Neopentyl derivatives

The tris-neopentyl Mo(VI) nitride, Mo(-CH2- Bu)3(=N) [134], reacts with surface silanols of silica to yield the tris-neopentyl derivative intermediate [(=SiO)Mo (-CH2- Bu)3(=NH)] followed by reductive elimination of neopentane, as indicated by labeling studies from labeled starting organometallic complex, to yield the final imido neopentylideneneopentyl monosiloxy complex [(=SiO)Mo(=CH- Bu)(-CH2 - Bu)(=NH)] [135]. The surface-bound neopentylidene Mo(VI) complex is an active olefin metathesis catalyst [135]. Improved synthesis of the same surface complex with higher catalytic activity by benzene impregnation rather than dichlorometh-ane on silica dehydroxylated at 700 °C has been reported [136],... 

In an approach similar to the synthesis of 12, the neopentyl derivatives [(Me3CCH2)3Zn] K(C6H6) (17) and [(Me3CCH2)3Zn]Na (18) have been prepared from the reaction of (Me3CCH2)2Zn and potassium and sodium, respectively. Also, the structures of these compounds were crystallographically determined and are closely related to the structures of the (trimethylsilyl)methyl zincates described above . 

These reactions are not often important for synthesis because the products, ROH, RSH, and RX, can be obtained more conveniently and directly from alkyl halides by SN1 and SN2 displacement reactions, as described in Chapter 8. However, when both SN1 and Sr,-2 reactions are slow or otherwise impractical, as for neopentyl derivatives, the Grignard reactions can be very useful ... 

The stepwise reduction of the ethynyl complex Fe(C=CH)(dppe)(fj-C5H5) to the neopentyl derivative has been achieved by two sequences of methylation and hydride additions, illustrating the propensity for nucleophilic addition to C , and electrophilic addition to Cfi (25). The initial conversion to [Fe(=C=CMe2)(dppe)(i/-C5H5)]+ (5) has been described above (Section III,A,2) further reactions of this complex with Na[HB(OMe)3], Me30+, and NaBH4 afford the neopentyl complex ... 

A complication of the preceding analysis is that the Co—C bond length also increases in neopentyl derivatives [114-116,127], For isopropyl derivatives the Co—C bond length increases [161,162], simulating a direct lengthening, and as expected, the compounds are relatively unstable. However, there is no evidence that enzymes can induce such lengthening. 

Successful substitutions at neopentyl-type substrates can be performed, but can be accompanied by rearrangements. The best results are obtained with small nucleophiles, for example halides, azide, or cyanide. Some representative examples are shown in Scheme 4.20, to illustrate the reaction conditions required. If electron-rich nucleophiles such as thiolates are used, substitutions at neopentyl derivatives can also occur via SET [95],... 

First order kinetics are also consistent with a sequence which involves rate-determining dissociation of the ion-pair (Figure 2, k <stability depends on the relatively slow... 

Dauben and coworkers observed unusual rate accelerations and ring-expansion rearrangements in the solvolysis of bicyclo[2.2.0]hexane-l-methyl / -nitrobenzoate, in agreement with Winstein s proposed nonclassical cyclobutylmethyl cations (Figure 3). ° Thus, the rate of the solvolysis of bicyclo[2.2.0]hexane-l-methyl p-nitrobenzoate is 7 x 10 times faster than that of the corresponding extrapolated rate for neopentyl derivative. The lack of scrambling of the label in the solvolysis of the 0-labeled... 

X-ray studies have established that the neopentyl derivative As(CH2CMe3)Br2 is trigonal bipyramidal. ... 

Methyl migration in the solvolysis (X=OTs)454), deamination (X=N2)4SS, and deoxidation (X=0CX)456 of chiral neopentyl derivatives (612a) proceeds with >85% inversion at the migration terminus. The stereochemical results, somewhat obscured by uncertainties about the maximum rotation of (616), are consistent with... 

Marks has examined the reactivity of thorium metallacycles with hydrocarbons, where ring strain is used to provide the thermodynamic driving force for alkane activation in a reaction with methane (Eq. 17). Reaction with CD4 shows a dramatic kinetic isotope effect, with kH/kD=6, which is typical of the four-centered electrophilic transition state hydrocarbon activations [76]. The metallacy-cle is formed by the elimination of neopentane from the bis-neopentyl derivative [77]. Reaction with cyclopropane and tetramethylsilane gave the bis-cyclopropyl product Cp 2Th(c-propyl)2 and the bis-TMS product Cp 2Th(CH2SiMe3)2, respectively [78]. 

TAS-F, DMA, 100°C, 85% yield. " The following example cleaves a very hindered neopentyl derivative. 

Acrylamide 1 was synthesized [4] and telomerized with four different alkyl iodides and allyltributylstannane (Fig. 3). GC and HPLC were used to determine selectiv-ities in the = 1 (2 and 3) and n = 2 products (4-7). For the n = 1 products, both diastereomers separated in all cases. However, for the n = 2 products, only the neopentyl-derived telomers (4a-7a) would separate by GC for all four diastereomers in all of the other telomer mixtures, two of the four diastereomers co-eluted or incompletely separated. The results are summarized in Table 2. 

Even more sterically hindered tertiary amines were studied by Lunazzi and coworkers . In a series of iV,iV-diisopropyl , A-t-butyl-neopentyl and N-t-butyladamantyl amines " some of the NMR detectable dynamic processes are of inversion-rotation type. Scheme 3 summarizes the possible interconversions in the diisopropyl series For the neopentyl derivative 38 for example, the DNMR ( H and shows two successive processes during the cooling procedure, with barriers of 8.9 and 7.7 kcalmol . MM2-82 calculations of 39 define 3 possible rotamers around the R—C—N—Ip dihedral angle (Figure 4). Since the G+ and gauche and gauche ) are... 

The insertion of an olefin into a C—M bond is a critical step in some olefin dimerization and polymerization reactions (Section IV,D), but studies of this reaction have not been very fruitful. The insertion of isobutylene into the C—Ti bond of CH3TiCl3 to give a neopentyl derivative is one of the few straightforward examples of this reaction (133). Olefin, diene, and acetylene insertion in acylcobalt compounds have been reported by Heck in an elegant series of papers sununarized in his review of this area (3). These insertions are often quite complex, as illustrated by the butadiene insertion. 

A symposium was held on the theoretical and experimental reactivity of the radical anions of halide compounds." In particular, the reactivity of neopentyl chloride and other neopentyl derivatives was studied in relation to inter- and intra-molecular electron-transfer reactions. 

Table 1 Ionization energy (IE) and relative intensity (rel. int.) in the 70 eV mass spectra of some neopentyl derivatives (CH3)3C-CR2-Y and jS-phenethyl derivatives C6H5-CH2-CH2-Y...

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