Alkylation studies

In support of the alkylation studies, the putative minimum energy conformation of the l, 4-as and 1,4-trans diastereomers of 23 (R4 = Me, Pr1 R1 = Me, Bn, allyl R2 = Me, Bn) were calculated in a high-temperature molecular dynamic study using the Hyper-Chem 3 program and MM calculations. The higher stability of the m-diastereomers was confirmed by the calculations <1997JOC6424, 1998TA4275>. 

The spectra of all metal alkyls studied by Kaesz and Stone (46) show a band at about 2750 cm-1 assignable to an overtone of the symmetric methyl deformation vibration at about 1375 cm-1. If we assign the band at 2812 cm-1 to this overtone, the symmetric methyl deformation frequency would occur at about 1406 cm-1, i.e., near the broad band centered at 1415 cm-1. If we accept this assignment and take account of the fact that... 

Alkylation Studies. Several preliminary experiments were completed to compare the extent of alkylation obtained with our coal pretreatment method to that obtained with Sternberg and Liotta alkylation. Results for Wyodak coal are summarized in Table III. Clearly, our procedure provides a very mild alkylation treatment compared with the other two methods and does not appear to be sensitive to differences in alkyl chain length (methyl vs. propyl). The increase in THF solubiliw was also small this result again suggests only a small extent of alkylation and in addition, shows that only minimal ion exchange (for example Ca by H ) occurred in the coal mineral matter. The effect of each pretreatment method on low severity liquefaction reactivity is discussed in the next section. 

In an enamine alkylation study, piperitone (8 X = H) gave, in addition to the expected dienamines, two rearranged dienamines via ring opening and reclosure hydrolysis yielded the o-menthenones (181Dauben s full paper (Vol. 7, p. 34) on... 

Juaristi, E. Martinez-Richa, A. Garcia-Rivera, A. Cruz-Sanchez, J. S. Use of 4-biphenylyl-mefhanol, 4-biphenylylacetic acid, and 4-biphenylcarboxylic add/triphenylmethane as indicators in the titration of lithium alkyls. Study of the dianion of 4-biphenylylmethanol. /. Org. Chem. 1983, 48, 2603-2606. 

Scheme 1 Major findings of the comparative alkylation study by Pearce and Lappert. Nonisolated labile metal complexes are shown in square parentheses...

F]FBI, 17, has been prepared in three steps (equation 15) and applied for [18F]-labelling of the pharmacologically active spiperone38 18. Model alkylation study using [I8F]FBI has been carried out also. N-alkylation of secondary amines took place under mild (RT) conditions, alkylation of A-methylaniline in a sealed vial required 100 °C and alkylation of amides required the use of TEOH as the base catalyst. 

Until recently, information on alkylation studies reported in the Russian chemical literature was limited to laboratory work. The work of Butlerov and his students on triptene induced one member of their group, El tekov, to study alkylation as a method of preparation of triptene from lower olefins (99,100). Moldavskii and co-workers recently improved this method in an apparent effort at commercial preparation of triptene which is readily hydrogenated to the high antiknock fuel, triptane (242). The alkylation of pentene was accomplished by El tekov with methyl iodide over lead oxide, whereas Moldavskii used methyl chloride and magnesia. Moldavskil s work was probably carried out simultaneously with similar researches in this country. 

Some Considerations In Scaling Up Or Scaling Down Alkylation Studies... 

By the time the alkylation studies were started, the reactivity of the dicarbollide anions toward electrophilic agents had been studied mainly on insertion reactions of boron, or heteroatom, or transition metal into the place of the missing vertex of the icosahedron, restoring its structure. A broad area of metallocarboranes was developed as a result of these studies, which was the subject of many articles and reviews. 

Tetrahydropyranylation of hypoxanthine in DMSO obcurs with acidic catalysis and 2,3-dihydropyran, to produce l,9-bis(tetrahydropyran-2-yl)hypoxanthine (105) and the corresponding 1,7 isomer (106) (66JOC268s). Alkylation studies of 2-oxodihydropurine have been limited and no data are available for the 8-oxo isomer. Methylation of the 2-oxo derivative with methyl iodide in alkaline solution at 80 °C leads to the 7-methyl, then the 3,7-dimethyl derivatives. 

During alkylation studies on 3,6-diethoxyxanthen-9-one (39), stepwise addition of diisobutylaluminum hydride and triisobutylaluminum in hexane yielded 3,6-diethoxyxanthene (40) in 75% yield, although on using these reagents separately the yield of (40) was much less, as shown in Scheme 12. ... 

In early phenol alkylation studies 61), we noticed that alkylation of phenol with ethylene occurred at 204°C, a temperature much higher than that required for ethylation of the much less nucleophilic benzene nucleus (121°C) under similar conditions. Superficially, at least, this appears to violate the classical laws of electrophilic substitution (24). Closer examination of this system 62, 64), however, showed that phenol, at moderately low temperatures, was specifically adsorbed at sites active for alkylation, thus hindering adsorption of ethylene at these same sites, and preventing generation of the electrophile necessary for attack on the phenyl nucleus. That is, alkylation by a Rideal-type mechanism see Scheme 5) cannot occur until temperatures high enough to desorb phenol from the active sites—and allow ethylene to compete for adsorption— are obtained. In such systems, alkylation can be facilitated by imposition of pressure (in the case of ethylene), or use of more polar or higher... 

Dianions derived from sulfur and oxygen containing polycyclic systems have not been reported until very recently. The weak carbon-sulfur bond could discourage attempts to prepare such dianions. Sulfur removal studies by alkali metals were successful due to the properties of the carbon-sulfur bond 182,183). Reductive alkylation studies on model compounds which are relevant to sulfur containing systems demonstrated the stability of hydrocarbon dianions 182). A spectroscopic study performed under mild conditions afforded the characterization of sulfur and oxygen containing dianions 184 186). Benzo[b]thiophene, (73), 1,3-diphenylbenzo[c]thiophene (74) and l,3-diphenylbenzo[c]furan (75) form the respective dianions at low temperature. 

Kramer, G.M. Alkylation Studies in Industrial and Laboratory Alkylation, Albright, L.F., Gold-sby, A.R., Eds. ACS Symposium Series 55 American Chemical Society Washington, DC, 1977 1-26. 

Singh, R.K., Alkylation studies. Part 2. /Jz. v-alkylalion of diethyl cyanomethanephosphonate. Synthesis, 762, 1986. 

Chemical modification studies on the protein in solution can, in general, be rationalised in terms of the structure. For example, alkylation studies with ribonuclease showed that the Na2 position of Hisl2 was preferentially modified. This position... 

As noted earlier in the alkylation study of a-fluoro phosphorus ylides, hydrolysis of the resultant a-fluoro phosphonium salts and a-fluorophosphonates do not necessarily parallel each other. This difference is again exhibited in the hydrolysis of the acylated products of the a-fluoro ylides. For example, the acylation product (10) is readily hydrolyzed at room temperature to give the desired a-fluoro-p-ketoester. The results of the acylation-hydrolysis of (4) with a variety of alkyl, cycloalkyl and aryl acyl halides are summarized in Table HI. 

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