1,2-Alkyl/aryl shift

In addition to this latter work, a silver-catalyzed 1,2-alkyl/aryl shift is also possible with allenyl ketones (16), giving, as before, highly substituted furans (17, Scheme 5.9).44 Not surprisingly, Gevorgyan et al. observed that the migratory aptitude... 

Trisubstituted cyclohexen-2-ones produce fragments which are indicative of an alkyl (aryl) shift to the 3-position. The relative intensities of the peaks m/e = 69 and 131 in the case of (72) suggest a preference for phenyl migration22,24. ... 

Oxidation of the pyrrole ring and alkyl/aryl shift (Deionized water)... 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

The 3//-l,2,4-diazaphospholes formed from the reaction of diazomethane and its monosubstituted derivatives (R CH=N2 R = H, alkyl, aryl, acyl, phosphoryl) could not be isolated due to a rapid 1,5-H shift leading to 27/-l,2,4-diazaphospholes 227. When diazo(trimethylsilyl)methane or [bis(diisopropylamino)phosphino]dia-zomethane was used, the l,5-SiMe3 [or PR2, R = N(/-Pr)2] shift completely dominates over the H shift (289,290). In the case of open-chain or cyclic a-diazoketones, cycloadducts 228 cannot be isolated due to rapid acyl shifts giving 229 and ultimately 230 (289). This transformation offers a versatile method to prepare [h]-fused 1,2,4-diazaphospholes from cyclic a-diazoketones and phos-phaalkynes (289). 

Similar upfield shifts for C-3/5 are observed with an axial R = alkyl, aryl, O or S. An axial methyl at the P atom in the 1-oxide, however, is shielded compared with an equatorial one. 31P resonances of phosphorus oxides and sulfides are strongly deshielded. Some examples show the differences (5 values in p.p.m.) Me3P, -62 Me4P+ I-, 25 Me3P=0, 36 Me3P=S, 59 MesP, unknown. Other physical methods, such asP=0 or P=S stretching frequencies and dipole moments, are sometimes very useful in conformational and structural determinations. 

Some general trends have been observed 38 (i) as for sulphones, resonances of aryl and vinyl sulphonates occur at appreciably higher fields than those of alkyl sulphonates (ii) in alkyl, aryl and vinyl sulphonates, the 33S chemical shift strongly depends on the electronic properties of substituents on the molecule. In the case of 2-substituted ethanesulphonates22 and 3- and 4-substituted benzenesulphonates,3357,59 61 63 the occurrence of a reverse substituent effect has been observed electron-withdrawing substituents cause un upfield shift of the 33S resonance, whereas electron-releasing groups produce a downfield shift. 

NMR spectra of the solution of 69j and 69k with p-TolLi show a remarkable upheld shift relative to those for 69j and 69k, AS = 182 and 212 ppm, respectively, indicating an increase in the coordination number of tin. It is noteworthy that the organos-tannates 69h and 69i react with l,3-bis(methoxycarbonyl)pyridinium chloride to give the corresponding alkylated(arylated) dihydropyridines. ... 

Strains of Pseudomonas putida are very versatile in metabolizing aromatic compounds, particularly to the corresponding 1,2-dihydro-l,2-diols. The hydroxylating enzyme of the P. putida mutant is not strongly substrate specific and alkyl, aryl and halogen functionalities are usually readily tolerated380. Thus, 4-bromobenzoic acid (1, R = Br) is converted to a. v-4-bro-mo-5,6-dihydroxy-l, 3-cyclohexadiene-l-carboxylic acid (2, R = Br) in 80% yield with 98% cc (determined by chiral NMR shift experiments on the 4-nitrobenzyl ester) 375. The absolute stereochemistry, (5R,6R), was determined by a single crystal X-ray analysis. 

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