2- Pentanone aliphatic aldehydes

A wide range of donor ketones, including acetone, butanone, 2-pentanone, cyclopentanone, cyclohexanone, hydroxyacetone, and fluoroacetone with an equally wide range of acceptor aromatic and aliphatic aldehydes were shown to serve as substrates for the antibody-catalyzed aldol addition reactions (Chart 2, Table 8B2.6). It is interesting to note that the aldol addition reactions of functionalized ketones such as hydroxyacetone occurs regioselectively at the site of functionaliztion to give a-substitutcd-fi-hydroxy ketones. The nature of the electrophilic and nucleophilic substrates utilized in this process as well as the reaction conditions complement those that are used in transition-metal and enzymatic catalysis. 

Pentanone is similar to acetone in its behavior, and 1 1 adducts may be obtained from aliphatic aldehydes in good yield (equations 47 and 48). 4-Heptanone and higher symmetrical ketones are much less reactive and give very poor yields of aldols with simple aldehydes. However, the reactions of these ketones with o-phthalaldehyde often provide benzotropone derivatives in excellent yield (e.g. equation 49). Diisopropyl ketone and diisobutyl ketone do not give mixed adducts with aldehydes under tte normal protic conditions. 

Dubois and Fellmann have studied the kinetic regioselectivity in the base-promoted reactions of 2-bu-tanone and 2-pentanone with a series of aliphatic aldehydes (equation 52) results are summarized in Table 2. The data indicate that steric effects play a subtle role in the determination of aldol regiochem-istry in unsymmetrical ketones. Although reaction at C-3 is favored for 2-butanone with all of the aldehydes, pivalaldehyde gives more reaction at C-1 than the other aldehydes studied. Selectivity for reaction at C-3 in 2-pentanone is significantly less with all aldehydes, especially pivalaldehyde. 

Aldolase antibodies 38C2 and 33F12 generated by immunization with diketone 1 are capable of accelerating more than 100 different aldol reactions [4, 8, 11, 15, 16]. Some examples of cross-aldol reactions are shown in Table 6.1. For cross-aldol reactions, a variety of ketones are accepted as donors, including aliphatic open-chain ketones (for example acetone to pentanone), aliphatic cyclic ketones (cyclopentanone to cycloheptanone), functionalized open-chain ketones (hydroxyacetone, dihydroxyacetone, fluoroacetone), and functionalized cyclic ketones (2-hydroxycyclohexanone). As with the donors, the antibodies also accept different kinds of aldehyde substrate, for example benzaldehyde derivatives 8-10, a,j5-unsaturated aldehyde 11, and aliphatic aldehydes 12 and 13 with products as indicated in Table 6.1. 

Aliphatic aldehydes and ketones. The mass spectra of formaldehyde, 3-penta-none, 3-methyl-2-butanone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, and 2,3-butanedione have been given as Unknowns 1.9,4.9,4.10,4.16,4.17, and 5.2 those of 2- and 6-dodecanone are Figures 3.10 and 3.11 those of 2-ethylhexanal, 6-methyl-2-heptanone, and 6-methyl-5-heptene-2-one are shown in Figures 9.8 to 9.10. 

Taylor and Flood could show that polystyrene-bound phenylselenic acid in the presence of TBHP can catalyze the oxidation of benzylic alcohols to ketones or aldehydes in a biphasic system (polymer-TBHP/alcohol in CCI4) in good yields (69-100%) (Scheme 117) °. No overoxidation of aldehydes to carboxylic acids was observed and unactivated allylic alcohols or aliphatic alcohols were unreactive under these conditions. In 1999, Berkessel and Sklorz presented a manganese-catalyzed method for the oxidation of primary and secondary alcohols to the corresponding carboxylic acids and ketones (Scheme 118). The authors employed the Mn-tmtacn complex (Mn/168a) in the presence of sodium ascorbate as very efficient cocatalyst and 30% H2O2 as oxidant to oxidize 1-butanol to butyric acid and 2-pentanol to 2-pentanone in yields of 90% and 97%, respectively. This catalytic system shows very good catalytic activity, as can be seen from the fact that for the oxidation of 2-pentanol as little as 0.03% of the catalyst is necessary to obtain the ketone in excellent yield. 

METHYL-4-PENTANONE (108-10-1) Forms explosive mixture with air (flash point 62°F/17°C). Able to form unstable and explosive peroxides on contact with air and/or when in contact with hydrogen peroxide. Reacts violently with strong oxidizers, aldehydes, aliphatic amines, nitric acid, perchloric acid, potassium tert-butoxide, strong acids, reducing agents. Dissolves some plastics, resins, and rubber. 

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