Adamantyl substrates

Intermolecular amination experiments described by Muller using 02NC,5H4S02N=IPh (NsN=IPh) as the nitrene source underscore the value of certain rhodium(II) catalysts for C-H insertion (Scheme 17.5) [12, 34—36]. In accord with Breslow s finding, dirhodium carboxylates were demonstrated to catalyze the amination of allylic, benzylic, and adamantyl substrates. Notably, structurally related tetracarboxamide dimers fail to give... 

The convenient synthesis of adamantane [26] led to several significant developments. 1 -Adamantyl substrates (54, Scheme 2.19) are tertiary alkyl compounds for which the caged structure prevents rear-side nucleophilic attack, and elimination does not occur because adamantene (55) is too highly strained. The following question arises when does product formation occur in the solvolytic process Product studies from competing nucleophilic substitutions in mixed alcohol-water solvent mixtures have provided an answer. To explain the background to this work, we first need to discuss product selectivities. 

Scheme 2.19 Non-formation of adamantene (55) from 1-adamantyl substrates.

A final example of the utility of adamantyl substrates as model systems in mechanistic investigations is provided by 1-adamantylcarbinyl derivatives. Detailed product and rate constant determinations of 1-adamantylcarbinyl solvolyses have been interpreted relative to the mechanism of the solvolysis reactions of neopentyl systems in general. 

Finally, microbiological hydroxylation has been shown to be highly stereoselective and stereospecific using adamantyl substrates 369. ... 

Yx values for different leaving groups X have been defined using m= 1.00 for the solvolyses of 1-adamantyl substrates (X = Cl [153], Br [153], I [161], picrate [162], and SMe2 [163]) and 2-adamantyl substrates (X = OTs [44, 158], OCIO3 [162, 166], OSO2CF3 = OTf [164, 166], and pierate [166]). Additional Fqts values have been obtained from solvolyses of 1-adamantyl tosylate (X = OTs [158, 162]). Further FoTf values for trifluoromethanesulfonates (triflates) have been determined from the sol-... 

Reaction of [Ru(TPP)(CO)] (TPP = tetraphenylporphyrin) with PhI=NTs generates a Ru(VI) bis-imido complex, which has been crystallographically characterized [62]. This species is chemically competent as an N-centered oxidant, and will react with olefin, benzylic, and adamantyl substrates to form sulfonylaziridine and sulfonamide products, respectively (Fig. 11). The availability of this meta-stable adduct has offered a unique opportunity to study directly the mechanism of the C-H... 

A mechanistic model involving nucleophilic assistance, but not taking into account the variable electrophilic assistance in different solvents, has been proposed (54, 55) for the solvolysis of tert-butyl halides. The analysis was based on a comparison of solvent effects on the solvolysis rates of tert-butyl and adamantyl substrates. The solvent properties were analyzed in terms of parameters N and Y the electrophilic assistance was incorporated into Y (54, 56). Such an approximation had been acceptable in the original wor4c (14-16), which dealt mostly with aqueous alcohols as solvents. This approximation is no longer permissible when materials like TFA and fluori-nated alcohols are used as solvents. In fact, Fainberg and Winstein (56) pointed out that different solvent mixtures could not be placed on the same correlation line. 

The difference in behavior between tert-butyl and adamantyl substrates, observed essentially in solvents of low nucleophilicity but high anion-stabilizing power, is most probably due to the higher susceptibility of the cage substrate to the electrophilic assistance. In reference 18, we presented other known examples of reactions in which the increased sensi-... 

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