Ketones functional heteroatom groups

Tab. 6.2. Syntheses of alkenes by intermolecular McMur reactions of aldehydes and ketones with functional heteroatom groups.

Most of the compounds that you have encountered in this text so far have been fairly simple. In addition to any carbon-carbon double or triple bonds, they have contained only one functional group and could be named by using suffixes such as -ynol or -dienone. However, for a compound that contains more than one heteroatom functional group, only one of these functional groups can be designated in the suffix. For example, consider the following compound, which has both alcohol and ketone functional groups ... 

Heteroatom groups such as boron or silicon can activate or direct synthetic reactions. Use of such activation has become of major importance in organic syntheses. Examples in this volume are BORANES IN FUNCTIONALIZATION OF DIENES TO CYCLIC KETONES BICYCLO[3.3.1]NONAN-9-ONE and BORANES IN FUNCTIONALIZATION OF OLEFINS TO AMINES 3-PINANAMINE. Use of trimethylsilyl or trimethyl-silyloxy groups to activate a 2-butenone or a butadiene are illustrated by the preparations 3-TRIMETHYLSILYL-3-BUTEN-... 

In the case of esters, carboxylate anions, amides, and acid chlorides, the tetrahedral adduct may undergo elimination. The elimination forms a ketone, permitting a second addition step to occur. The rate at which breakdown of the tetrahedral adduct occurs is a function of the reactivity of the heteroatom substituent as a leaving group. The order of stability of the... 

Reactions in chloroaluminate(III) salts and other related binary salts often proceed smoothly to give products. However, it should be noted that these salts are water-sensitive and must be handled under dry conditions. They react with water to give hydrated aluminium(III) ionic species and HCl. When a reactant or product contains a heteroatomic functional group, such as a ketone, a strong ketone/alumini-um(III) chloride adduct is formed. In these cases, this adduct can be difficult to separate from the ionic liquid at the end of a reaction. The isolation of the product often... 

Other functional groups which have a heteroatom rather than a hydroxyl group capable of directing the hydrogenation include alkoxyl, alkoxycarbonyl, carboxylate, amide, carbamate, and sulfoxide. The alkoxy unit efficiently coordinates to cationic iridium or rhodium complexes, and high diastereoselectivity is induced in the reactions of cyclic substrates (Table 21.3, entries 11-13) [25, 28]. An acetal affords much lower selectivity than the corresponding unsaturated ketone (Table 21.3, entries 14 and 15) [25]. 

The enantioselective hydrogenation of ketones which have two heteroatoms on both sides of the carbonyl group tends to give lower enantioselectivity due to the competitive interaction of the functionalities with the catalyst. The extent depends... 

Of course, a-cleavage can also occur in alicyclic ketones and other heteroatom-substituted alicyclic compounds. However, a single bond cleavage cannot release a neutral fragment, because this is still adhering to another valence of the functional group ... 

The conjugate addition of heteronucleophiles to activated alkenes has been used very often in organic synthesis to prepare compounds with heteroatoms [3 to various activating functional groups, e.g. ketones, esters, nitriles, sulfones, sulfoxides and nitro groups. As in the Michael reaction, a catalytic amount of a weak base is usually used in these reactions (with amines as nucleophiles, no additional base is added). 

Highly enantioselective hydrogenation of functionalized ketones has been achieved with chiral phosphine-Rh(I) and -Ru(II) complexes [1,162], The presence of a functional group close to the carbonyl moiety efficiently accelerates the reaction and also controls the stereochemical outcome. The heteroatom-metal interaction is supposed to effectively stabilize one of the diastereomeric-transition states and/or key intermediates in the hydrogenation. 

The above mechanism is novel in that it does not require the interaction of a carbonyl moiety with the metal center. Neither a ketone/Ru complex nor a Ru alkoxide is involved in the mechanism, and the alcohol forms directly from the ketone. This non-classical mechanism also explains the high functional selectivity for the C=0 group. When the chiral molecular surface of the Ru hydride recognizes the difference of ketone enantiofaces, asymmetric hydrogenation is achieved. This is different from the earlier BINAP Ru chemistry where the enantio-face differentiation is made within the chiral metal template with the assistance of heteroatom/metal coordination. Similar heterolyses of H2 ligands have been shown by Morris and others (92) to be the critical step in the mechanism of reaction processes related to the Noyori systems. 

Assigning the peaks to individual carbons in a C SSNMR experiment is not always trivial, as peaks can vary by more than 10 ppm from their solution values. In a broad sense, peaks from 160 to 180 ppm are due to carbonyl groups of carboxylic acid derivatives, 200-220 ppm are due to ketone carbonyls, 100-160 ppm are from aromatic and olefinic carbons, 50-100 ppm are from sp -hydridized carbons attached to heteroatoms, and 10-40 ppm are typically aliphatic carbons attached to other carbons and/or hydrogens. These are purely estimates of the basic functionalities found in most organic molecules, and exceptions to these ranges are not uncommon. Many crystalline systems also possess more than one crystallographically inequivalent molecule per unit cell, which is also easily detectable in SSNMR experiments and can make interpretation of spectra more complicated. For instance, if two peaks exist in the C SSNMR spectrum for each carbon, there are two molecules in the unit cell, although not every peak in each inequivalent molecule is always resolved. 

Despite the fact that polar entities are catalyst poisons, a variety of acyclic olefins containing a heteroatom functional group can undergo metathesis in the presence of a suitable catalyst, although at a high catalyst level. These include unsaturated esters, ethers, ketones, amines, nitriles, halogens, etc. [14]. In particular metathesis reactions - including ethenolysis - of unsaturated fatty esters and fatty oils are of interest, as they have perspectives for the oleochemical industry [15]. 

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