Carbonyl olehnation

The latter compound undergoes carbonyl olehnation, olefin metathesis and addition to acetylenes . 

Scheme 2.9. Carbonyl Olehnation Using Phosphonate Carbanions...

Scheme2.10. Carbonyl Olehnation UsingTrimethylsilyl-substituted OrganolithiumReagents...

The decarboxylative approach to the ylide formation generated cycloaddition products derived from cycloaddition of the ylide to the carbonyl moiety of the molecule, as opposed to the alkene as seen in previous examples. Kanemasa has reconciled this observation by consideration of the postulated transition state model of the reaction. It was assumed that the steric repulsion of the terminal olehnic substituent and the ylide would favor transition state 309 (Fig. 3.19). Additionally, nonstabilized azomethine ylides have a higher energy HOMO than stabilized ylides, and would therefore prefer the LUMO of the carbonyl than the lower lying alkene LUMO. Formation of fused hve-membered rings would also be kinetically favored over construction of six-membered ring (Scheme 3.103). 

The C-NMR spectrum showed six quaternary carbon signals, four of them in the range of sp -hybridized carbon atoms, which accounted for the two carbonyl functions and the double bond. The upheld shift to 104.3 ppm of one of the olehnic carbons revealed an enol ether. The two low-held sp signals belonged to the carbons of the tertiary alcohols. As an example of the NMR spectra of apicrotoxane the chemical shift values and, in the case of the H-NMR spectrum the coupling constants of picrodendrin A (63) are shown in Scheme 6. 

Many compounds [olehns, alcohols, and carboxyhc acids (or other carbonyl chemistry)] will undergo dimerization reactions. Figure A15-7 shows how carboxylic acids can react with an alcohol to form a dimer [6] (note that it should be loss of water and not carbon dioxide). In RP-UPLC under basic conditions, the elution order would be dihunisal in its ionized form < descarboxydiflunisal < the dimer. Indoles have been shown to dimerize under acidic conditions, and phenols have shown to dimerize under free radical initiated oxidative conditions, usually ortho-phenols [1]. Due to the low bond dissociation energy of the benzylic C-H bond and ease of radical formation, dimerization can occur at the benzylic center. Nalidixic acid undergoes dimerization under thermolysis conditions to produce a dimeric structure [26]. 

Carbouylation of terminai okfins. Terminal olehns can be carbonylated to linear esters in high yield by use of a chloroplatinic acid-stannous chloride couple at 90° and... 

The initial bond formation between the n->ir excited carbonyl compound and an alkene can occur by interaction of the half-filled n-orbital of the [I CO] with the ir-system of the alkene, in a sense transferring a ir-electron to the n-orbital and making a bond between an alkene carbon and the carbonyl oxygen. In this process (common for electron rich olehns) the plane formed by the alkene carbons and their four substituents is perpendicular to the plane of the carbonyl groups and its two substituents (Figure 1). In the... 

On sensitized irradiation with carbonyl compounds such as benzophenone, it is expected that the triplet state of olehns will be produced. However, a radical chain mechanism is sometimes discussed when benzil or biacetyl is used as a sensitizer. Thus, some other experimental evidence such as direct observation of the triplet state by laser photolysis is needed to establish the triplet mechanism even on triplet sensitization. 

Air oxidation of a variety of aliphatic and alkyl aromatic compounda air oxidation of p-nitrotoluene sulfuric acid substitution chlorination of a variety of organic compounds reaction between isobutylene and acetic acid oxidation of ethylene to acetaldehyde (Wacker processes) hydrochlorination of olehns absorption of phosphine in an aqueous soluhon of formaldehyde and hydrochloric acid acehc acid from the carbonylation of methanol oxidation of tri-alkyl phosphine dimerization of olefins. 

The real strength of IR is its ability to identify the strnctnral groups in a molecule, e.g. olehn, carbonyl, and so IR absorption spectroscopy is a powerful identification technique. In particnlar, the fingerprint region below 1500 cm is very dependent on the molecule s environment and it may be possible to identify a molecnle by comparing its transmission bands in this region with spectra from an IR library. Mid IR can also determine the quality or consistency of a sample and the amonnt of components in a mixture. Examples of an FTIR and an FT-Raman instrnment are shown in Fignres 2.16 and 2.17, respectively. 

Early extensive accounts of the Air participation of o, j3-unsaturated carbonyl compounds in [4 -I- 2] cycloadditions detailed their reactions with electron-deficient dienophiles including a,/3-unsaturated nitriles, aldehydes, and ketones simple unactivated olehns including allylic alcohols and electron-rich dienophiles including enol ethers, enamines, vinyl carbamates, and vinyl ureas.Subsequent efforts have recognized the preferential participation of simple a.jS-unsaturated carbonyl compounds (o, j3-unsaturated aldehydes > ketones > esters) in inverse electron demand [4 + 2] cycloadditions and have further explored their [4 + 2]-cycloaddition reactions with enol ethers, acetylenic ethers, ke-tene acetals, enamines, " ynamines, " ketene aminals, and selected simple olefins (Scheme 7-1). Additional examples may be found in Table 7-1. 

The methods for generating acyl ketenes (Scheme 7-V) and their subsequent in situ participation in [4 + 2] cycloadditions with a wide range of hetero- or olehnic and acetylenic dienophiles (Scheme 7-VI), including acyl ketenes, carbonyl compounds,nitriles,isocyanates and isothiocyanates,ketenes,(mines,carbo-diimides, ynamines, ketene acetals, enol ethers,and V-sulfinylamines have been extensively reviewed.Two reports have detailed the 4tt participation of allenic ketones in [4 + 2] cycloaddition reactions [Eq. (51)]. ... 

We reacted the phosphonium salts XXVIa—XXVIc with carbonyl compounds under varied experimental conditions. It was shown that when the oleHnation was carried out in absolute ether with lithium diisopropylamide as deprotonation agent — in accordance with the reaction under discussion — the phosphonium salt XXVIa and benzaldehyde formed the Schiff base of the cinnamaldehyde XXVII in 77% yield. In comparison the yield is reduced when, in place of the p-N,N-dimethylamino-phenyl residue in XXVIa, the p-methoxyphenyl residue (XXVIb) is introduced. Using approximately the same reaction conditions, it falls to 65% of XXVIII and still further to 36% of XXIX when the cyclohexyl residue is present in phosphonium salt (XXVIc). The reaction of the phosphonium salt XXVIa with cinnamaldehyde produced only 20% of the expected Schiff base. 

CL973 87BCJ4079). In other words, the competitive ylide trappings in general favor olehnic dipolarophiles rather than carbonyl dipolarophiles, indicating that olefins would be better dipolarophiles toward azomethine ylides. Padwa has established a more quantitative estimate of the relative reactivity of C-unsubstituted azomethine ylide 43 (R = PhCHj) toward a variety of dipolarophiles (87JOC235). Reactivities relative to that of benz-aldehyde (1.0) are shown in parentheses benzaldehyde is less reactive than thiobenzophenone (1.2), dimethyl fumarate (1.9), and Al-phenylmaleimide... 

Dithioacetals are recently employed as a carbene synton. Titanium carbenes prepared in situ by reduction of CP2T1CI2 with Mg in the presence of P(OEt)3 followed by addition of dithioacetals are effective reagents for olehnation of carbonyl compounds (Eq. 3.38) [152]. 

In slightly acidic conditions, the hydration of olehn gives halo-alcohol, which decomposes to carbonyl compound, as outlined below. ... 

Carbonylation. Dialkylchloroboranes have also been used in the preparation of asymmetric ketones via reduction-hydroboration-carbonylaton protocol. In the presence of 1.0 equiv of trimethyl silane, IpcBCl2 is reduced to IpcBHCl, which selectively hydroborates terminal olefins faster than internal olehns, furnishing the dialkyl chloroborane. Upon further reduction of the R2BCI with LiAlH4, the internal olefin undergoes hydrobora-... 

The addition of the Co—H bond to unsymmetrical olehns is relatively nonspecific. Propylene ordinarily gives mixtures of butyraldehyde and isobutyraldehyde although the former appears to predominate (176). Phosphines, which are sometimes added as carbonylation catalyst promoters, favor the formation of straight-chain products from terminal olefins. 

The reaction of a-bromo-a,p-unsaturated ketones with diethyl phosphonate and triethylamine affords p,y-unsaturated ketones selectively (Scheme 2.5) [15]. This process comprises reduction of the bromide and deconjugation of an olehnic moiety. a-Bromo-a,p-unsaturated carbonyl compounds are readily prepared by treatment of l,l-dibromo-2-siloxycyclopropanes with diethyl phosphonate. This finding makes it possible to prepare p.y-unsaturated ketones from l,l-dibromo-2-siloxycy-clopropanes in one pot. As one of the plausible reaction paths, the a-bromo-p,y-unsaturated ketone, arising from the intervention of the dienol, is subjected to debromination with diethyl phosphonate and triethylamine to give the p,y-unsaturated ketone. 

Several metal carbonyls are known to react with l,3,S-cycloheptatriene to give metal complexes in which carbonyl groups have been displaced by three olehnic bonds and it seems possible that an analogous reaction might... 

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