Of -camphorquinone

Other papers of interest in this section report transamination of camphor-3-carbothioamides with secondary cyclic amines, reaction of camphorquinone with dimethyl /S-ketoglutarate, the use of fenchone (212 X=0) in alkene formation from Grignard reagents, bromination of 2-e/itfo-6-endo-dibromobornane to yield 2,3,6-endo-tribromoborn-2-ene, and camphor-enol trimethylsilyl ether formation by quenching the reaction mixture of butyl-lithium and camphor tosyl-hydrazone with trimethylsilyl chloride. ... 

Composite fixing cements were prepared based on a standard methacrylate mixture and incorporating either the step 1 product or a mixture of camphorquinone and p-N, -d i met h I am i n be nzoic acid ethyl ester using an Exakt Apparatebau model roll mill. Testing results are summarized in Table 1. 

An intriguing C-C bond scission of camphorquinone is via rearrangement [205]. The rearrangement, which is induced by a destabilizing a-a disposition in addition... 

Two isomers of camphorquinone monooxime, known as isonitrosocamphor (HCQM) and isonitrosoepicamphor (HCQE), react with Ni(NC>3)2 hydrate in the presence of py affording compounds of composition [Ni(CQM)py3(H20)]PF6,H20 and [Ni(CQE)py3(H20)]PF6-2H20 (pen — 3.04, 3.14BM respectively). A dimeric structure with bridging oxime has been proposed.2506... 

Ligand geometry may alter the coordination properties of dioximes as illustrated by a study of the complexes of camphorquinone dioxime (H2CQD). This ligand exists in four isomeric... 

An asymmetric version of aminoallylation has been developed via a transfer aminoallylation protocol. This methodology involves the initial aminoallylation of camphorquinone 207 with 5-allylpinacol boronate 177 in alcoholic ammonia, furnishing the a-aminoketone 208 stereoselectively, which upon treatment with an aldehyde 209 and achiral allyl boronate 177 leads to the in situ formation of chiral imine 210 followed by allylation to yield the homoallylic amines 212 (Scheme 35) <2006JA11038>. Excellent levels of enantio- and diastereo control were observed for the allylation of a wide array of aldehyde substrates. 

Circular dichroism provides an additional spectroscopic tool for characterization of excited states 35). Considerable interest has also been extended to esr-spectra of anion radicals of a-diketones 36). Circular polarization of the phosphorescence of camphorquinone has been determined, 51). Biacetyl has been the subject of a CIDNP study 152), of fluorescence quenching by a variety of substrates 153), and of steric effects in quenching of triplet states of alkylbenzenes 154). 

Rapid hydrogen transfer occurs between semidione radicals and ground state diketones. This w as illustrated by irradiation of a mixture of camphorquinone (174, A-max 470 nm, Ex = 51 kcal/mole) and tetralindione 68 (Amax 388 nm, ET = 54 kcal/ mole) in 2-propanol at various wavelengths 141). The exclusive product, no matter what the wavelength, was reduced 68 indicating that the equilibrium below lies to the right. Ketyl radicals derived from monoketones, such as benzophenone, transfer... 

Metal-ammonia reduction of bicyclo[2,2,l]heptanones has been examined by Coulombeau and Rassat, who point out that the conformationally more stable forms of substituted alcohols are the exo-isomers in the case of norbornan-2-ol and the 1-methyl homologue, but the endo-isomers in the case of borneol (1,7,7-trimethyl) and fenchol (1,3,3-trimethyl). The same authors have also examined the reduction of camphorquinone [2,3-dioxo-bornane, (249)] with... 

Cerium ammonium nitrate oxidation of camphorquinone gives (201 X = C02Me) as the major product along with the exo-double-bond isomer, methyl 3-methoxy-2,2,3-trimethylcyclopentane-l-carboxylate, and dimethyl camphor ate. 

The most common dental polymers, used for prosthetic purposes and restorative dentistry (filling material), are polymethacrylates.1514 The polymerization process performed directly in the dental cavity has to meet strict demands the reaction must be fast at a temperature below 50 °C and it must avoid the formation of a toxic product. These requirements can be fulfilled by UV curing. For example, a mixture of camphorquinone (586), a chromophore (photoinitiator) with an absorption maximum at 468 nm and an amine 587 as a co-initiator (see also Scheme 6.100), initiates a radical polymerization reaction of the acrylate monomer 588 upon photolysis using a conventional blue lamp or laser (Scheme 6.285). 

The quantum yield provides a measure of the relative rate of chemical reaction vs all deactivation processes. From this point of view, it can be seen from Table 4 that the intramolecular reactions of phenanthrenequinone and the intramolecular reactions of dimethyloctanedione and decanedione are more efficient than the intermolecular reactions of camphorquinone. However, no comparisons of reactivities can be made between different reactions having quantum yields of unity. Further, there is no guarantee that the rate of H-abstraction by excited-state camphorquinone is less than the rate of abstraction by phenanthrenequinone simply because quantum yields are lower with camphorquinone. The possibility that dione may be regenerated by some process subsequent to H-abstraction (e. g. reaction 4 in the general scheme) should also be considered. 

Two different semidione radicals might be formed from an unsymmet-rical dione and these could then undergo further reaction to form two isomeric products. Thus, for example, photolysis 129> of camphorquinone in -xylene solution afforded the isomeric 1,2-adducts 56 and 57 in approximately 2 1 ratio. At first glance it might seem that the prepon-... 

A novel method for generating semidione radicals has recently been reported by Monroe, Weiner, and Hammond 178) who found that the quantum yield for photoreduction of camphorquinone in 2-propanol was markedly enhanced when benzophenone was added and the solution irradiated at wavelength 3660 A where most of the light was absorbed by benzophenone. Instead of benzpinacol formation, the dione underwent photoreduction. Similar enhancement was not observed with jw-methoxy-acetophenone which does not abstract hydrogen from 2-propanol. The conclusion was that the ketyl radical, formed in the efficient H-abstraction reaction of benzophenone, transferred a hydrogen atom to camphorquinone to generate the semidione radical. It was suggested that this phenomenon be called "chemical sensitization . 

Both polar and steric factors play a role in determining the orientation of coupling with the semidione radical. The steric factor is illustrated in the reactions of camphorquinone with aldehydes. Aromatic aldehydes, butyraldehyde and pivalaldehyde reacted 15>13°) exclusively to give 1,4-adducts but acetaldehyde gave a mixture of both 1,2- and 1,4-adducts. 

The ewrfo-configuration of the hydroxyketones 82 and 83 formed from camphorquinone has been unequivocally established 15> and shown to be related to configurations of the aldehyde adducts. This stereochemical result requires attack from the normally more hindered side of the molecule. As discussed earlier (cf. Table 4) m-methoxyacetophenone sensitized the reduction of camphorquinone in 2-propanol, and benzo-... 

Ford, R. A., and F. Parry Electronic and Vibrational States of Carbonyl Compounds — I Electronic States of Camphorquinone. Spectrochim. Acta 12, 78 (1958). 

A solution of 500 g of (-)-camphorquinone in 2.4 L of benzene is heated under reflux with 22 g of 4-methylbenzenesulfonic acid and 375 g of 1,2-ethanediol, using a Dean - Stark head, for 17 h, after which time 98 mL has collected in the aqueous phase. (On occasions, up to 48 h is required for this quantity to collect.) The solution is washed with dil NaOH and HzO, dried over Na2S04, and evaporated. The residue gives the ketal (317 g) as prisms, mp 88 C (EtOH). A second crop is obtained by dilution of the mother liquors with H20 total yield 337.5 g (53%) [a],2,5 +74 (r = 1, EtOH). (lR,4S)-2-exo-Hydroxy-3-bomanone (e.vo-31)31 ... 

Two sterically hindered /V-sulfonylated aminobomeols 42 were prepared from camphorquinone 11 and used after esterification for the formation of enolates which are alkylated or oxidized diastereoselectively (Sections D.1.1.1.3.2., D. 1.5.2.1., D. 1.5.2.3. and D.4.I.). The synthesis of these auxiliaries involves the reaction of camphorquinone 11 with 3,5-dimethylaniline to give the mono-imine by reaction with the sterically less hindered carbonyl group, followed by reduction with boranate and reaction with benzenesulfonyl chloride to give the exo.exo-product. or initial reduction with zinc/potassium hydroxide, then sulfonylation, and finally reduction with boranate to give the endo,endo-isomer21. 

The photochemistry of 1,2-diketones is discussed in a review of halogenovinylene carbonate chemistry.139 The emission characteristics of camphorquinone140 and a cidnp study of camphorquinone photochemistry with aldehydes141 have been reported. 

Bis[( — )-camphoFquinone-a-dioximato]cobalt(ll) hydrate (1). Mol. wt. 467.42, m.p. 240 241". The chiral complex is prepared by the reaction of CoCIa-OHaO with the a-dioxjme of (— )-camphorquinone. 

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