Rert 4- -2-methyl

The presence of a tnalkylsUyl group in a fluonnated organic compound may be useful to direct further transformations of that matenal Yet m some instances it IS the fluonnated substituent that controls the reactions of the tnalkylsdyl group Contrary to predictions, treatment of tert-hnlyX 3-tnfluoromethyl-6-tnmethylsilyl-phenyl carbamate with rert-butyllithium results m metallation of one of the methyl groups attached to silicon rather than that of the aromatic nng [90] (equation 75)... 

In an oven dried glass flask under an argon atmosphere at — 78 UC, 950 mg (5 mmol) of methyl 2,3-dihydro-1-oxo-l/f-indene-2-carboxylate in 10 mL of toluene are added to 2.2 mg (0.2 mmol) of potassium rert-butoxide in 5 mL of toluene. 356 mg (0.2 mmol) of (5, 6 )-bis[3,3 -dimethyl-l,l -binaphthalene]-2,2 -diol bis(diethy-lencoxy) ether [(5,.5)-3) are added, followed after 10 min by 700 mg (10 mmol) of 3-buten-2-one in 10 mL of toluene and the mixture is stirred for 120 h at — 78 °C after which it is poured into 35 mL of sat. aq NH4C1. The toluene layer combined with a toluene wash solution is dried over MgS04 and evaporated at 40 "C. The crude adduct is purified by chromatography over silica gel (C H2C12) yield 624 mg (48%) 99% ee. 

For the other alkyl groups, hyperconjugation is diminished because the number of C—H bonds is diminished and in ferf-butyl there are none hence, with respect to this effect, methyl is the strongest electron donor and rert-butyl the weakest. 

Neither methyl nor ethyl fluoride gave the corresponding cations when treated with SbFs. At low temperatures, methyl fluoride gave chiefly the methylated sulfur dioxide salt, (CH3OSO) ShF while ethyl fluoride rapidly formed the rert-butyl and ferf-hexyl cations by addition of the initially formed ethyl cation to ethylene molecules also formed ° At room temperature, methyl fluoride also gave the tert-butyl cation. In accord with the stability order, hydride ion is abstracted from alkanes by super acid most readily from tertiary and least readily from primary positions. 

Figure 13.8.2 2-Methyl-2-propanethiol or rert-butyl mercaptan, an example of an odorant and warning agent for natural gas.

The acyclic version of Larock s heteroannulation was successfully applied to the synthesis of highly substituted pyridines [166]. The annulation of rert-butylimine 210 with phenyl propargyl alcohol produced pyridine 211 regioselectively in excellent yield. The regiochemistry obtained was governed by steric effects. Furthermore, the choice of imines was crucial to the success of the heteroannulations. terr-Butylimine was the substrate of choice, since all other imines including methyl, isopropyl, allyl and benzyl imines failed completely to produce the desired heterocyclic products. 

A more subtle example of identical functional groups with different steric enviroment is found in the intermediate H which Corey [8] uses in the synthesis of fumagillin (13). The two identical secondary hydroxyl groups in the cyclohexane derivative H can be differentiated by using a bulky reagent since the axially disposed hydroxyl group is less accesible than the one which is equatorially disposed and can be chemoselectively methylated (12) in the presence of sodium rert-amylate (Scheme 12.2). 

Figure 17.3. Data for vapor pressure and composition of solutions of methyl rert-butyl ether Pi and chloroform p2 at 313.15 K. Data from Ref. 2.

The crystal structure of ethyl 4-(4-rert-butoxycarbonyl-l-piperazinyl)-5-fluoro-2,3-dihydro-l-methyl-2,7-dioxo-l//,7//-pyrido[3,2,l-iy]cinnoline-8-carboxylate (186, R = Et, R = tert-Qu, R = 4-tm-butoxycarbonyl-l-piperazinyl) was determined by means of X-ray diffraction investigation [95T11125]. 

The stereoselectivity of the reaction can be rationalized in terms of the relative stabilities of the products 133 and 134. The stereoselectivity was more pronounced in the cyclohexane series. The stereoselectivity increases with increasing size of substituent R, and the reaction becomes a stereospecific process for the rert-butyl derivatives. The equatorial position of a bulkier substituent is preferred, and thus in the phenyl series the steric requirement of the phenyl group is smaller than that of the methyl group. 

This strategy was very recently used for the total synthesis of 5-Araneosene. In the first step of the synthesis, methyl rert-butyldimethylsilyl ketone 47 was treated with 2-propenyllithium 48 in ether and then with 2-isopropylallyl bromide 49 in THF to give the (Z)-enol silyl ether 50 in 82% yield. The sequence of reactions that leads to 50 includes (1) carbonyl addition of 48, (2) Brook isomerization and (3) allylation of the resulting ally lie lithium reagent (equation 18) ". ... 

Another direct approach to chiral polymeric stationary phases is the modification of commercially available polysiloxanes which contain reactive side groups. Thus, the diamide phase was linked to a modified XE-60 polysiloxane phase (Table 2). In one case (XE-60-L-Val-(/ or 5)-a-pea)124 another center of stereogenicity (R or S configuration) has been introduced in the amide group. An XE-60-L-Val-(S)-x-pea column was used for the enantiomer separation of racemic. V-rert-butoxycarbonyl amino acids after their methylation with diazomethane (serine and threonine as the O-trimethylsilyl derivatives) (Figure 12)124. 

Rates of radical additions to alkenes are controlled mainly by the enthalpy of the reaction, which is the origin of regioselectivity in additions to unsymmetrical systems, with polar effects superimposed when there is a favorable match between the electrophilic or nucleophilic character of the radical and that of the radico-phile. For example, in the addition of an alkyl radical to methyl acrylate (2), the nucleophilic alkyl radical interacts favorably with the resonance structure 3. Polar effects are apparent in the representative rate constants shown in Figure 4.14 for additions of carbon radicals to terminal alkenes. Addition of the electron-deficient or electrophilic rert-butoxycarbonylmethyl radical to the electron-deficient molecule methyl acrylate is 10 times as fast as addition of... 

Methyl (2/ )-l-(Benzyloxycarbonyl)-2- ( )- and (Z)-3-[(rert-butoxycarbonyl)amino]-4-ethoxy-4-oxobut-2-enyl)prolinate [(E)- and (Z)-125] 16 ... 

The beryllium chelate of 2,4-pentanedione is another example of a stable chelate it melts at 108°, boils at 270°, and is soluble in many organic solvents. By replacing the methyl groups of 2,4-pentanedione with rert-butyl groups, a diketone is obtained which, with many metals including transition and rare-earth metals, forms complexes that often are highly soluble in nonpolar organic solvents. The interior of these chelates is saltlike but the exterior is hydrocarbonlike and nonpolar, which accounts for the substantial solubility in nonpolar solvents. 

LS S,3/ )-4-(rert-Butyldimethylsiloxy)-1-isopropyl-2-(methoxymethoxy)-3-methylbutyl (4R,5S)-4-(Benzyloxycarbonylammo)-5-methyl-3-oxoheptanoate (51H1251... 

The third step of this sequence, illustrated below, is an Sn2 reaction between a phenol anion and methyl iodide. The mechanism for an Sn2 reaction was presented in detail in Chapter 4. In this reaction it is important to use a base that is sufficient to deprotonate a phenolic hydroxyl group. Potassium rert-butoxide is generally sufficient to affect this deprotonation. 

Methyl ethers were applied firstly to the GC of cholesterols [390,391]. They are prepared by the method common for the preparation of ethers, e.g., by treatment with dimethyl sulphate or methyl iodide in the presence of potassium rert.-butoxide (cf., p. 64). Their good chromatographic properties, e.g., on SE-30 and PEGS stationary phases, are usually obtained only after further treatment with a silylating or acylating agent. 

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