Bicyclo hexyl-6-tosylate

Trishomoaromatic Cations. Following Winstein s proposal1058 1061 of the formation of a trishomoaromatic cation in the solvolysis of s-bicyclo[3.1.0] hexyl tosylate, extensive effort was directed toward its generation under stable ion... 

Winstein and coworkers have thoroughly studied the solvolysis of 3-bicyclo-[3.1.0]hexyl tosylates. These investigations provide strong evidence that ionization of the c/>isomer [240 R = OTs] proceeds primarily through the... 

The initial report by Winstein and coworkers " in 1959 that cis-3-bicyclo[3.1.0]hexyl tosylate (108) undergoes solvolysis with cyclopropyl participation to give a homoaromatic trishomocyclopropenyl cation (109), opened up a large new area of... 

Since the major reviews covering the parent 3-bicyclo[3.1.0]hexyl system appeared in the mid-1970s, several other papers dealing with the system have appeared. In one of these, Mjoberg and coworkers have concluded from analysis of far infrared and microwave data that the bicyclo[3.1.0]hexyl system exists in a boat form in its most stable conformation, and that the chair form in which cyclopropyl participation takes place must be vibrationally highly excited. Also, Walkowicz " has reported some further investigations of the influence of alkyl substituents on the chemistry of 3-bicyclo[3.1.0]hexyl tosylates. 

The proposal that cyclopropyl participation in solvolysis of the cis-3-bicyclo[3.1.0]hexyl tosylate (108) proceeds via a trishomocyclopropenyl cation intermediate (109) has been firmly established by product, deuterium scrambling and salt effect studies However, because the cyclopropyl participation in this system requires an unfavorable conformation, it is not apparent from simple kinetic studies. Thus, the cis-3-bicyclo[3.1.0]hexyl tosylate (108) has an acetolysis rate which is only nine times faster than that of the non-participating trans isomer, 110. However, when the 3-bicyclo[3.1.0]hexyl moiety is incorporated into a tricyclic or tetracyclic structure which locks it into a chair form, dramatically large rate enhancements are found. Some examples from the literature which are provided in the review by Haywood-Farmer are given below. These... 

The trishomocyclopropenium ion (CeH/, 199) was first proposed by Winstein and coworkers as an intermediate in the solvolysis of czs-bicyclo[3.1.0] hexyl tosylate and extensive efforts were directed toward its generation under stable ion conditions. The persistent cation 199 was first prepared by Masamune et al. by the ionization of czx-bicyclo[3.1.0]hexane in superacid media and it has since been generated from the corresponding alcohol [Eq. (5.29)]. The NMR spectra of structure 199 are consistent with an ion of Csv symmetry. The three equivalent C-H groups are found at high field in the C NMR spectrum (8 C 4.9,7c h = 195.4Hz) in accordance with their hypercoordinate environments. 

Winstein suggested 1959 that the acetolysis of cis-bicyclo[3,l,0]hexyl tosylate SS9 involves the intermediate formation of a so-called trishomocyclopropenyl cation 700-702) equatorial isomer was found to solvolyse 50 times as fast as the axial 540 the quantitative product of the reaction is only cis-acetate 541 with about... 

The solvolysis of tosylate obtained from bicyclo[2,l,l]hexane-2-ol-2-d, resulted in bicyclo[2,l,l]hexyl-2-acetate in which deuterium is equally distributed between the alcoholic carbon and the neighbouring bridge-head carbon which is in good agreement with the NMR spet a data. 

These data also agree with Brown s results on the solvolysis of 2-aryl-2-bicyclo-[2,l,l]hexyl-p-nitrobenzoates for which the value of was found to be —4.31, i.e. still more negative than that of 2-aryl-2-endo-norbomyl-p-nitrobenzoates (q = —3.72). The acetolysis rate of the secondary tosylate 142 is 3 times as low as that of 2-endo-norbomyl tosylate and 1000 times as low as that of 2-exo-epimer i.e. there are no data in favour of kinetic acceleration due to a-participation. 

Table II. Solvolysis of Some Bicyclo[3,l,0]hexyl-3-tOsylates...

Interesting data have been obtained from the solvolysis of alkyl-substituted bicyclo[3,l,0]hexanes The high solvolytic activity of cis-epimers in comparison with trans-epimers, the stereochemistry of this reaction and the equilibration of deuterium in the products testify to the intermediate formation of trishomocyclo-propenyl cations upon acetolysis of cis-raonomethyl- and dimethylbicyclo[3,l,0]-hexyl-3-tosylates. 

Scheme 8.78. A representation of the (allowed) disrotatory ring opening accompanying solvolysis of endo-bicyclo[3.1.0]hexyl-2-ol tosylate to produce cyclohexene-3-ol acetate (see Schoellkopf, U. Chem. Ber., 1966, 99, 3391 and SchoeUkopf, U. Fellenberger, K. Patsch, M. Schleyer, P. V. R. Su, T. Van Dme, G. W. Tetrahedron Lett., 1967, 3639).

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