Carbonyl compound-tertiary amine systems

Photoredox systems involving carbonyl compounds and amines are used in many applications. Carbonyl compounds employed include benzophenone and derivatives, a-diketones Ye.g. benzil, eamphoroquinone (85), 9,10-phenanthrene quinone], and xanthone and coumarin derivatives. The amines are tertiary and must have a-hydrogens e.g. A, rV-dimcthylanilinc, Michlcr s ketone 

The reaction between the photoexcited carbonyl compound and an amine occurs with substantially greater facility than that willi most other hydrogen donors. The rate constants for triplet quenching by amines show little dependence on the amine a-C H bond strength. However, the ability of the amine to release an electron is important.This is in keeping with a mechanism of radical generation which involves initial electron (or charge) transfer from the amine to the photoexcited carbonyl compound. Loss of a proton from tlie resultant complex (exciplex) results in an a-aniinoalkyl radical which initiates polymerization. The 

The electron transfer step is typically fast and efficient. Griller ef measured absolute rate constants for decay of benzophenone triplet in the presence of aliphatic tertiary amines in benzene as solvent. Values lie in the range 3-4x10  

Visible light systems comprising a photoreducible dye molecule e g 87) or an a-diketone e.g. 85) ° and an amine have also been described. The mechanism of radical production is probably similar to that described for the ketone amine systems described above (/. . electron transfer from the amine to the photoexcited dye molecule and subsequent proton transfer). Ideally, the dye molecule is reduced to a colorless byproduct. 

More efficient systems can be constructed by having the two components of the photoredox system in the one molecule.  

More efficient systems can be constructed by having the two components of 

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The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

The extent to which secondary and tertiary amines are formed by reductive alkylation is controlled to some degree by the steric bulk of the amine and the carbonyl compound. The more hindered the system, the higher the temperature and hydrogen pressure needed to affect the reaction. While the reductive alkylation of secondary aliphatic amines with formaldehyde takes place under mild conditions (Eqn.l9.52X N,N-dimethylaniline was prepared by reductive alkylation over palladium at 120°C and 15 atmospheres pressure (Eqn. 19.53). 153 54 Reductive alkylation of aniline with acetone over palladium gave a 67% yield of the monoalkylaniline at 100°C and 40 atmospheres pressure but secondary amine formation using the more sterically accessible ketones, 2-tetralone or 2-indanone, took place at room temperature and 4 atmospheres pressure (Eqn. 19.54). 55 Palladium was the preferred catalyst in these reactions since with platinum or rhodium ring hydrogenation was also observed. 54,155... 

Alkyltitanium(IV) complexes having N -dialkylamino ligand systems, RTi(NR 2)3, fail to give nucleophilic additions to carbonyl compounds (Section 1.5.3.1.1). Their reaction with aldehydes leads instead to tertiary amines by addition of both the alkyl moiety of the reagent and one of the N, -dialkylamino ligands (equation 59). The synthetic interest of the reaction is restricted to noneno-lizable aldehydes, since enolizable carbonyl compounds lead to enamines. ... 

An alternative method for the formation of an a,(3-unsaturated carbonyl compound is the elimination of an initially formed Mannich product. The procedure is particularly effective for the formation of (3,(3-bis(unsubstituted) a, -unsaturated carbonyl compounds. The Mannich product 11 can be formed in the presence of a secondary amine and a non-enolizable aldehyde such as formaldehyde (2.12). The Mannich reaction is a useful carbon-carbon bond-forming reaction and the products have found application in the synthesis of, in particular, alkaloid ring systems. The Mannich product may eliminate under the reaction conditions, or can be alkylated to form the quaternary ammonium salt in order to induce elimination. A convenient variation of this method is the use of Eschenmoser s salt, H2C=NMe2 X. For example, Nicolaou s synthesis of hemibrevetoxin B used this salt in order to introduce the required methylene unit a- to the aldehyde 12 (2.13). The same transformation with the corresponding methyl ester, which is less acidic, requires prior enolization with a strong base (e.g. NaN(SiMe3)2) and subsequent quatemization of the tertiary amine with iodomethane and elimination using DBU. 

The RUO4 catalytic system oxidizes secondary alcohols to ketones and primary alcohols to carboxylic acids. Alkenes can be oxidized completely, to produce the corresponding carbonyl compounds, or partially, to produce epoxides this transformation will be discussed below. In addition, methylene carbons adjacent to certain functional groups can be oxidized to the corresponding carbonyl ethers are converted to esters, tertiary amines and amides to amides and imides. 

Due to the low oxidation state of the metal in carbonyliron complexes and ferrates, these species can be applied for the reduction of various carbonyl compounds. Initially, these reagents have been applied in stoichiometric amounts. First examples describe the hydrogenation of a,p-unsaturated carbonyl compounds by carbonyl(hydrido)ferrate complexes to give saturated carbonyl compounds or saturated alcohols. Low valent iron species for the reduction of carbonyl compounds and imines can also be generated in situ from iron(II) chloride and lithium powder in the presence of 4,4 -di-rert-butylbiphenyl. Catalytic versions have been developed subsequently. Thus, pentacarbonyliron functions as a precatalyst for the hydrogenation of aldehydes and ketones in the presence of a tertiary amine as solvent (Scheme 4-322). The catalytically active system probably consists of (tetracarbonyl)(hydrido)ferrate and the protonated amine. ... 

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