Of 2.2-dimethyl

In Problem 5 17 (Section 5 13) we saw that acid catalyzed dehydration of 2 2 dimethyl cyclohexanol afforded 1 2 dimethylcyclohexene To explain this product we must wnte a mecha nism for the reaction in which a methyl shift transforms a secondary carbocation to a tertiary one Another product of the dehydration of 2 2 dimethylcyclohexanol is isopropyhdenecyclopentane Wnte a mechanism to rationalize its formation... 

Acid catalyzed dehydration of 2 2 dimethyl 1 hexanol gave a number of isomeric alkenes including 2 methyl 2 heptene as shown in the following formula... 

The reaction of 2 2 dimethyl 1 propanol with HBr is very slow and gives 2 bromo 2 methyl propane as the major product... 

Note 1). The mixture is heated with a mantle with stirring for 32 hr under a 50-cm fractionating column packed with 5-nm glass beads and topped by a Dean-Stark trap. The reaction mixture is then distilled through the packed column. The fraction which boils at 120 -126°C is collected. The yield is 86.0-87.3 g (77-78%) of 2,2-dimethyl-4-pentenal (1) as a clear, colorless oil, n 1.4216 (Note 2). 

The Roussel group has described recently a novel method for the synthesis of 2,2-dimethyl-A" -3-keto steroids. Thus addition of potassium t-butoxide to a solution of 19-nortestosterone (25) in tetrahydrofuran containing methyl iodide and hexamethylphosphorous triamide at —70° affords the 2,2-dimethyl compound (26) in good yield.Methylation of A" -3-ketone by the classical conditions, namely addition of methyl iodide to a solution of the steroid and potassium /-butoxide, leads to the 4,4-dimethyl product. 

A solution of 0.7 g (18 mmoles) of potassium in 35 ml of /-butanol is added to a boiling solution of 5 g (13 mmoles) of 5a-cholestan-3-one in 50 ml of benzene and 25 ml of /-butanol. A total of 5 ml (11.4 g, 80 mmoles) of methyl iodide in 50 ml of benzene is then added and refluxing is continued for 3 min. The solution is cooled, ice is added and the product is isolated by extraction with ether. The crystalline residue in light petroleum solution is chromatographed on 300 g of alumina. Elution with light petroleum yields initially 0.55 g (10%) of 2,2-dimethyl-5a-cholestan-3-one mp 111-113° [o(]d 77° (CHCI3), after crystallization from ether-methanol. Further elution affords 1.01 g (20%) of 2a-methyl-5a-cholestan-3-one mp 119-120° [a]o 32° (CHCI3), after crystallization from ether-methanol. 

The product, isolated as above, is dissolved in pentane solution and chromatographed on 100 g of alumina. The initial fraction eluted with pentane, yields 1.02 g (48%) of 2,2-dimethyl-5a-cholestan-3-one mp 111-113°, after crystallization from ether-methanol. The subsequent fraction, eluted with pentane and pentane-benzene (9 1) gives 0.12 g (6%) of 2a-methyl-5a-cholestan-3-one mp 119-120°, after crystallization from methanol-ether. 

The alkene mixture obtained on dehydration of 2,2-dimethyl-cyclohexanol contains appreciable amounts of 1,2-dimethylcyclohexene. Give a mechanistic explanation for the formation of this product. 

Step G 4-fOrtho-(2, 3 -Dihydroxypropyloxycarbonyl)-Phenyl]-Amino-8-Trifluoromethyl-quinoHne Acetonide — 100 cc of toluene were added to 80 cc of 2,2-dimethyl-4-hydroxy-methyl-1,3-dioxolane and the toluene was distilled off under reduced pressure to eliminate the water present. To the anhydrous 2,2-dimethyl-4-hydroxymethyl-1,3-dioxolane thus obtained, 0.25 gram of an oily 50% suspension of sodium hydride and then 21.3 grams of 4-... 

The aldol reaction of 2,2-dimethyl-3-pentanone, which is mediated by chiral lithium amide bases, is another route for the formation of nonracemic aldols. Indeed, (lS,2S)-l-hydroxy-2,4,4-trimethyl-l-phenyl-3-pentanone (21) is obtained in 68% ee, if the chiral lithiated amide (/ )-A-isopropyl-n-lithio-2-methoxy-l-phenylethanamine is used in order to chelate the (Z)-lithium cnolate, and which thus promotes the addition to benzaldehyde in an enantioselective manner. No anti-adduct is formed25. 

Several authors studied the influence of substituents on activation parameters. Bad-dar et al.315 who studied the polyesterification of y-arylitaconic anhydrides and adds with 1,2-ethanediol found that in the non-catalyzed reaction a p-methoxy substituent decreases both the activation enthalpy and the entropy whereas an increase is observed with a p-chloro substituent. On the other hand, Huang et al., who studied the esterification of 2,2-dimethyl-l,3-propanediol with benzoic, butanedioic, hexanedioic, decanedioic and o-phthalic add found the same values since the activation enthalpy is 64 kJ mol-1 for the first reaction and 61 kJ mol-1 for the others. 

The lithio-derivative derived from cyclohexyl phenyl sulfone underwent 1,2-addition to cyclohexenylideneacetaldehyde or cinnamaldehyde to give the corresponding / -hydroxysulfones387. Reactions of 2,2-dimethyl-4-lithio-1,3-oxathiane 3,3-dioxide 308... 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

Recently Mosher and Driscoll 2 have noted that the polymerization of acrylonitrile can be observed during the chromic acid oxidation of 2,2-dimethyl-l-phenyl-l-propanol. The polymerization is caused by radicals formed during the oxidation of benzaldehyde (which is one of the cleavage product of phenyl-1-butylcarbinol). The oxidation of benzaldehyde is due to the chromium(IV), most probably, or chromiun(V) intermediates. 

An intramolecular Michael type reaction of a nitrogen nucleophile to nitroalkene, as shown in Eq. 4.31, provides a useful method for the preparation of 2,2-dimethyl-l-carbapenam.37... 

Steric factors were found to make a considerable contribution to the stability of these adducts. Thus, increasing the number of alkyl substituents in the 2-position of either of the two heteroadamantane frameworks leads to a weakening of the B-N coordination bond as a result of steric repulsion. That is why the adduct of 2,2-dimethyl-l-boraadamantane with its azaanalogue easily dissociates into the parent compounds rendering isolation of this compound impossible <1998IZV1818>. 

Homochiral pyridyl, bipyridyl, and phosphino derivatives of 2,2-dimethyl-1,3-dioxolane (113)-(115) were prepared from T-(+)-tartrate. These compounds were assessed in metal-catalyzed asymmetric hydroformylation of styrene enantioselectivity was generally low.342... 

Metcalf, R.L., T.R. Fukuto, C. Collins, K. Borck, S.A. El-Aziz, R. Munoz, and C.C. Cassil. 1968. Metabolism of 2,2-dimethyl-2,3-dihydrobenzofuranyl-7-A-methylcarbamate (Furadan) in plants, insects, and mammals. Jour. Agric. Food Chem. 16 300-311. 

Gas chromatographic analysis at 155° on a 5 ft. 5% SE-30 column shows only the presence of 2,2-dimethyl-3-phenylpropanal and solvent. 

FIGURE 8.9 Synthesis of 2,2-dimethyl-l,3-oxazolidines by reaction of the Fmoc-dipeptide with 2,2-dimethoxypropane (A) giving Fmoc-Xaa-Ser((4 MeMepro)-OH and (B) giving Fmoc-Xaa-Thr(4 MeMepro)-OH. Synthesis of a 2-methyl-1,3-thiazolidine by acylation of the cyclic parent (C) giving Fmoc-Xaa-Cys(YHMepro)-OH. NCA = /V-carboxyanhydridc. 

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