Alcohols, reaction with carbonyls

Reaction With Carbonyl Compounds. Primary and secondary nitroparaffins undergo aldol-type reactions with a variety of aldehydes and ketones to give nitro alcohols (11). Those derived from the lower nitroparaffins and formaldehyde are available commercially (see Nitro alcohols). Nitro alcohols can be reduced to the corresponding amino alcohols (see Alkanolamines). 

Allylboron compounds have proven to be an exceedingly useful class of allylmetal reagents for the stereoselective synthesis of homoallylic alcohols via reactions with carbonyl compounds, especially aldehydes1. The reactions of allylboron compounds and aldehydes proceed by way of cyclic transition states with predictable transmission of olefinic stereochemistry to anti (from L-alkene precursors) or syn (from Z-alkene precursors) relationships about the newly formed carbon-carbon bond. This stereochemical feature, classified as simple diastereoselection, is general for Type I allylorganometallicslb. 

For primary alkyl phenyl ethers 47, their hthiation under catalytic conditions (DTBB, 5%) in THF at room temperature gave the expected alkyUithiums, which by reaction with carbonyl compounds afforded, after hydrolysis, the expected alcohols 48 (Scheme 15) . In this case, only the O—Caiiyi bond cleavage was observed . On the other hand, the reaction shown in Scheme 15 failed for secondary (R = i-Pr) or tertiary (R = f-Bu) starting materials. 

Cleavage of the S-C(2) bond occurs when thiochroman is treated with the radical anion 4,4 -di-/-butylbiphenylide (LDBB). The resulting ring-opened dianion 317 has good synthetric potential. For example, the alcohols arising from reaction with carbonyl compounds can be cyclized under acidic conditions to benzothiepines (Scheme 56) < 1995TL4459>. 

The reaction of allylindium sesquibromide with 4 equiv. of bulky lithium alkoxide results in modified reagents 7, which show unusual degrees of chemo- and diastereoselectivity in the reactions with carbonyl compounds for example, allylation of 2-methylcyclohexanone gives a high ratio of axial alcohol 8/equatorial alcohol 9 (Scheme 15).128... 

Reaction with carbonyl compounds (e.g., <2004JHC443>) or epoxides (e.g. <2002JOC9354>) to form alcohols, thus 2-picoline 649 the tertiary alcohol 654. 

The above transformation has two different goals 21,22) 1) To increase chemo-, regio-, diastereo- and enantioselectivity in the reaction with carbonyl compounds (Sections C-E), and 2) to make certain reaction types amenable which do proceed readily with classical reagents, e.g., methylation of tertiary alkyl halides, alcohols and ethers, and direct geminal dialkylation of ketones (Section F). It turns out that organotitanium compounds are usually complementary to Li, Mg, Zn, Fe, Ni, Cu and Pd reagents. So far, experience in the above two areas points to the following positive aspects ... 

The base-catalyzed reaction in Equations (2a) and (2b) is very similar to the corresponding alcohol reaction with this difference. Since the mer-captide ion is more nucleophilic than the alkoxide ion one will expect that smaller differences in the charge density around the carbonyl carbon of the isocyanate will affect the reactivity of the mercaptides than that of the alkoxides. This would explain the higher sensitivity of thiols to base-catalysis and the higher activity of bases for the catalysis of the thiol reaction. 

Unusual carbanions. Lithium homoenolates are formed from P-aryl-a,P-unsaturated ketones and esters. Their reaction with carbonyl compounds leads to y-lactols and lactones. Reductive dechlorination of a-chloroimines provides a-amino carbanions. Access to 1,2-amino alcohols is assured. 

The preparation of allyltitanium compounds including those having functional groups is described by reaction of allylic halides or allylic alcohol derivatives with the system Ti(OPr1)4/MgXPr1 (X = C1, Br) (Scheme 7).24 Analogous allyltitanium complexes have also been reported by treatment of Ti(n) species with allylic alcohol derivatives, which proceeds via an oxidative addition pathway. Their reactions have been studied.25-27 These compounds are used to promote efficient syntheses of alkylidenecyclopropane and cycloalkane derivatives by regioselective reactions with carbonyl compounds,28,29 the stereoselective syntheses of optically active substituted piperidines and pyrrolidines... 

Allenyltitanium systems are formed from propargyl halides or carbonates and a low-valent diisopropoxo-772-propene Ti(n) species. They are excellent reagents for the synthesis of homopropargyl alcohols by reaction with carbonyl compounds, as examples of carbon-carbon bond-forming processes.36,37... 

Alcohols react with carbonyl difluoride in a similar way to that described for phosgene (see Section 10.3.1). The first stage of the reaction is the formation of the fluoroformate. 

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