Homoadamantyl

Tertiary 8,9-dehydro-2-adamantyl and 2,4-dehydro-5-homoadamantyl cations... 

The tertiary 5-methyl and 5-phenyl-2,4-dehydro-5-homoadamantyl cations, 26a, were prepared57 by two different routes either from the corresponding alcohols or the corresponding 2-enclassical carbocations with varying degrees of charge delocalization. 

Scheme 4 Acid hydrolysis of NH P-lactam to homoadamantyl P-amino acids...

A further example of the use of acid hydrolysis of the p-lactam nucleus is the transformation of 12 into homoadamantyl p-amino acid derivatives like 13, which are precursors of potential candidates for treatment of cancer and degenerative brain diseases [58] (Scheme 4). 

Although not competitive synthetically with the methods discussed above two interesting applications of ring closure reactions for the synthesis of homoadamantane derivatives have been reported. The first involves trans-annular cyclopropyl participation in the solvolysis of 48 acetolysis gives 3-homoadamantyl acetate as the only observed product (Eq. (32)) 112 Comparison of the acetolysis rate of 48 (2.14 x 10 4 sec"1,25°C) with that of exo-3-bicyclo[3.3.1]nonyl tosylate (5.82 x 10"s sec. 1,25°C) U3>114)... 

Early work in the area of physical organic chemistry revealed that the bridgehead positions of many polycyclic hydrocarbons are unusually inert to solvolysis and to nucleophilic attack 187>. It is now realized that the solvolytic reactivities of bridgehead derivatives of a variety of polycyclic hydrocarbons vary widely. This is illustrated below for the adamantane family. The reactivities range from 3-homoadamantyl (93), the reactivity of which is nearly the same as that found for typical tertiary acyclic analogues (e.g. f-butyl), to 7-methyl-3-noradamantyl (94) 36 9S>10Si 187 ... 

As indicated previously (see Eq. (31)), 1-adamantylcarbinyl tosylate sol-volyzes in buffered anhydrous acetic acid to give 3-homoadamantyl acetate (93 %) and 1-adamantylcarbinyl acetate (7 %) 96). The acetolysis of chiral 1-adamantyl-l -d tosylate (103) has been found to occur with complete retention of configuration in both products (Eq. (80)) 97>. This result suggests... 

Olah et al. (1976a) continued the studies of potentially degenerate secondary cyclopropylcarbinyl cations incorporated into polycyclic carbon skeletons with the preparation of 2,4-dehydro-5-homoadamantyl cation [144 R = H]. This ion and two 5-substituted tertiary derivatives were prepared from the corresponding 5-R-2,4-dehydrohomoadamantyl alcohols [145 R = H, CH3... 

Combination of both 1,2-carbon shifts and 1,2-hydride shifts in the 4-homoadamantyl cation (4-tricyclo[4.3.1.P- ]undecyl cation, [205]) could lead to... 

Another adamantyl system which has recently been studied by Harris and coworkers is the endo-2,4-dehydro-5-homoadamantyl 3,5-dinitrobenzoate (86). The product from... 

Another system where long distance cyclopropyl participation seems to be occurring is in the spiro tosylate 145 shown below which forms homoadamantyl acetate (146) as the only product and also is 5000 times more reactive than cyclohexyl tosylate. 

In the electrolysis of l-(adamantyl)acetic acid in alcohols the only products isolated were the 3-homoadamantyl ethers, possibly formed via the cyclopropenyl cation intermediates (77). The same result in methanol was published by a Russian group ... 

Thermolysis of acetates has been used to synthesize unstable bridgehead alkenes and dienes, which in some cases have been isolated by trapping at low temperatures. For example, the bicyclic acetate (129 equation 60) gave a mixture of bicyclo[3.3.1]non-l-ene (130) and its retro-Diels-Alder product (131) on pyrolysis at 375-4(X) and thermolysis of the 3-homoadamantyl acetate (132) gave a mixture of products whose formation may have been initiated by acetate elimination.Bridgehead dienes are believed to be involved in the formation of products firom the diacetate (133), and novel dienes were isolated from pyrolysis of acetate (134). ... 

The [2,1,3]-elimination of ethanol from the aziridine 224 is clearly base-induced (mesityl-magnesium bromide) and forms 225 (77 %)122). In the ester cleavage of homoadamantyl acetate (226, gas phase), both possibilities of the [2,l,3]-elimination are observed, i.e. Ct—C-migration leads to 227 (30%), C—H-migration to 228 (5%)123>. 

Methyl substituted adamantyl cations have also been studied103. The bridgehead homoadamantyl cation 42 has been obtained104 from both adamantylcarbinyl and homoadamantyl precursors. Bridgehead bicyclo [4.4.0] decyl, bicyclo [4.3.0] nonyl... 

Adamantyl and Homoadamantyl Cations. The 2-adamantyl system is exceptional among sec-alkyl substrates since it solvolyzes without nucleophilic solvent participation (Section 7.2.1). The extent of anchimeric assistance is more difficult to evaluate. Some evidence is consistent with a weakly bridged intermediate ... 

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