Indene oxides acid-catalyzed hydrolysis

Mechanisms of acid-catalyzed hydrolysis of 1-phenylcyclohexene oxides, indene oxides and 1,2,3,4-tetrahydronaphthalene-l,2-epoxides 264... 

Acid-catalyzed hydrolysis of indene oxides transition-state effects on stereochemistry of diol formation 266... 

ACID-CATALYZED HYDROLYSIS OF INDENE OXIDES TRANSITION-STATE EFFECTS ON STEREOCHEMISTRY OF DIOL FORMATION... 

The cis/trans hydrolysis ratio from the acid-catalyzed hydrolysis of indene oxide (53a, Scheme 17) is 75 25,62,63 and that from acid-catalyzed hydrolysis of 5-met-hoxyindene oxide (53b) is 80 20.61 Thus, the introduction of a methoxy group into position 5 does not result in any significant change in the cis/trans hydrolysis ratio. There is evidence that 54b, which is stabilized by the 5-methoxy group, is sufficiently stable to be trapped by external nucleophiles. The very similar cis/tram diol product ratio from acid-catalyzed hydrolyses of both 53a and b suggest that 54a is also a discrete intermediate. 

The cis and trans diols 55b and 56b are sufficiently reactive in dilute acid solution to undergo equilibration, and the tram diol was determined to be more stable than the cis diol by a factor of 3. In this system, therefore, the major diol from acid-catalyzed hydrolysis is the less stable isomer. This result contrasts with the results from acid-catalyzed hydrolysis of phenyl-substituted cyclohexene oxides, where the major cis diol product is also more stable than the corresponding trans diol. In the hydrolysis of indene oxides 53a, b, therefore, effects that are present in the transition state but absent in the products must play major roles in controlling the cis/trans product ratio. 

The stereochemical outcomes of the acid-catalyzed hydrolyses of 1,2,3,4-tetrahy-dronaphthalene 1,2-oxide 59a and its 6-methoxy derivative 59b (Scheme 18) are quite different from those of the corresponding indene oxide systems. For example, acid-catalyzed hydrolysis of 59a yields only 5% of cis diol 61a and 95% of tram diol 62a.66 However, acid-catalyzed hydrolysis of its 6-methoxy derivative 59b yields 80% of cis diol 61b and 20% of tram diol 62b.67 One might argue that carbocation 60a does not have a sufficiently long lifetime compared to solvent relaxation, whereas 60b does, and that this difference in lifetime leads to different mechanisms... 

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