Cyclopropylcarbinyl spiro

That maximum acceleration occurs when the vacant p orbital is parallel to the plane of the cyclopropyl ring can be seen from the solvolysis of spiro[cyclo-propane-l,2 -adamantyl] chloride (71). The carbocation formed by departure of Cl is unable to adopt the geometry of the bisected cyclopropylcarbinyl cation, but can orient its empty p orbital properly to form the bicyclobutonium ion. This compound solvolyzes 103 times more slowly than 1-adamantyl chloride.82 On the other hand, 72 solvolyzes 10s times faster than 73. The cation from 72 does have its p orbital parallel to the plane of the ring as in the bisected cyclopropylcarbinyl cation.83... 

Long-lived cyclopropylcarbinyl cation chemistry, including spiro cations and dications, has been reviewed,7 and some of the more interesting newer carbocations, such as (1), are the subject of a short survey.8 The use of secondary deuterium isotope effects in the study of carbocation-forming reactions has been revisited,9 and the... 

Eq. 3.119 shows the preparation of a spiro compound (289) through 5-exo-trig ring closure to form a cyclopropylcarbinyl radical, followed by (3-cleavage, and subsequent 5-exo-trig ring closure to imino-carbon [299-301]. 

The stabdities of protonated cyclopropylcarbinyl ketones are a long-standing puzzle. Richie provided evidence that the bisected cyclopropylcarbinyl carbenium ion (66a) was the more stable conformation, rather than the perpendicular geometry (66b). Of the protonated, rigid ketones, (67), (68), and (69), spiro compoimd (67) is most stable, but the bicyclo compound (68) proved more stable than the nortricyclic system (69), although the latter has a bisected geometry, while (68) is imable to achieve this. The anomaly appears to have been resolved by semiempirical calculations of heats of formation of the ketones and ions, and an analysis of the effects of syn- and... 

Although the previous reviews adequately cover the effects of simple alkyl substituents in cyclopropylcarbinyl systems, they do not mention the case where the cyclopropane ring is part of a spiro system. Thus, Wilcox and Hsu compared the hydrolysis rate in 70% aqueous acetone at 125°C of 30 having a cyclopropylcarbinyl 3,5-dinitrobenzoate attached spiro to the 7-position of norbornane with that of 3,3-dimethylcyclopropylcarbinyl 3,5-dinitrobenzoate (29). It was found that with a larger spiro ring as in 30, the effect on rate was small ( 29/ 30 = 1 ) No products were reported in this study. 

The Spiro [2,2]pentylmethyl system (31) is of considerable interest. The acetolysis products shown below reveal interesting cyclopropylcarbinyl to cyclobutyl cation and... 

SCHEME 5. Products of hydrolysis of some spiro cyclopropylcarbinyl p-nitrobenzoates in 80% aqueous acetone at... 

An early attempt to achieve the perpendicular cyclopropylcarbinyl conformation by means of t-butyl-substituted spiro[2,5]octyl derivatives was unsuccessful. Thus, the cis isomer (52) with the t-butyl and leaving groups both equatorial was expected to solvolyze much more slowly than the trans isomer (51) having an equatorial t-butyl group and an axial leaving group. However, the small rate difference of 2 1 revealed that the... 

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