Phenyl acid catalyzed

The general pattern of alkylation of 2-acylaininothiazoles parallels that of 2-aminothia2ole itself (see Section III.l). In neutral medium attack occurs on the ring nitrogen, and in alkaline medium a mixture of N-ring and N-amino alkylation takes place (40, 43, 161. 163). In acidic medium unusual behavior has been reported (477) 2-acetamido-4-substituted thiazoles react with acetic anhydride in the presence of sulfuric acid to yield 2-acetylimino-3-acetyl-4-phenyl-4-thiazolines (255) when R = Ph. but when R4 = Me or H no acetylation occurs (Scheme 151). The explanation rests perhaps in an acid-catalyzed heterocyclization with an acetylation on the open-chain compound (253), this compound being stabilized... 

An interesting class of 2-imino-3-amino-4-thiazolines (408) has been described (578, 701, 726). These 3-amino derivatives of 4-thiazoiine may also be prepared from 2,3-diaminothiazolium salts (406) in basic medium (101) or through the acid-catalyzed rearrangement of 2-acylaminoimino-3-phenyl-4-phenyl-4-thiazolines (407) (Scheme 233) (99, 724). 

Migration to the developing electron sextet at nitrogen is not restricted to hydrogen. In (79) there is methyl migration with formation of methylamine and acetone in the acid-catalyzed decomposition of (80), phenyl migration leads to aniline and acetaldehyde. 

The acid-catalyzed hydrolysis of 2-alkoxy-2-phenyl-l,3-dioxolanes has been studied. The initial step is rate-determining under eertain eonditions and is deseribed by the rate law given below, whieh reveals general acid catalysis. 

These groups, along with a number of other trialkylsilylethyl derivatives, were examined for protection of phosphorothioates. Only the phenyl-substituted silyl derivative was useful, because simple trialkylsilyl derivatives were prone to acid-catalyzed thiono-thiolo rearrangement. Other trialkylsilylethyl derivatives also suffer from inherent instability upon storage,but the trimethylsilylethyl group has been used successfully in the synthesis of the very sensitive agrocin 84 and for intemucleotide phosphate protection with the phosphoramidite approach. 

Quantitative measurements of the rate of acid catalyzed rearrangement of 3-methyl-l-(2-thienyl) allyl alcohol (178) to 1-methyl-3-(2-thienyl)allyl alcohol (179) showed that (178) rearranged forty times faster than the phenyl analog but about three times slower than the... 

Oae found that for both base- and acid-catalyzed hydrolysis of phenyl benzenesul-fonate, there was no incorporation of 0 from solvent into the sulfonate ester after partial hydrolysis. This was interpreted as ruling out a stepwise mechanism, but in fact it could be stepwise with slow pseudorotation. In fact this nonexchange can be explained by Westheimer s rules for pseudorotation, assuming the same rules apply to pentacoordinate sulfur. For the acid-catalyzed reaction, the likely intermediate would be 8 for which pseudorotation would be disfavored because it would put a carbon at an apical position. Further protonation to the cationic intermediate is unlikely even in lOM HCl (the medium for Oae s experiments) because of the high acidity of this species a Branch and Calvin calculation (See Appendix), supplemented by allowance for the effect of the phenyl groups (taken as the difference in between sulfuric acid and benzenesulfonic acid ), leads to a pA, of -7 for the first pisTa of this cation about -2 for the second p/sTa. and about 3 for the third Thus, protonation by aqueous HCl to give the neutral intermediate is likely but further protonation to give cation 9 would be very unlikely. 

Chiang, Y. A. Kresge, J. Zhu, Y. Flash photolytic generation of o-quinone a-phenyl-methide and o-quinone a-(p-anisyl)methide in aqueous solution and investigation of their reactions in that medium. Saturation of acid-catalyzed hydration, j. Am. Chem. Soc. 2002, 123, 717-722. 

Figure 1. Hydrolysis pH-rate profiles of phenyl acetate (lower) and a substituted 2-phenyl-l,3-dioxane (HND). Phenyl acetate profile constructed from data of Mabey and Mill (32), HND profile from data of Bender and Silver (33). Phenyl acetate reacts via specific-acid catalyzed, neutral, and base-catalyzed transformation pathways. The pseudo-first-order rate constant is given by Kobs = K(h+) [H+] + Kn + K(qh-) [0H—]. HND hydrolyzes only via an acid-catalyzed pathway the phenolate anion is some 867 times more reactive than its conjugate acid.

TABLE 3. The nitrogen, the carbon-13 and carbon-14 kinetic isotope effects found for the acid-catalyzed ortho,ortho1-rearrangement of iV-naphthyl-iV-phenyl-hydrazine in 60% aqueous dioxane at 0°C... 

Such stability is only relative, however, given the possibility of the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides of general structure 10.10 (Fig. 10.3) [12], Such a reaction occurs in the in vivo metabolism of styrene to phenylacetic acid the first metabolite formed is styrene oxide (10.10, R = Ph, Fig. 10.3, also 10.6), whose isomerization to phenyl-acetaldehyde (10.11, R = Ph, Fig. 10.3) and further dehydrogenation to phenylacetic acid has been demonstrated by deuterium-labeling studies. A com-... 

This preparation is based on a procedure published by the submitters. 9-Phenylphenanthrene has been prepared previously by the reaction of phenyllithium with 9-chlorophelianthrene, by the high-temperature dehydrogenation with palladimn on charcoal of the Diels-Alder dimer of 1-phenyl-1,3-butadiene, and by the acid-catalyzed cyclization of the alcohol formed from the reaction of 2-biphenylylmagnesium iodide and 2-phenoxy-acetophenone. ... 

Complex 24 was used in thermal and Lewis acid-catalyzed decomposition experiments. Intramolecular C—H reductive elimination from 24 to form exo-2-phenyl-aminonorbornane was demonstrated with labeling experiments [7]. 

Acid-catalyzed reactions of aromatics with monoolefins result in nuclear alkylation. But the base-catalyzed reactions of aromatics with olefins do not result in nuclear alkylation as long as benzylic hydrogens are available. This is true even with aromatics, such as cumene, which have deactivated benzylic hydrogens resulting in facile metalation of the ring. Apparently phenyl carbanions do not readily add to olefins. Pines and Mark (20) found that in the presence of sodium and promoters only small yields of alkylate were produced at 300° in reactions of benzene with ethylene and isobutylene and of t-butylbenzene with ethylene. With potassium, larger yields may be obtained at 190° (24)-... 

Bailey et al. (76LA2240 78JA2202) reported the calorimetric heat of acid-catalyzed isomerization of diastereomeric r-2-phenyl,cis-4-Me,cis-6-di-Me-l,3-dioxanes (Scheme 13). The conformational free energy of phenyl at C-2 (-AG° = 3.12 kcal mol ) is the result of a -SH° = 2.01 kcal mol" favoring the equatorial orientation and a large conformational entropy -AiS = -3.9 cal K mol" also favoring the equatorial conformer. 

Anchimeric assistance may also explain slight changes in mechanism resulting from the presence of a neighboring group. One likely case is the acid-catalyzed hydrolysis of phenylglycosides. Raftery s group" found that the secondary kinetic isotope effect (/tr/ d) was 1.13 for acid hydrolysis of phenyl-4-0-(2-acetamido-2-deoxy-j8-D-glu-... 

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