A-Phenyl substituents

The 1-azirines obtained from the vapor phase pyrolysis of 4,5-disubstituted 1-phthalimido-1,2,3-triazoles (157) have been found to undergo further thermal reactions (71CC1S18). Those azirines which contain a methyl group in the 2-position of the ring are cleaved to nitriles and phthalimidocarbenes, whereas those azirines which possess a phenyl substituent in the 2-position rearrange to indoles. 

Phenanthridine (74) was converted by NBS into the 2-bromo derivative (40%) (55JA6379), but the bromine-sulfuric acid-silver sulfate reagent gave low yields of 1-, 4-, and 10-bromophenanthridines in the ratio (1 6.4 9.5), a reactivity order which contrasts with that found in nitration (1 > 10 > 4 > 2) (69AJC1105). Phosphoryl chloride converted phenanthridine 5-oxide into the 6-chloro derivative, but when that position was blocked by a phenyl substituent, the reductive chlorination process gave a 2-chloro compound (84MI2). 

Thermal rearrangement of 2-vinylaziridine 203, with an electron-withdrawing substituent on the nitrogen atom, at reflux in decalin predominantly yielded 2-pyr-roline 204 along with some 3-pyrroline derivatives 205 (Scheme 2.50) [79]. A similar reaction was also observed with l-alkyl-2-phenyl-3-vinylaziridines 206 [80]. From these observations, the nature of the products formed depends on the natures of the substituents on the aziridine ring if the ring carbon carries a phenyl substituent, the thermolysis in most cases preferentially yields 2-pyrrolines. 

A common feature of the compounds that give extensive syn addition is the presence of a phenyl substituent on the double bond. The presence of a phenyl substituent diminishes the strength of bromine bridging by stabilizing the cationic center. A weakly bridged structure in equilibrium with an open benzylic cation can account for the loss in stereospecificity. 

The proximity of carbon-carbon double or triple bonds or a phenyl substituent, as in allylic, propargylic, or benzylic systems, has very little impact upon a fluorine substituent s chemical shift (Scheme 3.53). Note that one would not expect allyl fluoride and methallyl fluoride to have the same chemical shift. 

Some typical proton and carbon chemical shift and coupling constant data for allylic and benzylic systems are given in Scheme 3.54. An alkenyl substituent or a phenyl substituent on either a CH2F or a —CHF- group has virtually no effect upon that carbon s chemical shift, and they also only affect the proton chemical shift by about 0.5 ppm. 

A phenyl substituent or an additional conjugated double bond at the (3-position does not affect the chemical shift any differently than does an alkyl substituent. 

A phenyl substituent at the y-carbon atom is a much weaker electron donor in comparison with the discussed above ethoxy and morpholin-4-yl groups. Nevertheless, l-(y-phenylallyl)benzotriazole 484 is still lithiated exclusively at the carbon a as it is evident from its reaction with aldehydes and ketones leading to dienes 486, resulting from... 

As a result of the inductive and hyperconjugative effects it is to be expected that tertiary carbonium ions will be more stable than secondary carbonium ions, which in turn will be more stable than primary ions. The stabilization of the corresponding transition states for ionization should be in the same order, since the transition state will somewhat resemble the ion. Thus the first order rate constant for the solvolysis of tert-buty bromide in alkaline 80% aqueous ethanol at 55° is about 4000 times that of isopropyl bromide, while for ethyl and methyl bromides the first order contribution to the hydrolysis rate is imperceptible against the contribution from the bimolecular hydrolysis.217 Formic acid is such a good ionizing solvent that even primary alkyl bromides hydrolyze at a rate nearly independent of water concentration. The relative rates at 100° are tertiary butyl, 108 isopropyl, 44.7 ethyl, 1.71 and methyl, 1.00.218>212 One a-phenyl substituent is about as effective in accelerating the ionization as two a-alkyl groups.212 Thus the reactions of benzyl compounds, like those of secondary alkyl compounds, are of borderline mechanism, while benzhydryl compounds react by the unimolecular ionization mechanism. 

ASYMMETRIC HYDROGENATION OF VINYLPHOSPHONIC ACIDS CARRYING A PHENYL SUBSTITUENT AT C2... 

PN and Parent Exo PX) have unsubstituted norbornenyl rings and differ from each other only in the stereochemistry of their ring fusion. These compounds have been elaborated by the incorporation of either a phenyl (tf>) or a carbomethoxy (C) group in the bridgehead (B) or vinyl (V) positions. Thus, the notation VN represents PN with a phenyl substituent at a vinyl position, while CBX represents PX with a carbomethoxy substituent at the bridgehead position. The isomerization and polymerization chemistry of these nine compounds (PN, PX, 4>BN, (jiVN, (jiVX, CBN, CBX, CVN, CVX) are the main concerns of our work. 

Moreover, a variety of other drugs of synthetic origin, containing a phenyl substituent, do not suffer any aromatic hydroxylation, neither in animal systems nor in microbial systems they often correspond to trisubstituted amino group containing derivatives, where -dealkylation is a major detoxification pathway and probably results in products exhibiting a sufficient decrease in hydrophobicity. 

Acyclonucleosides having a phenyl substituent on the C-T position as in 883 was prepared by condensation of the dioxolane 882 with bis(tri-methylsilyl)thymine in presence of SnCU (90GEP3906357). 

Some control of regioselectivity in favour of the tail-to-tail hydrodimer can be achieved with a phenyl substituent in the tail position and any group other than hydrogen in the head position. Reduction of cirmamaldehyde 34 shows poor regio-... 

The chlorinated intermediate 255 is eliminated and cycloadds to Cjq, yielding pyrazo-linofullerenes of the structure 257 (Scheme 4.42). The 4-nitrophenyl-group can be replaced by a 4-methoxyphenyl- or a phenyl substituent. In this reaction various aromatics and substituted aromatics are tolerated as residues R (e.g. furan, ferrocene, pyrazole or benzene and substituted benzene). The nitro group of the nitrophenyl residue can be reduced with Sn-HCl to the aniline derivative, which can be further functionalized by amide coupling with acid chlorides [311]. 

An unusual intramolecular addition of one ortho C-H bond of a phenyl substituent across the C3=C4 bond in 20 (Scheme 3.33) is observed on thermolysis of 20 in CHCI3 [7]. A similar complex is also formed when the corresponding dppm complex is generated in situ from [Cl(dppm)2Ru-C = C-C = C-C(Ph)20SiMe3] and HBF4 in CH2CI2 [30, 31]. This transformation is actually the parent of the later commonly observed allenylidene to indenylidene intramolecular rearrangement. 

Deprotonation of either the (4S.5R)- or (4/ ,5S)-enantiomer of 3-acyl-1,5-dimelhyl-4-phenyl-2-imidazolidinones 4 by lithium cyclohexylisopropylamide (LICA)1 or diisopropylamide2 furnishes chiral, supposedly chelated enolates, very similar to those enolates obtained from 2-oxazolidi-nones (see Section 1.1.1.3.3.4.2.1.). With LICA the. yyn-enolate is formed exclusively, as shown by O-silylation of the enolate with /ert-butylchlorodimethylsilane1. Attack of an electrophile, such as a haloalkane, from the less hindered side furnishes products (usually crystalline) with a moderate to high degree of diastereoselectivity (see Tabled)1 2. The diastereoselectivities observed in comparable alkylation reactions of the 3-acyl-4-cyclohexyl-l,5-dimethylimidazo-lidinone 3b are superior to those obtained with the 4-phenyl derivative 3a2,7. Thus, as also observed in similar alkylations with oxazolidinones10 (see Section 1.1.1.3.3.4.2.1), a phenyl substituent on the chiral auxiliary seems to be relatively inefficient as a steric control element. 

Using diethyl ether as solvent, SAMP/RAMP-hydrazones of acyclic ketones are alkylated in good chemical yield and generally enantiomeric purities of > 90 % are achieved (see Table 3). Most prominent is the preparation of the alarm pheromone of the ant, ( + )-(5T)-4-methyl-3-hep-tanone, which proceeds with practically complete asymmetric induction5,38. Lower enantiomeric excesses (10-30%) are obtained in the alkylation of ketones which contain a phenyl substituent at the alkylated carbon3,8. 

Enlargement of the aromatic residue in (S)-ethyl O-benzoyllactate by annelation with a benzo group (k) or introduction of a phenyl substituent (m) leads to a significant increase of the optical yield. Remarkable is that the optical yield also increases when the photosynthesis starts from (1 + 2+1) instead of (1+4). Irradiation of (1 + 2+ 1) in S-(+)-ethyl O-benzoyllactate gives an optical yield of 1.7%. 

In 1969, Elschenbroich and Cais reported the ESR spectra of several ferrocenyl anion radicals, including benzoyl, p-tolyl, p-carbomethoxy-benzoyl, p-nitrophenyl, p-cyanophenyl, and nitroferrocene, prepared by electrolytic reduction in either acetonitrile or DMF (5S). In general, the ferrocenyl group destabilizes the anion radicals compared to a phenyl substituent. When both groups are present, delocalization of the unpaired electron into the phenyl substituent is more extensive, and the ESR spectra resemble, for the most part, anion radicals of substituted aromatics. There is small spin density in the ferrocenyl moiety, which appears as small hyperfine couplings for the cyclopentadienyl protons ortho to the point of substitution (38). 

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