Dimerization carbinols

Reduction of 1-ethoxycarbonyl-l/f-azepine with lithium aluminum hydride in ether at -15 °C yields the thermally unstable 1-(hydroxymethyl) derivative in boiling ether further reduction occurs to N-methyl- lH-azepine, which subsequently dimerizes to the [6+6]ir adduct (see Section 5.16.3.2.3) (B-69MI51600). Surprisingly, the action of phenyllithium on 1 -ethoxycarbonyl-l//-azepine produced the carbinol (2 R CPlhOH, R2 = H), thermal decomposition of which led to the first characterization of 3//-azepine (73CB1033). 

Consequently we next searched for a molecule sufficiently hindered to prevent polymer formation but readily able to form dimer. Such a molecule is methyl ethyl tertiary butyl carbinol. The infrared spectrum makes it clear that this molecule forms only dimer. A comparison of the equilibrium constant for this substance with that for the... 

On the other hand, treatment of 30 with LDA, followed by oxidation, results in the formation of dimer 32 (Scheme 10) (79JOC2081). That this reaction proceeds via 31 by initial ortho metalation was established by performing the reaction between -65 and -10°C in the presence of ben-zaldehyde, which led to the formation of the carbinol 33. 

Products of the type (24) also result from enolizable ketones without the formation of silyl enol ethers if the reaction is carried out in the presence of tertiary phosphines. The proposed mechanism involves the betaine R3P—SiMe2 as the silylene transfer agent. In preventing a 1,3-hydrogen migration, the phosphine may well induce dimerization prior to oxasilacyclopropane formation. The dioxadisilacyclohexane (24) can be reduced with LiAIHU to give dimethylsilyl-substituted carbinols, so the reaction is of synthetic value (Scheme 34) (78JA7074). 

The so-called 2,2-diphenylchromene dimer (again the name is misleading) is obtained in the reaction of coumarin with CeHgMgBr, or from the carhinol (62, R = Ph). In this case the mechanism that requires the dehydration of the carbinol is not possible, and structure (66) has been proposed on the basis of the NMR spectrum.262 This... 

Aldehydes can be reduced in a one-electron step to give a dimeric product, or pinacol (Scheme 14). The radical anion monomer yields the carbinol, which can be further reduced to the hydrocarbon (see Section II,D). Control of the experimental conditions allows one to achieve selectivity, and the major product can be any one of these three possibilities. 

The larger part of the work on ketones concerns the reduction of the isomeric acetylpyridines (48). The products were the carbinols (49) and pina-cols (50) (Scheme 17) there are no reports of alkylpyridine products, as were seen in carbinol reductions (see Section II,D). In acidic media, reduction of 2-(48) gave almost exclusively 2-(49) and little dimer.69 What dimer was formed was mostly meso and the proportion of it increased as pH increased. 

Increasing junction potential also increased carbinol yield as was seen with aldehyde reductions. In basic electrolytes or in nonaqueous media, the dimer 50 was the major product. 

Production of pinacols (50) in preference to carbinols (49) has also received interest. All three isomers of 48 were studied by Allen and Cohen and found to give the respective dimer 50 in good yield.77 Reduction of 3-(48) to give 3,3 -(50) was examined further and the rearrangement to the pinacolone analog was done.78... 

N-Methylaniline adds to cyclopropanone to give the expected carbinol amine in quantitative yield. 5-90> On the other hand, a mixture of addition products may be isolated from the reaction of cyclopropanone 5>90> or cyclopropanone ethyl hemiketal4) with aniline (Scheme 18). At — 78°C, the carbinol amine 104 (66%) and the dimeric species 105 (33%) were obtained when the reactants were present in stoichiometric amounts. With excess aniline, 104 was produced almost quantitatively. However, at 25 °C, both 104 and the dianilino product 106 were obtained. These products could be interconverted by the addition of aniline or cyclopropanone, respectively. At 125 °C, o-propionylaminopropiophenone (107) was formed, possibly by further reaction of the carbinol amine with cyclopropanone as shown. 4>... 

FEMA No. 2008 Acetyl Methyl Carbinol Dimethylketol 3-Hydroxy-2-butanone Dimer 176.21/C8H1604/ H3C CH3 HO-C-C-OH HO-C-C-OH h3c ch3 Dimer white to pale yel powder/ odorless 148° Dimer s—hot prop glycol ins—most solvents ss—weak alkali ... 

Ferrocenylcarbinols undergo transformations in strong acid media which are believed to involve an internal oxidation-reduction step. These processes were first observed in the attempted hydroxyalkylation reactions of ferrocene with benzaldehyde or formaldehyde in the presence of sulfuric acid 33, 34, 4, The product was not the anticipated carbinol but the dimeric substances (I a,b). Their origin has been accounted for... 

In addition to the anticancer indole alkaloids vinblastine and vincristine, discnssed in the next section, many indoles display antitumor activity. Space does not allow complete coverage of these smdies. Indole-3-carbinol (Scheme 12, 75), found in vegetables of genns Brassica (kale, cauliflower, broccoli, turnip, collard, and others), its acid- and/or enzymatic-induced dimer, 3,3 -diindolylmethane (76), and its trimer, 2-(indol-3-yhnethyl)-3,3 -diindolylmethane (77), inhibit cancer cell proliferation and induce apoptosis in several cell lines [88-91]. However, one study reports that... 

Carboxyl End Groups. Termination of bifimctional living polystyrene by solid CO2 yields polymers with carboxyl end groups (169). Because of its commercial potential, this reaction has been studied in depth. In addition to carboxyl groups (60%), dimeric ketones (30%) and trimeric carbinols (10%) are formed with gaseous CO2 (170). 

A few organotitanium alkoxides have been structurally determined. In bis-benzyl titanium diethoxide a centrosymmetric dimer [(C6H5CH2)4Ti2(/r-OEt)2(OEt)2] is formed involving five-coordinated Ti in a distorted TBP configuration. In bis-methyl titanium tritox methoxide (tritox = tri-tert-butyl carbinolate, BU3CO) the methoxo... 

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