Acetals, aryl

Diphenyl tellurium diacetate refluxed in acetic acid with styrene in the presence of palladium(II) chloride and sodium acetate, arylated styrene to stilbene and formed biphenyl3. 

Benzyl acetates. Aryl carbonyl compounds (but not others) undergo reductive acetylation at room temperature. 

In 2001, Buchwald reported the a-arylation of esters using not only biphenyl-type ligands but also t-Bu-MAP [217]. The t-butyl acetates could be successfully arylated using DavePhos as ligand and LHMDS as base, and the same system was employed for the formation of a-aryl propionic esters and for the a-arylation of ethyl phenyl acetates. Aryl chlorides could also be used as coupling partners for... 

Hydrogen chloride adds to aryl acetylenes in acetic acid to give mixtures of a-chlorostyrenes and the corresponding vinyl acetate. A vinyl cation, which would be stabilized by the aryl substituent, is believed to be an intermediate. The ion pair formed by protonation can either collapse to give the vinyl halide or capture solvent to give the acetate. Aryl-substituted acetylenes give mainly the syn addition product. 

Thioketene Acetals. Anion (1) reacts with aldehydes and ketones to provide the corresponding thioketene acetals aryl and unsaturated aldehydes and ketones are good substrates for this reaction (eqs 3 and 4). Enolizable alkyl ketones also react to provide thioketene acetals (eq 5). Alternative methods for the preparation of these cyclic thioketene acetals involve the use of phospho-nate derivatives, mixed zinc-titanium organometallic reagents, and iV,iV-dimethyl thioamides. The phosphonate reagents are more nucleophilic than (1) and are superior when competitive deprotonation is a problem. 

Lam P, Clark C, Saubem S, Adams J, Winters M, Chan D, Combs A (1998) New aryl/heteroaryl C-N bond cross-coupling reactions via arylboronic acid/cupric acetate arylation. Tetrahedron Lett 39 2941-2944... 

It follows therefore that ethyl malonate can be used (just as ethyl aceto- acetate) to prepare any mono or di-substituted acetic acid the limitations are identical, namely the substituents must necessarily be alkyl groups (or aryl-alkyl groups such as CjHjCHj), and tri-substituted acetic acids cannot be prepared. Ethyl malonate undergoes no reaction equivalent to the ketonic hydrolysis of ethyl acetoacetate, and the concentration of the alkali used for the hydrolysis is therefore not important. 

The following give abnormal results when treated with chlorosulphonio acid alone, preferably at 50° for 30-60 minutes —fluobenzene (4 4 -difluorodiplienyl-sulphone, m.p. 98°) j iodobenzene (4 4 -di-iododiphenylsulplione, m.p. 202°) o-diclilorobenzene (3 4 3. -4 -tetrachlorodiphenylsulphone, m.p. 176°) and o-dibromobenzene (3 4 3 4 -tetrabromodiphenylsulphone, m.p. 176-177°). The resulting sulphones may be crystallised from glacial acetic acid, benzene or alcohol, and are satisfactory for identification of the original aryl halide. In some cases sulphones accompany the sulphonyl chloride they are readily separated from the final sulphonamide by their insolubility in cold 6N sodium hydroxide solution the sulphonamides dissolve readily and are reprecipitated by 6iV hydrochloric acid. 

Unsymmetrical diaryls may be prepared by treating an aryl diazonium salt solution with sodium hydroxide or sodium acetate in the presence of a liquid aromatic compound. Thus 2-chlorodiphenyl is readily formed from o-chloro phenyl diazonium chloride and sodium hydroxide solution (or sodium acetate solution) in the presence of benzene ... 

The oxidative coupling of toluene using Pd(OAc)2 via />-tolylmercury(II) acetate (428) forms bitolyl[384]. The aryl-aryl coupling proceeds with copper and a catalytic amount of PdCl2 in pyridine[385]. Conjugated dienes are obtained by the coupling of alkenylmercury(II) chlorides[386]. 

An Q-arylalkanoate is prepared by the reaction of aryl halide or triflate with the ketene silyl acetal 74 as an alkene component. However, the reaction is explained by transmetallation of Ph - Pd—Br with 74 to generate the Pd eno-late 75, which gives the a-arylalkanoate by reductive elimination[76]. 

The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

Alkynes with EWGs are poor substrates for the coupling with halides. Therefore, instead of the inactive propynoate, triethyl orthopropynoate (350) is used for the coupling with aryl halides to prepare the arylpropynoate 351. The coupling product 353 of 3,3-dicthoxy-l-propyne (352) with an aryl halide is the precursor of an alkynal[260]. The coupling of ethoxy) tributylstan-nyl)acetylene (354) with aryl halides is a good synthetic method for the aryl-acetate 355[261]. 

Tin enolates of ketones can be generated by the reaction of the enol acetate 733 with tributyltin methoxide[60i] and they react with alkenyl halides via transmetallation to give 734. This reaction offers a useful method for the introduction of an aryl or alkenyl group at the o-carbon of ketones[602]. Tin enolates are also generated by the reaction of siiyl enol ethers with tributyltin fluoride and used for coupling with halides[603]. 

Allylic acetates are widely used. The oxidative addition of allylic acetates to Pd(0) is reversible, and their reaction must be carried out in the presence of bases. An important improvement in 7r-allylpalladium chemistry has been achieved by the introduction of allylic carbonates. Carbonates are highly reactive. More importantly, their reactions can be carried out under neutral con-ditions[13,14]. Also reactions of allylic carbamates[14], allyl aryl ethers[6,15], and vinyl epoxides[16,17] proceed under neutral conditions without addition of bases. 

Various S-nucleophiles are allylated. Allylic acetates or carbonates react with thiols or trimethylsilyl sulfide (353) to give the allylic sulfide 354[222], Allyl sulfides are prepared by Pd-catalyzed allylic rearrangement of the dithio-carbonate 355 with elimination of COS under mild conditions. The benzyl alkyl sulfide 357 can be prepared from the dithiocarbonate 356 at 65 C[223,224], The allyl aryl sufide 359 is prepared by the reaction of an allylic carbonate with the aromatic thiol 358 by use of dppb under neutral condi-tions[225]. The O-allyl phosphoro- or phosphonothionate 360 undergoes the thiono thiolo allylic rearrangement (from 0-allyl to S -allyl rearrangement) to afford 361 and 362 at 130 C[226],... 

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

The reactant corresponding to retrosynthetic path b in Scheme 2.2 can be obtained by Meerwein arylation of vinyl acetate with o-nitrophcnyldiazonium ions[9], Retrosynthetic path c involves oxidation of a 2-(o-nitrophenyl)ethanol. This transformation has also been realized for 2-(o-aminophenyl)ethanols. For the latter reaction the best catalyst is Ru(PPhj)2Cl2. The reaction proceeds with evolution of hydrogen and has been shown to be applicable to a variety of ring-substituted 2-(o-aminophenyl)ethanols[10]. 

Acetylation of 2-phenyl-4-amino-5-benzoylthiazole takes place on the exocyclic nitrogen (49). This exocyclic nitrogen remains the reactive center even with 2-imino-3-aryl-4-amino-5-carboxamido-4-thiazoline (111). Its acetylation with acetic anhydride gives the 4-acetamido derivative (112), which reacts further on heating to yield 2-(acetylimino)-(3H)-3-aryl-5-methylthiazolo[4,5-d]pvrimidin-7-(6H)-one (113) (Scheme 76) (276). 

The nucleophilic reactivity of the oxygen has been observed in acetylation by acetic anhydride of 2-aryl- and 2-heteroaryl-A-2-thiazoline-4-ones (181) (388, 397, 410, 414, 416, 419, 422, 426. 427) and methylation of 5-(4 -chlorophenyl)-A-2-thiazoline-4-one (416) (Scheme 94). 

Amino-4-aryl-5-acetic acid selenazoles were used by Knott (2l i as intermediates in the preparation of T.2, 4.6-naphthoselenazoles (21. 30, 31). 

Similarly, 5-thiazole alkanoic acids and their salts are obtained from thioamides and /3-halo -y-keto acids (695). Thus thioarylamides condensed with 3-aroyl-3-bromopropionic acid (88) in isopropanolic solution in the presence of Na COs give first 4-hydroxy-2-aryl-A-2-thiazoline-5-acetic acid intermediates (89), which were dehydrated in toluene with catalytic amounts of p-toluene sulfonic acid to 2,4-diaryl-5-thiazole acetic acid (90) (Scheme 39) (657), with R = H or Me Ar = Ph, o-, m- or p-tolyl, o-, m-, or P-CIC6H4, 0-, m-, or p-MeOC(iH4, P-CF3C6H4, a-thienyl, a-naphthyl (657). 

With cr-thiocyanatoacetophenones, 4-aryl-2-hydroxythiazoles can be obtained in 80 to 90% yields in an acetic acid solution with the addition of dilute sulfuric acid (87, 392, 416, 428, 484, 519). 

The action of ammonia on N-(aryl-i,3-oxathiol-2-ylidine) tertiary im-inium salts (254) yields linear intermediates (255) that cyclize to 2-amino-4-phenyl thiazoles (256) on crystallization from acetic acid (Scheme 129) (730). 

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