Cyclohexenyl tosylate

It is evident from the foregoing sections that simple alkylvinyl halides do not react via an Sn 1 mechanism, if at all, even under extreme solvolytic conditions (146,149). More reactive leaving groups, such as arylsulfonates, were clearly needed to investigate the possible solvolytic behavior of simple alkylvinyl systems, but the preparation of vinyl sulfonates until recently was unknown. Peterson and Indelicato (154) were the first to report the preparation of vinyl arylsulfonates via reaction of the appropriate disulfonate with potassium t-butoxide in refluxing f-butanol. They prepared and investigated the solvolysis of 1-cyclohexenyl tosylate 169 and c/s-2-buten-2-yl tosylate 170 and the corresponding p-bromobenzenesulfonates (brosylates). Reaction... 

Under similar conditions the 3-cyclohexenyl tosylate 235 is formolyzed with only 40 % retention of configuration i.e. the n-participation is more effective if a symme-... 

This interpretation is supported by results on the acetolysis of the bicyclic tosylates 9 and 10. With 9, after three months in acetic acid at 150°C, 90% of the starting material was recovered. This means that both ionization to a cyclopropyl cation and a concerted ring opening must be extremely slow. The preferred disrotatory ring-opening process would lead to an impossibly strained structure, the /ran -cyclohexenyl cation. In contrast, the stereoisomer 10 reacts at least 2x10 more rapidly because it can proceed to a stable cis-cyclohexenyl cation ... 

With larger bicyclo[n. 1. OJalkyl cyclopropyl derivatives such as 8 and 9, their solvolytic behavior follows from that of the simple alkyl-substituted cyclopropyl derivatives. With smaller bicyclo[n.l.0]alkyl cyclopropyl derivatives such as 10 and 11, however, where a trans-a y cation cannot be accommodated in the ring, the order of reactivity is reversed. In both the [6.1.0] and [3.1.0] examples mentioned above, the rates are given relative to cyclopropyl tosylate. The much higher reactivity of the endo-[3.1.Qi] system (11) over the endo-[6.1.0] system (9) reflects the stability of the almost strain-free cyclohexenyl allylic cation versus the cyclononenyl allylic cation which possesses both torsional and transannular strain. 

Homoallylic participation was first invoked by Shoppee to account for the high rates and the stereospecificity of 3/3-(415) and i-cholesteryl (416) interconversions339). The double bond in (415) is clearly restricted to participation by one end. We cannot distinguish, however, between a homoallylic and a cyclopropylcarbinyl cation as the intermediate [cf. (387) and (355)] because both would be chiral. The same limitations apply to the 3-cyclohexenyl system. The tosylate (417) acetolyzes slightly more slowly than cyclohexyl tosylate340). The products include the acetate (418) corresponding to the starting material, the bicyclic acetate (419), and (420) as a result of hydro-... 

The 4-cyclohexenyl ion provides an example of the dependence of the extent of rearrangement on reaction conditions. Acetolysis of the tosylate gives considerable hydride shift to the more stable allylic ion as well as a little cyclization to a bicyclo[3.1. Ojhexane derivative ... 

The Rh-catalyzed annulation of triazoles has been explored by several investigators as a novel indole synthesis. Fokin s team generated azavinyl carbenes with rhodium and parlayed this reaction into an indole synthesis (equation 3) [54], Davies and colleagues described a one-pot indole synthesis from tosyl azide and cyclohexenyl derivatives involving an in situ triazole formation (equation 4) [55], and Lin reported a synthesis of 3-indolylimines using a similar approach (equation 5) [56]. Miura and coworkers effected the Rh-cat-alyzed intramolecular synthesis of 3,4-fused indoles... 

In many systems the occurrence of rearrangement processes is evident from the structure of the products. Many neopentyl systems, for example, react to give r-pentyl products. This is very likely to occur under solvolytic conditions but can be avoided by adjusting reaction conditions to favor direct substitution, for example, by use of an aprotic dipolar solvent to enhance the reactivity of the nucleophile. The 4-cyclohexenyl ion provides another example of the dependence of the extent of rearrangement on reaction conditions. Acetolysis of the tosylate gives some product resulting from hydride shift to the more stable allylic ion as well as a trace of the bicyclo[3.1.0]hexane product arising from participation of the double bond. ... 

The rate of acetolysis of bicycUc tosylates 48 and 49 with acetic acid at 150 °C depends on the geometry of the generated aUyl cation. Isomer 49 reacts about 2 X 10 times faster than 48 because in the former the reaction proceeds via the formation of stable cis-cyclohexenyl cation [28]. 

Although the homoallylic- cyclopropylcarbinyl cyclization is well-precedented in carbonium ion chemistry (101, 102) there seem to be no reports of the direct cyclization of the tertiary 4-terpinenyl carbonium ion. However, deamination of cyclohex-3-enyl amine and solvolysis cyclo-hex-3-enyl tosylate gives exo- and n /o-bicyclo[3.1.0]hex-2-yl derivatives as 6—43% of the products resulting from nucleophilic capture (101, 103, 104). The modest yield of bicyclic products in these reactions apparently is the result of competing nucleophilic capture prior to cyclization and hydride shift to the 2-cyclohexenyl cation. More efficient cyclization occurs in the acetolysis of 2-bicyclo[2.2.2]oct-5-enyl tosylate (49) owing to the rigid boat-like conformation of the precursor (105). The high efficiency of the base-catalyzed cyclization of the epoxide of 4-iso-... 

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