), in accordance with the migrations according to Path A. This result is also a support for the total mechanism proposed for the cyclialkylation of 4 (Scheme 2). The transition of a tertiary to a secondary carbenium ion is not definitely ensured (see 1]).