Methane unsaturated carbonyl compounds

The conjugate addition of bis(iodozincio)methane to -unsaturated carbonyl compound gives y-zincio substituted enolate. As shown in equation 31, bis(iodozincio)methane reacts with. v-cis a,/3-unsaturated ketone in the presence of chlorotrimethylsilane to afford the silyl enol ether carrying a C—Zn bond. These zinc-substituted silyl enolates can be used for further coupling reactions (equation 32)54. 

The next three chapters by Fleming, Armesto, and Rao deal with different aspects of alkene photochemistry alkene [2+2]-photocycloaddi-tions to other alkenes, di-7i-methane (DPM) rearrangements of 1,4-dienes and oxa-di-7i-methane (ODPM) rearrangements of 3,y-unsaturated carbonyl compounds. Photocycloaddition of an ether-tethered 1,6-diene by Cu(I)-catalysis leads to the exo-selective formation of the bicyclic tetrahydrofuran derivative 4 [4]. By direct electronic excitation of a... 

The oxa-di-Jt-methane rearrangement of p, y-unsaturated carbonyl compounds is most commonly observed in rigid systems where isomerisation of the alkene is inhibited. It occurs from the lowest tc -> n triplet state and can be sensitised by triplet sensitiser. 

Of more importance are nitroaldol reactions between mono-deprotonated [ C]nitro-methane and carbonyl compounds. Such condensations can provide /3-nitro[/3- C]-alcohols (Figure 5.69, route B), Michael additions of the nitronate anion to a,/3-unsaturated... 

With aj8-unsaturated carbonyl compounds, 1,2- rather than 1,4-addition is generally the rule with thioacetal anions. Seebach now finds that lithiated bis(methylthio)(silyl)- and bis(methylthio)(stannyl)-methanes undergo 1,4-addition in good yield, affording the Michael adduct, e.g. (62). Other anionic sulphur systems reported to undergo 1,4-addition are trithioformate anions ... 

The photochemical intramolecular oxa-Diels-Alder reaction of several vinyl-alkenoyl methane compounds has been reported Schneider, R.A. and Meinwald, J., Photochemical reactions of a,P-unsaturated carbonyl compounds with olefins, /. Am. Chem. Soc., 89,2023-2032,1967 Meinwald, J. and Kobzina, J.W., Competing pathway in the photochemistry of a 2,5-pentadienone, /. Am. Chem. Soc., 91, 5177-5178, 1969. 

The studies carried out on di-Jt-methane for many years involved the direct or triplet-sensitized irradiation of 1,4-unsaturated systems. The results obtained show that, in general terms, acyclic 1,4-dienes undergo the DPM reaction in the singlet excited state while cyclic and polycyclic dienes are reactive as triplets. > > f " >" The ODPM, 1-ADPM, and 2-ADPM counterparts only occur in the triplet excited state of P,y-unsaturated carbonyl compounds, 8 1-aza-1,4-dienes,and 2-aza-l,4-dienes, > > respectively. An attempt to observe di-7i-methane reactions promoted by SET sensitization was unsuccessful. Thus, Zimmerman and Hoffacker carried out a study on the photoreactivity of 1,4-dienes 21 using 9,10-dicyanoanthrathene (DCA) or 1,4-dicyanonaphthalene (DCN) as electron-acceptor sensitizers. The results obtained show that these compounds undergo intramolecular cychzation to yield dihydronaphthalenes 22 (Scheme 5). The corresponding DPM products are not produced in these photoreactions. 

The Claiscn rearrangement of allyl vinyl ethers is usually an irreversible reaction due to the energetic benefit of forming aC-O double bond. However, in strained bicyclic systems the retro-Claisen rearrangement (3-oxa-Cope rearrangement) of y,<5-unsaturated aldehydes has been observed32. Sometimes equilibrium mixtures of vinyl ether and carbonyl compound were found. For example, the ratio of the valence tautomers, bicyclo[3.1.0]hex-2-ene-6-cWo-methanal to 2-oxabicyclo[3.2.l]octa-3,6-diene, is approximately 7 333. Nevertheless this reaction was used in the preparation of a key intermediate in a prostacyclin synthesis34. 

Compounds derived from Aldehydes and Ketones Reaction between PCI3 and Unsaturated Ketones, Mechanism of Reaction of PClj with Benzaldehyde, 1 4 Addition of Phenyldichlorophosphme, Interaction of Phosphorus Halides with Distyryl Ketone and Phenyl Cinnamylidene Methyl Ketone, Action of PCI3 on turated Aldehydes and Ketones, Interaction of Di-phenylohlorophosphine with Benzaldehyde and Benzal etophenone, Addition of Alkoxy- and Aryloxy-chlorophosphines to Carbonyl Compounds— Phosphorus Derivatives of Dimethylaniline— Derivatives of Dibenzyl-methane and Hydroxymethylene Camphor— Heterocydio Rings containing... 

Typical aminocarboxyhc acids, unsaturated fatty acids bound in hpids, sugars and some other food components are precursors of many important sensory-active carbonyl compounds. Amino acids produce aldehydes mainly as secondary products of alco-hohc or lactic acid fermentations and during thermal processes by Strecker degradation. Formaldehyde (methanal) is formed from glycine, acetaldehyde (ethanal) from alanine propanal and butanal arise from threonine (Figure 8.3), 2-methylpropanal from valine. 

As described in the previous section, a-elimination of dialkyltitanocenes is of limited use for the preparation of titanocene-alkylidenes. Since thioacetals are readily available from carbonyl compounds or through alkylation of bis(phenylthio)methane and related organosulfur compounds, a thioacetal-titanocene(II) system enables the use of different types of carbene complexes. Use of appropriate thioacetals is of crucial importance in this system for the preparation of alkylidene complexes 48, the corresponding diphenyl thioacetals are the starting materials of choice. No carbene complexes are formed from dialkylthio-acetals. To generate vinylcarbene complexes 49, trimethylene thioacetals of aji-unsaturated aldehydes or l,3-bis(phenylthio)propene derivatives are employed (Scheme 4.41). The low-valent titanium species 44 is also easily prepared by the reduction of titanocene dichloride with magnesium in the presence of triethyl phosphite at room temperature. The presence of molecular sieves 4A is essential for the reproducibility of this preparation. In relatively large-scale preparations, care should be taken to control the reaction temperature [92, 93g]. 

The photochemistry of carbonyl compounds has been one of the main areas of research in organic photochemistry for many years. Among aU the different types of carbonyl compounds, P,y-unsaturated ketones have been the subject of extensive studies. The results obtained from these efforts, conducted over a 30-year period, show that, in general, direct irradiation of P,y-unsaturated ketones yields products resulting from 1,3-acyl migration, while triplet-sensitized reactions of these compounds affords cyclopropyl ketones by oxa-di-n-methane (ODPM) rearrangement pathways. Alternative reaction routes, such as decarbonylation, ketene formation, epimerization, [2+2]-intramolecular cycloadditions, Norrish Type I and Norrish Type II reactions, cis-trans isomerizations, and reductions of the C-C double bond, have also been described in some instances, depending on some particular structural features present in the P,y-unsaturated ketone. However, the photoreactivity of these compounds is dominated by the two main processes mentioned above. 

Rest and Graham reported in 1984 that the metal carbonyl complexes CpRh(CO)2, CpIr(CO)2, and Cp Ir(CO)2 can be deposited in methane matrices at 12 K and irradiated to give the corresponding methane oxidative addition products [28]. In addition, the dihydride CpIr(CO)H2 could be irradiated in a methane/argon matrix to generate CpIr(CO)(CH3)H by an alternative route [29]. While the dicarbonyl compounds were not efficient producers of the coordinatively unsaturated intermediate, Perutz found that CpRh(CO)(C2H4) lost... 

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