Carbonyl compounds, addition reactions alcohols

Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol if it is an imine, identify the carbonyl compound and the amine and so forth. 

Trialkyl phosphites readily undergo conjugate addition with a,(3-unsaturated carbonyl compounds in the presence of a proton source, such as a protic solvent.359 The use of a protic solvent, such as an alcohol, obviates the difficulties found in the performance of the simple Abramov-type reaction with a,(3-unsaturated carbonyl compounds.189198 In alcohol medium, an ether is generated as a by-product in the dealkylation process (Equation 3.22). 

Wu et alP have synthesized a TSIL having 2,2,6,6-tetramethylpiper-idine-l-oxyl (TEMPO) appended to an imidazolium cation for the oxidation of alcohols to corresponding carbonyl compounds. These reactions have shown high yields similar to non-supported TEMPO, but with the additional advantage of easy separation of products. 

The addition of a hydride donor to an aldehyde or to a ketone gives an alcohol. This addition is therefore also a redox reaction, namely, the reduction of a carbonyl compound to an alcohol. Nevertheless, this type of reaction is discussed here and not in the redox chapter (Chapter 17). 

Exchange of the zirconium for zinc allows addition to carbonyl compounds. A free alcohol group, as in 130, must be protected and the zirconium in the initial product 132 replaced by zinc before the aldehyde is added to give the allylic alcohol 134. Both reactions occur with retention of configuration.29... 

House pointed out that 16 can disproportionate (as mentioned above) or that another mechanism may be operative in this reduction.24 Inverse addition of the hydride (a slurry of LiAlH4 is added to the carbonyl compound), short reaction times, and low reaction temperatures generally give moderate to good yields of the conjugate reduction product.24 Good yields of allylic alcohols can often be obtained from a,P-unsaturated aldehydes, however, when the reaction is done at low temperatures with strict control of the stoichiometry. 

We now come to the primary value of tlic.se reagents their ability to react as. nucleophiles toward the electrophilic carbon in carbonyl compounds ( C = 0). In a reaction mechanistically analogous to the hydride additions of Section 8-6. orgaiiomelallic reagents add nucleophilic carbon to aldehydes and kcioncs. rcsulliiig in alcohols, and making a new carbon-carbon bond in the process. Ai die end of the next seciion, you will find a summary chart of the major types of reactions that convert carbonyl compound.s to alcohols. 

An alternative method for the formation of aldehydes or ketones makes use of the complexes formed from a methyl sulfide with chlorine or A-chlorosuccinimide (NCS), in what is called the Corey-Kim oxidation. With dimethyl sulfide the salt 28 is generated and reacts with the alcohol to give the alkoxysulfonium salts and hence, on treatment with a base, the carbonyl compound. This reaction has fovmd particular application in the oxidation of 1,2-diols in which one alcohol is tertiary, to give a-hydroxy-aldehydes or ketones without rupture of the carbon-carbon bond. For example, the aldehyde 32 is formed in good yield from the diol 31 using dimethyl sulfide and NCS followed by addition of triethylamine (6.29). This transformation is thought to depend on the preferential five-membered transition... 

Traditionally, it is the addition of organomagnesium compounds (Grignard reagents) to carbonyl compounds to generate alcohols. A more modern interpretation extends the scope of the reaction to include the addition of Grignard reagents to a wide variety of electrophilic substrates ... 

Alcohols can be synthesized by the addition of carbanions to carbonyl compounds (W.C. Still, 1976) or epoxides. Both types of reactions often produce chiral centres, and stereoselectivity is an important aspect of these reactions. 

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Cellobiose was prepared first by Skraup and Konig by the saponification of the octaacetate with alcoholic potassium hydroxide, and the method was improved by Pringsheim and Merkatz.3 Aqueous barium hydroxide also has been employed for the purpose, and methyl alcoholic ammonia has been used extensively for the hydrolysis of carbohydrate acetates. The method of catalytic hydrolysis with a small quantity of sodium methylate was introduced by Zemplen,i who considered the action to be due to the addition of the reagent to the ester-carbonyl groups of the sugar acetate and the decomposition of the addition compound by reaction with alcohol. The present procedure, reported by Zemplen, Gerecs, and Hadacsy, is a considerable improvement over the original method (see Note 2). 

---