Adamantyl , reaction with

The tertiary-secondary 1,2-H shift O itlO is not rate-determining in the interconversion of 5 and 6, but may become so in a conformationally fixed system. It has been found for the interconversion of tertiary and secondary adamantyloxocarbonium ions that <10" sec at 70°C (Hogeveen and Roobeek, 1971a) as compared with k= 1-5 x 10 sec at 20°C for the reaction 5 6. The absence of interconversion between tertiary and secondary adamantyloxocarbonium ions is due to the circumstance that 1,2-H shifts do not occur in the tertiary adamantyl ion as a result of the effect of orbital orientation (Brouwer and Hogeveen, 1970 Schleyer etal., 1970). That the secondary adamantyloxocarbonium ion can lose CO is demonstrated by the reaction with isopropyl cation in SbFs—SO2CIF solution at 0°C with formation... 

Although complete replacement of chlorine atoms can be accomplished with most kinds of amines, this becomes difficult in the reactions with sterically hindered amines. Thus in the reactions of N3P3C16 with cyclohexylamine (71) and adamantyl amine (72), the yields of fully substituted products are low. In the reactions of N3P3C16 with further sterically encumbered amines such as... 

Hindered di-t-alkylamines RNHBu1 (R = t-Bu, t-octyl or 1-adamantyl) have been synthesized from t-alkylamines as follows. Reaction with peracetic acid gave the nitrosoalkanes RNO, which were treated with t-butyl radicals, generated from t-butylhydrazine and lead(IV) oxide, to yield t-butyloxyhydroxylamines. Reduction with sodium naphthalide in THF gave the products (equation 12). The di-t-alkyl-amines are inert to methyl iodide and dimethyl sulphate but can be alkylated by methyl fluorosulphonate42. 

Tris[(2-perfluorohexyl)ethyl]tin hydride has three perfluorinated segments with ethylene spacers and it partitions primarily (> 98%) into the fluorous phase in a liquid-liquid extraction. This feature not only facilitates the purification of the product from the tin residue but also recovers toxic tin residue for further reuse. Stoichiometric reductive radical reactions with the fluorous tin hydride 3 have been previously reported and a catalytic procedure is also well established. The reduction of adamantyl bromide in BTF (benzotrifluoride) " using 1.2 equiv of the fluorous tin hydride and a catalytic amount of azobisisobutyronitrile (AIBN) was complete in 3 hr (Scheme 1). After the simple liquid-liquid extraction, adamantane was obtained in 90% yield in the organic layer and the fluorous tin bromide was separated from the fluorous phase. The recovered fluorous tin bromide was reduced and reused to give the same results. Phenylselenides, tertiary nitro compounds, and xanthates were also successfully reduced by the fluorous fin hydride. Standard radical additions and cyclizations can also be conducted as shown by the examples in Scheme 1. Hydrostannation reactions are also possible, and these are useful in the techniques of fluorous phase switching. Carbonylations are also possible. Rate constants for the reaction of the fluorous tin hydride with primary radicals and acyl radicals have been measured it is marginally more reactive than tributlytin hydrides. ... 

Ipso attack has been detected at both a-positions in the reaction of methyl and adamantyl radicals with methyl 5-nitrofuran-2-carboxylate and 5-nitrofuran-2-carbaldehyde. A typical example is shown in Scheme 43. Ipso attack at the carbon bearing the nitro group leads to substitution via the [Pg.617]

ThiocyanatesSodium arenesulfinates, ArS02Na, are converted into aryl thiocyanates, ArSCN in about 60-75% yield by reaction with diethyl phosphorocyanidate in THF, This reaction is also possible with benzyl and adamantyl sulfinates but yields are only about 40%. Alkyl thiocyanates cannot be obtained in this way. 

In addition to the preparations of ethanoadamantane via Lewis acid catalyzed rearrangement of various polycyclic hydrocarbons described above (Section II. A.1), a ring closure reaction of a substituted adamantane has also been developed. Treatment of 2-adamantyl diazoketone with copper results in the intramolecular carbene insertion illustrated in Eq. (48) 14°1. 

The mechanism of this reaction involves an equilibrium between the 1- and 2-adamantyl cations established via intermolecular hydride transfers. Direct 1,2-hydride shifts on the adamantyl nucleus are inhibited by the unfavorable stereo-electronic relationship between the vacant orbital and the migrating group as discussed previously (see Fig. 1) 5 ). The 2-adamantyl cation, once formed, is trapped by water. The resulting 2-hydroxadamantane apparently then undergoes a disproportionation reaction with an adamantyl cation to give adamantanone and adamantane. The overall reaction is summarized in Scheme 15. 

Intermolecular hydride transfers between t-alkyl centres are observed under stable ion solution conditions. These have very low activation enthalpies (Dirda et al., 1979) and accurate rate data are scarce. The simplest reaction, transfer from isobutane to the t-butyl cation in sulphur dioxide, has been shown to be first order in each component, and to have Ea = 15.1 kJ mol 1 and AS = — lBJK moP1 (Brownstein and Bornais, 1971). Adaman-tane catalyses solution hydride transfer between acyclic tertiary centres such as t-butyl, and it is believed that this reflects higher efficiency of hydride transfers to and from bridgehead 1-adamantyl cation. With its non-planar geometry, the non-bonded interactions between alkyl substituents on donor and acceptor are likely to be less than those between two acyclic reactants. If locking of rotation about the C- H- C axis between the reactants does not... 

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