Carbonyls substitution

Surprisingly carbonyl-substituted carbanions of phosphonates, in which the negative charge is delocalized over two oxygen atoms, are much more nucleophilic than the corresponding phosphoranes. This effea has first been observed by Homer, and has often been utilized in the synthesis of acylated olefins (R.D. Clark, 1975). 

The Cornforth rearrangement involves the thermal interconversion of 4-carbonyl substituted oxazoles, with exchange between the C-C-O side-chain and the C-C-O fragment of the oxazole ring. These reactions generally involve compounds where a heteroatom (-OR, -SR, -Cl) is attached to the 5-position (R2) of the starting oxazole. 

Rotational equilibria of 2-carbonyl substituted thiophene and furan derivatives were calculated and show that the 2-substituent favors the anti-isomer in thiophene <96MI199>. NMR shifts of 35 alkyl 3-hydroxythiophene-2-carboxylates and 3-alkylamino-l-(3-thienyloxy)-2-propanols have been compiled and analyzed <96HC17>. 

Halide substituted isoxazolines 371a-f gave bicyclic dihydropyridones 374 after rearrangement. Methoxycarbonyl substituted isoxazolines 371g-k gave the lactams 375, whereas carbonyl substituted isoxazolines 373a-e gave pyrroles 376 (Scheme 51). 

Isaacs, L., and Diederich, F. (1993) Structures and chemistry of methanofullerenes a versatile route into N-[(methanofullerene)carbonyl]-substituted amino acids. Helv. Chim. Acta 76, 2454-2464. 

I.4.I.4. Synthetic Biologically Active Compounds Silyl- and carbonyl-substituted isoxazoles have been prepared and screened for their cytotoxic activity (497). Some exhibited moderate cytotoxicity toward the HT-1080 and MG-22A cell lines. The highest activity level has been displayed by 3-methyl-5-diphenyl-methylsilylisoxazole. 

Scheme 20.45 Synthesis and cyclization of carbonyl-substituted enyne-allenes.

The chemical shifts of exocyclic methylene protons are very close to the calculated value of 4.65 ppm for four-, five- and six-membered rings not surprisingly the three-membered ring proves to be exceptional. There are also some differences in the effect exerted by carbonyl substitution in rings of different size and in the chemical shifts of radialenes. 

In the nitro- and carbonyl-substituted [2.2]paracyclophanes the most basic position is at the oxygen of the substituent, and substitution occurs in the pseudo-geminal position. 

DCC) proceeds with much higher enantioselectivity (e.e. up to 45%). Likewise, a much higher degree of asymmetric induction was observed in the Pummerer reaction of optically active a-carbonyl-substituted sulfoxides carried out in the presence of DCC (303) to give the a-acetoxy-a-p-toluenesulfenylacetic acid derivatives 278. 

The general chemistry of acylpyridinium salts (181) and their role in the nucleophilic catalysis by pyridine of carbonyl substitution reactions have been reviewed and compared with the role of acylammonium salts (182). ... 

Carbonyl substituted 5/7-1,2,3-dithiazoles (45) lose the carbonyl substituent to give a stable aromatic ion (46) as a main peak in their mass spectra (Equation (1)) <8lBCJ354i>. The ring carbonyl... 

The preparation of (128) (Scheme 34) highlights the use of the trifluoromethyl group to increase the dipolarophilicity of a ketone. This activating effect of electron withdrawing groups is also taken advantage of in the preparation of 3-carbonyl substituted 1,2,4-trioxolanes (131) via the ozonolysis of a vinyl ethers in the presence of a 1,2-dicarbonyl compound (Scheme 36) <9iJOC659l>. 

Because the addition steps are generally fast and consequently exothermic chain steps, their transition states should occur early on the reaction coordinate and therefore resemble the starting alkene. This was recently confirmed by ab initio calculations for the attack at ethylene by methyl radicals and fluorene atoms. The relative stability of the adduct radicals therefore should have little influence on reacti-vity 2 ). The analysis of reactivity and regioselectivity for radical addition reactions, however, is even more complex, because polar effects seem to have an important influence. It has been known for some time that electronegative radicals X-prefer to react with ordinary alkenes while nucleophilic alkyl or acyl radicals rather attack electron deficient olefins e.g., cyano or carbonyl substituted olefins The best known example for this behavior is copolymerization This view was supported by different MO-calculation procedures and in particular by the successful FMO-treatment of the regioselectivity and relative reactivity of additions of radicals to a series of alkenes An excellent review of most of the more recent experimental data and their interpretation was published recently by Tedder and... 

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