2.2- Dimethylpropyl group

As Table 2 shows, 3 -(2-methylpropyl)-taxoid 23a and the 3 -(2-methylprop-l-enyl)-taxoid 23d possess excellent activities comparable to that of docetaxel in both tubulin binding and cytotoxicity assays. It is also obvious that the activity is very sensitive to the bulkiness of the 3 -substituents as observed by the substantial decrease in activity with change of the C-3 moiety from 2-methylpropyl (23a) to the bulkier tran.y-2-phenylethenyI (23b) or 2,2-dimethylpropyl group (23c). 

An improvement of up to 90% ee with 78% chemical yield is possible with baker s yeast if a bulky alcohol moiety, e.g., the 2,2-dimethylpropyl group, is used141. 

Dimethylpropyl group, 66 Dimethyl sulfate, 596 Dimethyl sulfide, 241 Dimethyl sulfoxide as solvent... 

Dimethylpropyl group Neopentyl halides, nucleophilic substitution... 

Methyl 2,2-dimethylpropyl ketone has a methyl group and a 2,2-dimethylpropyl group bonded to a carbonyl group. 

There is one five-carbon group with an lUPAC approved common name that you should also know the 2,2-dimethylpropyl group, commonly called the neopentyl group. 

Here is the dilemma This is a point of difference but carbon atoms must be compared because C > H for both carbons. Comparing atomic mass at the point of difference compares carbon with carbon, so it is not possible to determine the priority. Another rule is required When, and only when, the first point of difference cannot he resolved by atomic mass because the priority atoms are the same, count the number of priority atoms. In this case, Cccc ig compared with the 2,2-dimethylpropyl chain has three carbons at the point of difference, whereas the 2-methylpropyl chain has two carbons at the point of difference. The assignment is (b) for the 2,2-dimethylpropyl group and (c) for the 2-methylpropyl group, making the priority assignment as shown in 22. The absolute configuration of 20 is (S), and the name is 2,2,6-trimethyl-(45 )-heptanol. 

Neopentyl group (Section 3.4) The 2,2-dimethylpropyl group, (CH3)3CCH2-... 

Steric effects are vector quantities. This is easily shown by considering, for example, the pentyl and the 1,1-dimethylpropyl groups which have the same volume but a different steric effect. That of the former is less than half that of the latter. In order to account for this let us examine what happens when a nonsymmetric substituent is in contact with an active site. Consider, for example, the simple case of a spherical active site Y, in contact with a carbon substituent, CZLZMZS, where the superscripts, L, M and S represent the largest, the medium-sized and the smallest Z groups, respectively. There are three possible conformations of this system which are shown in topviews in Figure 1. As all steric interactions raise the energy of the system, the preferred conformation will be the one that results in the lowest energy increase. This is the conformation which presents the smallest face to the active site, conformation C. This is the basis of the minimum... 

Dimethylpropyl group (tertiary) 1,2-Dimethylpropyl group (secondary)... 

The currently available methods for the synthesis of the title compounds are confined to the preparation of homo-1,1-dihalo-1-alkenes 180 while only a few reports are available for mixed 1,1-dihalo-1-alkenes of defined stereochemistry 18u. As the hy-droboration reaction proceeds in a stereospecific manner, the hydroboration-oxi-dation-bromination-debromoboration sequence of 1-chloro-l-alkynes produces selectively (Z)-l-bromo-l -chloro-l-alkenes (Eq. 116),82>. The oxidation with anhydrous trimethylamine oxide of the alkenylborane prior to the addition of bromine is necessary to avoid the competing transfer of one of 1,2-dimethylpropyl group from boron to the adjacent carbon atom. Similar reaction sequence provides 1,1-dibromo-l-alkenes (Eq. 117)182). 

A contraction for secondary isoamyl, abbreviated Sia. This is the 1,2-dimethylpropyl group. Disiamylborane is used for hydroboration of terminal alkynes because this bulky borane adds only once to the triple bond. (p. 412)... 

A related case occurs when there is more than one complex substituent, but they are identical. When identical substituents are substituted in the same way, they may be indicated by the appropriate multiplying prefixes bis, tris, tetrakis, pentakis, etc. The complete expression denoting such a side chain may be enclosed in parentheses or the carbon atoms in side chains may be indicated by prime numbers. For 23, a decane, there are two 1,1-dimethylpropyl groups at C5 and C6, so the term bis is used. Compound 23 is therefore 5,6-6is-(l,l-dimethylpropyl)decane. 

Brown-Hammett correlation of 1-aryl-1-cyclobutylethyl p-nitrobenzoate gave a p+ value of -3.94 which is more positive than that of a model compound, l-aryl-l,2-dimethylpropyl p-nitrobenzoate (p+ = -4.65), which indicates substantial neighboring group participation of the cyclobutyl ring even in tertiary carbocationic systems.12 Solvent effects on the kinetics of the solvolysis... 

The patterns of regio- and stereoselectivities become more complex in disubstituted oxiranes. Beginning with 2,2-disubstituted oxiranes, attack is always at the accessible C-atom. In terms of substrate enantioselectivity, it was found that 2-butyl-2-methyloxirane (2-methyl-1,2-epoxyhexane, 10.43, R = Bu) was hydrolyzed with a preference for the (5)-enantiomer. This substrate enantioselectivity was lost for branched analogues, namely 2-(/er/-bu-tyl)-2-methyloxirane (10.43, R = /-Bu) and 2-(2,2-dimethylpropyl)-2-meth-yloxirane (10.43, R = (CH3)3CCH2) [124], Thus, it appears that the introduction of a geminal Me group suppresses the enantioselectivity seen with branched monoalkyloxiranes, and reverses it for straight-chain alkyloxiranes. 

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