Ketone units

Key intermediate 2 (Scheme 1), complicated though it may be, is amenable to a retrosynthetic maneuver that significantly simplifies the synthetic problem. The /J-hydroxy ketone unit in 2 constitutes... 

This paper reports a study of the photochemistry of polymers and copolymers containing o-tolyl vinyl ketone units. 

A novel approach to achieve high regioselectivity was recently developed by Yang and coworkers, in which the in-situ-generated dioxirane functionality, contained within the substrate, oxidizes the secondary 5c-h bond rather than the more reactive tertiary yc-H bond, due to a favorable concerted transition state (equation 31). A limitation of this method, however, is that the ketone unit has to be incorporated into the substrate molecule at the appropriate position, normally a rather unpractical and cumbersome task. Moreover, such a process is necessarily stoichiometric in practice and, thereby, it lacks appeal since nowadays catalytic enantioselective oxyfunctionalizations are in vogue ... 

Now it will be necessary to elucidate the location of the butyl isopropenyl ketone unit in the polymer chain. The spin-lattice relaxation time, Tj., of the protons in the polymer and oligomer was measured. The Ti of methylene protons adjacent to the carbonyl group was nearly the same level as the T of methyl protons in the terminal butyl group or terminal methine proton (Table ) but much longer than the T of the protons in interior sequences of polymer (13). These indicate that the butyl carbonyl group in the polymer or oligomer locates at or near to the forefront or the end of the chain. 

The results of the polymerization terminated lOmin after the initiation are shown in Table IV. As compared with the results of the polymerization for 5hr, the yield and molecular weight of the polymer and oligomer were lower, but the number of butyl carbonyl group in one polymer molecule was almost constant regardless of the polymerization time. This may indicate that the butyl lsopropenyl ketone unit in the polymer molecule locates at or near to the forefront of the chain. 

The trimer showed the peaks of 127, 158 and 258, while the dimer showed the peaks of 127 and 158. The results strongly indicate that the ketone unit locates at the chain end of the oligomer, which could not be determined by NMR spectroscopy. Then, it is reasonable to assume that the oligomer molecule containing a terminal methine proton has one butyl isopropenyl ketone unit at the chain end. 

The number average molecular weight of the PMMA sample was 24,000, and the amount of butyl lsopropenyl ketone unit in this polymer could be calculated to be 0.42mol% of MMA unit if a polymer molecule was assumed to contain one ketone unit. The amount of the ketone formed in the depolymerization reaction was 0.3mol% of MMA formed and corresponded to about 70% of the theoretical value. The depolymerization of the oligomer also gave low-boiling products in 53% yield, which contained about 9% of butyl lsopropenyl ketone. 

This is the direct evidence for the existence of the ketone unit in the polymer and oligomer chains. 

While a maximum conversion of only approximately 25% of the polymer s repeating units can be obtained in solution, prolonged exposure times also result in a significant decrease in the molecular weight of polymer VI as some degradation also occurs with the liberation of phenol. The mechanism for this degradation is likely to resemble that proposed by Hiraoka and others (25,26) for the radiolysis of PMMA. The 13C NMR spectrum of the polymeric photoproduct shows clearly that the polymer contains a majority of unreacted starting phenyl methacrylate units with also some o-hydroxy ketone units. 

The biosynthesis of the polyketide moiety is thought to involve the condensation of coenzyme A esters of acetic acid with malonyl coenzyme A to give thiol esters of 3-keto acids. Further Claisen condensations with malonyl coenzyme A add further ketone units, leading to 3,5-diketo, 3,5,7-triketo acids and so on as their thiol esters. Intramolecular condensations subsequently afford heterocyclic or aromatic structures (Scheme 275). 

A borosilicate glass microreactor (152 pm (width), 51pm (depth) and 2.3 cm (length)) that was connected to a T-shaped PEEK (poly(ether-ether-ketone)) unit (MicroTee, Upchurch Scientific) was used for the formation of sodium enolate of... 

Polymerization behavior of 4 -methylenespiro[2-benzofuran-2,2 -(l,3-dioxola-ne)] (102) is rather complicated. Han et al. [95] claimed that the resulting polymer consists of two structural units (103 and 104), but Pan et al. [96] later proposed a structure containing ketone units (105) instead of keto-ester units 103. 

Lee, Kun-Soo, et al., Preparation of Epoxy Resins Containing Ether Ether Ketone Unit and Then-Thermal Properties, Bulletin of Korean Chemical Society, vol. 22, no. 4, 2001. 

With the enantioselective intramolecular benzoin reaction established as a synthetic tool, and in combination with our efforts in the synthesis of bioactive natural products bearing a quaternary a-hydroxy ketone unit (Davis and Weismiller 1990 Heller and Tamm 1981), such as the 4-chromanone derivative (S)-eucomol (Bohler and Tamm 1967 Crouch et al. 1999), a catalytic asymmetric synthesis of various 3-hydroxy-4-chromanones brought about by the chiral triazolium salts 127, 123b and 102 as pre-catalysts was investigated (Enders et al. 2006d). The sterically different pre-catalysts were chosen in order to adjust the catalyst system to the steric and electronic properties of the substrates 128. A screening of the reaction conditions indicated 10 mol% of the... 

A stereoselective Li-NHs reduction of a cyclopentenone has been employed in two different syntheses of the cytotoxic sesquiterpene coriolin (69 Scheme 2). In one synthesis, tricyclic ketone (70) was reduced stereoselectively to alcohol (71) using Li-NHs-methanol. In the second synthesis, tetracyclic enone (72) was converted in a single step to (71). This reduction proceeds by initial cleavage of the cyclopropyl ketone unit of (72) to give ketone (70), which is then reduced to (71). 

However, even activated polymers contain basic (amine) groups resulting both from disproportionation and from side reactions [135,151], e.g., reaction (49). The end groups in anionic polymers are represented by primary amine, activator residue, acyllactam (both N- and a-) and carboxyl groups [134]. In addition, some basic groups other than primary amine are present [126]. A certain fraction of basic groups are ketimine structures resulting from intramolecular cyclization of a terminal amino ketone unit [124]... 

Biichi has modified his original approach to produce ( +)-velbanamine (118) (Scheme 23) and catharanthine. The isoquinuclidine intermediate (119) was degraded to (120). Linking to the indole was followed by a cleavage (121) -+ (122) made possible by the 3-hydroxy-ketone unit, and the intermediate (122) elaborated into velbanamine. 

Conjugate addition of a nucleophile to an alkynyl ketone unit ortho to amino allows interaction of the amine and carbonyl groups and thus the formation of a quinoline. ... 

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