Molecule, acetone benzaldehyde

The aldol condensation of 2-propanone (acetone) with two molecules of benzaldehyde forms the product shown. Explain the stereochemistry of the carbon-carbon double bonds in the product. 

When acetone is treated with excess benzaldehyde in the presence of base, the crossed condensation adds two equivalents of benzaldehyde and expels two equivalents of water. Propose a structure for the condensation product of acetone with two molecules of benzaldehyde. 

The crossed condensation of an aromatic aldehyde with a ketone usually gives a high yield of the unsaturated ketone directly. Acetone is condensed with either one or two molecules of benzaldehyde to give ben-zalacetone (68%) or dibenzalacetone (94%), respectively. Alkyl stytyl ketones, CjHs CH = C(R)COR, have been prepared from benzalde-hyde and higher ketones in the presence of hydrochloric acid or alkali hydroxide. Substituents on the phenyl group include methyl, hydroxyl, methoxyl, and nitro groups. A survey of condensa-... 

Formed by the aldol condensation of acetone with two molecules of benzaldehyde. 

The ion (97), acting as an electrophilic reagent, can also attack another molecule of the heterocyclic compound. Thiophene with benzaldehyde or chloral gives the dinuclear product (100 R = Ph, CC13). Pyrrole and furan react with acetone to form tetranuclear derivatives of type (101 Z = NH, O). Pyrroles with a single free position react analogously to thiophene e.g. two molecules of 3-ethoxycarbonyl-2,4-dimethylpyrrole with formaldehyde afford the dipyrromethane (102). 

The product has 17 carbons, which suggests that it is formed from two benzaldehyde molecules (2x7 = 14 carbons) + one acetone molecule (3 carbons). The product forms by a double mixed aldol condensation ... 

Cesium-exchanged zeolite X was used as a solid base catalyst in the Knoevenagel condensation of benzaldehyde or benzyl acetone with ethyl cyanoacetate [121]. The latter reaction is a key step in the synthesis of the fragrance molecule, citronitrile (see Fig. 2.37). However, reactivities were substantially lower than those observed with the more strongly basic hydrotalcite (see earlier). Similarly, Na-Y and Na-Beta catalyzed a variety of Michael additions [122] and K-Y and Cs-X were effective catalysts for the methylation of aniline and phenylaceto-nitrile with dimethyl carbonate or methanol, respectively (Fig. 2.37) [123]. These procedures constitute interesting green alternatives to classical alkylations using methyl halides or dimethyl sulfate in the presence of stoichiometric quantities of conventional bases such as caustic soda. 

As to be expected, the restricted NRG is seen to be isomorphic to the full NRG, and the external symmetry rotation group is found to be isomorphic to the symmetry point group of the molecule, C, in its most synunetric configuration. Similar expressions may be deduced for benzaldehyde, pyrocatechin and acetone. 

In the present paper, symmetry eigenvectors which factorize the Hamiltonian matrix into boxes are given for the single rotation in phenol (24) for double rotations in benzaldehyde (29), pyrocatechin (34) and acetone (44-46), for double rotation and inversion in non-planar pyrocatechin (40) and pyramidal acetone (49-51). In the same way, symmetry eigenvectors deduced in the local approach are deduced for some of these non-rigid systems (79), (83), and (89). Symmetry eigenvectors for the double internal Czv rotation in molecules with frame of any symmetry are given in reference [36]. 

Acetophenone, benzophenone and benzaldehyde absorb at higher wavelengths (325, 348 and 328 m/x respectively) compared to acetone (277 m/x). This is due to conjugation in these molecules. The n->7T bands in these systems arfe seen immediately next to the very intense 7r-> tt bands, and often the former bands completely merge into the latter in polar solvents. 

Simple aldehydes and ketones have common names that are so well known they cannot be ignored. Three simple aldehydes are formaldehyde, acetaldehyde, and, when the aldehyde unit is attached to a benzene ring, the molecule is known as benzaldehyde. The simplest ketone is acetone, but other common ketones are benzophenone and pinacolone. The lUPAC system will be described and these names will be given their proper name at that time. However, the common names are used extensively and they must be learned. 

The self-condensation of butanal involves a single compound, but it is also possible to convert one ketone or aldehyde to an enolate anion, and it wiU react with a different ketone or aldehyde. This is called a mixed aldol condensation. If acetone (2) is treated with aqueous NaOH in the presence of another carbonyl molecule, such as benzaldehyde (25), enolate (26) is formed in situ. This enolate anion may react with itself (with another molecule of 2 in a selfcondensation reaction), but it may also react with aldehyde 25 via acyl addition to give alkoxide 28. Mild hydrolysis gives the mixed aldol product, 26. There is a competition for the reaction of 27 with either 2 or 25, so at least two products are possible in the reaction 28 and the self-condensation product. Note... 

There are subtle reactivity differences between dioxanes and dioxolanes that may be exploited in complex molecule synthesis. This can be of considerable use in the selective removal of these acetal protecting groups under oxidative conditions. A classic example is to be found in Stork s innovative synthesis of erythronolide A (Scheme 6.11) (36). Selective oxidation of 56 with ozone leads to cleavage of the dioxolane in preference to the dioxane to furnish 57. The selectivity is associated with the stereoelectronic effects (LPo<- C-H) that render the dioxolane C-H more labile. The structural differences between dioxolanes and dioxanes can also be used to gain access to protected butane-1,2,4-triol derivatives, as shown on the right [7, 9]. Thus, either 1,2- or 1,3-diols can be selectively masked as the corresponding dioxolane or dioxane, respectively, by selection of acetone or benzaldehyde as the reacting partner. 

Asymmetric catalysis is an important technique for the synthesis of chiral compounds. The introduction of supported IL catalyst into the field of asymmetric catalysis might offer new approaches to improve the catalytic performance and also the reusabiUty of chiral catalysts. The first example of a supported IL asymmetric catalyst is the proUne-catalyzed aldol reaction [116]. In this work, the IL molecule covalently attached to modified silica gel was used as the support for IL-phase containing L-proUne. The modification of the silica gel surface by the IL molecule is crucial to gain high enantioselectivity. In the model reaction of acetone and benzaldehyde, the yield to 4-hydroxy-4-phenylbutan-2-one was 51% with 64% ee. Otherwise, the yield was only 38% with 12% ee without the silica gel modification. 

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