Organic chemistry compounds with carbonyl

We have now completed our survey of the basic organic chemistry compound classes, as defined by simple functional groups. In the remainder of the book, we shall examine compounds with multiple functional groups, whether they be the same or different. We shall see the amino group and amine derivatives again in these chapters, particularly when studying heterocycles, proteins, and nucleic acids. We shall learn that the combination of the amino and carbonyl groups underlies the molecular structure of life itself. 

The [ 2 + 4]-cycloaddition reaction of aldehydes and ketones with 1,3-dienes is a well-established synthetic procedure for the preparation of dihydropyrans which are attractive substrates for the synthesis of carbohydrates and other natural products [2]. Carbonyl compounds are usually of limited reactivity in cycloaddition reactions with dienes, because only electron-deficient carbonyl groups, as in glyoxy-lates, chloral, ketomalonate, 1,2,3-triketones, and related compounds, react with dienes which have electron-donating groups. The use of Lewis acids as catalysts for cycloaddition reactions of carbonyl compounds has, however, led to a new era for this class of reactions in synthetic organic chemistry. In particular, the application of chiral Lewis acid catalysts has provided new opportunities for enantioselec-tive cycloadditions of carbonyl compounds. 

Alcohols are among the most versatile of all organic compounds. They occur widely in nature, are important industrial 7, and have an unusually rich chemistry. The most widely used methods of alcohol synthesis start with carbonyl compounds. Aldehydes, ketones, esters, and carboxylic acids are reduced by reaction with LiAlH4. Aldehydes, esters, and carboxylic acids yield primary alcohols (RCH2OH) on reduction ketones yield secondary alcohols (R2CHOH). 

Whereas the original Moffat-Pfitzner oxidation employs dicyclohexylcarbodiimide to convert DMSO into the reactive intermediate DMSO species 1297, which oxidizes primary or secondary alcohols via 1298 and 1299 to the carbonyl compounds and dicyclohexylurea [78-80], subsequent versions of the Moffat-Pfitzner oxidation used other reagents such as S03/pyridine [80a, 83] or oxalyl chloride [81-83] to avoid the formation of dicyclohexylurea, which is often difficult to remove. The so-called Swern oxidation, a version of the Moffat-Pfitzner oxidation employing DMSO/oxalyl chloride at -60°C in CH2CI2 and generating Me2SCl2 1277 with formation of CO/CO2, has become a standard reaction in preparative organic chemistry (Scheme 8.31). 

Carbonyl reactions are extremely important in chemistry and biochemistry, yet they are often given short shrift in textbooks on physical organic chemistry, partly because the subject was historically developed by the study of nucleophilic substitution at saturated carbon, and partly because carbonyl reactions are often more difhcult to study. They are generally reversible under usual conditions and involve complicated multistep mechanisms and general acid/base catalysis. In thinking about carbonyl reactions, 1 find it helpful to consider the carbonyl group as a (very) stabilized carbenium ion, with an O substituent. Then one can immediately draw on everything one has learned about carbenium ion reactivity and see that the reactivity order for carbonyl compounds ... 

The reported structural chemistry of zinc aldehyde complexes is dominated by Vahrenkamp and co-workers. A systematic investigation is reported over three papers published in 1999. All X-ray structures reported in these papers are aryl aldehydes and no aliphatic aldehyde structures with zinc were found in the CSD. Zinc is frequently exploited in preparative organic chemistry and enzyme-catalyzed transformations of organic carbonyl compounds. 

The base-catalysed addition of thiols to Jt-electron-deficient alkenes is an important aspect of synthetic organic chemistry. Particular use of Triton-B, in place of inorganic bases, has been made in the reaction of both aryl and alkyl thiols with 1-acyloxy-l-cyanoethene, which behaves as a formyl anion equivalent in the reaction [1], Tetra-n-butylammonium and benzyltriethylammonium fluoride also catalyse the Michael-type addition of thiols to a,P-unsaturated carbonyl compounds [2], The reaction is usually conducted under homogeneous conditions in telrahydrofuran, 1,2-dimethoxyethane, acetone, or acetonitrile, to produce the thioethers in almost quantitative yields (Table 4.22). Use has also been made of polymer-supported qua-... 

Enzymes are natural biocatalysts that are becoming increasingly popular tools in synthetic organic chemistry [1]. The major areas of exploration have involved the use of hydrolases, particularly esterases and lipases [2]. These enzymes are readily available, robust and inexpensive. The second most popular area of investigation has been the reduction of carbonyl compounds to chiral secondary alcohols using either dehydrogenases (with co-factors) or a whole-cell system such as bakers yeast [3]. 

For reviews of thiokelones and other compounds with C=S bonds, see Schaumann, in Patai Supplement A The Chemistry of Double-bonded Functional Groups, vol. 2, pt. 2 Wiley New York. 1989. pp. 1269-1367 Ohno. in Oae Organic Chemistry of Sulfur, Plenum New York, 1977. pp. 189-229 Mayer, in Janssen Organosulfur Chemistry Wiley New York, 1967, pp. 219-240 Campaigne, in Palai The Chemistry of the Carbonyl Group, pt. 1 Wiley New York, 1966, pp. 917-959. 

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