Arylthiol

Arylthiols (but not alkylthiols) add to terminal alkynes regioselectively to afford a Markovnikov-type adduct 212 in good yield using Pd(OAc)2 as a catalyst[120]. This result is clearly different from the an/i-Markovnikov addition induced by a radical initiator. The hydroselenation of terminal alkynes with benzeneselenol catalyzed by Pd(OAc)2 affords the terminal alkene 213, which undergoes partial isomerization to the internal alkene 214[121]. 

Perfluorobiphenyl is arylthiolated with a potassium mercaptide at elevated temperature [33] (equaPon 22). 

Truce also examined a few examples of the cleavage of sulphones with sodium in liquid ammonia97 and found essentially similar results except that diaryl sulphones were reduced to sulphinate salts instead of to arylthiolates as with the lithium reductions. Dialkyl sulphones were unreactive towards sodium in liquid ammonia. 

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

The phototransformation of l,2-bis(phenylsnlfonyl)-3,4,5,6-tetramethylbenzene into 2,3,4,5-tetramethyldibenzothiophene-S,5 -dioxide on the action of arylthiolates should also be mentioned. The yield of dibenzothiophene-5, S-dioxide is more than 90%. The addition of m-dinitrobenzene prevents the cyclization. The reaction proceeds as shown in Scheme 7.41 (Novi et al. 1982). 

Methoxypyrazine-2-one Af-oxides 341 were prepared from oxime derivatives 340 by one-pot cyclization in the presence of DCC/DME with subsequent interaction with Me2S04/K2C03 and NaOH (equation 148) . Similar intramolecular cyclizatiou of ester and oxime O-ethers groups iu the presence of lithium arylthiolate also leads to pyrazin-2-one ring formation . ... 

Alkylthioperimidines are simply prepared by alkylation of the 2(l//)-perimidinethione. Arylthio derivatives can be prepared by nucleophilic substitution of a 2-halogenoperimidine by an arylthiolate, a method which is also applicable to the alkylthio derivatives. 

Although there have been few new developments in the period since 1993, halogenopyrazines 42 have been convenient precursors for a variety of pyrazine derivatives. For example, the halogenopyrazines 42 are cyanated by palladium-catalyzed cross-coupling with alkali cyanide or by treatment with copper cyanide in refluxing picoline, to yield cyanopyrazines 48. Alkoxypyrazines 49 are produced by treatment with alkoxide-alcohol, and aminopyrazines 50 are prepared by amination with ammonia or appropriate amines. The nucleophilic substitution of chloropyrazine with sodium alkoxide, phenoxide, alkyl- or arylthiolate is efficiently effected under focused microwave irradiation <2002T887>. 

TABLE 7.6 SYNTHESIS OF 4-(ARYLTHIO)-5(2H)-OXAZOLONES FROM ETHYLCYANOFOR-MATE, KETONES AND ARYLTHIOLS, 141... 

The recent popularity of palladium-catalyzed cross coupling reactions has been extended into the field of pyrimidines as well. For example, the palladium-catalyzed couplings of arylthiols and 2-bromopyrimidine (47) to produce 48 were reported by Thorarensen and coworkers <99SL1579>. 

Chiral aminoalcohols (45), derived from (2S, 4S)-4-hydroxyproline and (S)-proline, respectively, were found to be superior catalysts for the enantioselective 1,4-addition of arylthiols to 2-cyclohexen-l-one to yield 3-arylthiocyclohexanones (46) 82). 

This procedure3 is an example of a simple and general method for preparation of primary and secondary dialkyl and alkyl aryl thioethcrs via alkylation of sodium sulfide or sodium alkyl- or arylthiolates with alkyl chlorides or bromides. The method is an... 

Mononuclear tetrahedral complexes of Co", Zn" and Cd" are also formed with high molar ratios of arylthiolate whereas at lower thiolate concentrations polynuclear species can be obtained. The equilibria existing in acetonitrile solution containing Co", PhS and halide have been postulated as shown in Scheme l,114... 

Unsymmetrical diaryl sulfides (60 R = 2-NO2, 4-NO2, 2,4-(N02)2 R = H, 4-NMe2) were obtained in 80-97% yields from the reaction under PTC conditions of nitro-activated aryl halides with arenethiolates generated in situ from the reduction of the corresponding diaryl disulfides with aminoiminomethanesul-finic acid (61).192 Arylthiolates carrying electron-withdrawing substituents were not sufficiently reactive. The reaction could also be applied to the synthesis of diaryl selenides, but not of ditellurides. 

Chloropyrimidines fused to benzoxazepines are versatile starting materials for development of inhibitors of specific kinases. Thus, the 1-chloro function of pyrimidooxazepine 102 could be substituted with heterocyclic amines <2005BML5474, 2005TL7523, 2006BML5102>, anilines, arylthiols, and phenols <2005JOC9629> to afford the substituted derivatives 103. In the same way, the 3-chloro function of pyrimidine 104 could be substituted (Scheme 12) <2005TL7523>. 

Mixtures of isomers were obtained from the reaction of cis- and trans-a-bromocinnamic acid with arylthiolate ions (Angeletti and Montanari, 1958). The corresponding m- and p-nitro acids reacted faster but gave complete retention. The slower reaction of the unsubstituted acids was probably followed by isomerization of the product, since j9-thioacrylic acids isomerize in similar media (Montanari, 1960). 

In such a small cluster, the surface coverage is 70%, much higher than the percentage measured on flat surfaces covered by arylthiolates (33%).206 The formation of the Au102(SR)44 nanoparticle may be explained with the electronic rules of cluster stability. Considering that each gold atom contributes one valence electron, and that each of the 44 SR thiyl radicals formally takes one electron, a 58 electron closed shell is obtained. A deep analysis and discussion on this landmark achievement have been recently published.207,208... 

One example is illustrated in Scheme 10.12. In the synthetic approach adopted here, the arylthiol functionality was introduced as the fert-butyl sulfide at the beginning of the synthetic sequence. A two-fold HWE reaction between aldehyde 6 and diphosphonate 37 gave OPV3 38. The t-BuS group of 38 was then converted into the AcS moiety by means of AcCl-BBr3. 

An alternative method of preparing the SF5 group was developed in the 1990s using elemental fluorine and an arylthiol. In this process, elemental fluorine is used both as an oxidant and a fluorinating agent. Despite the fact that in the final fluorination, the conversion of SF3 to SF5 is difficult and results in a number of byproducts from ring fluorination side reactions, it provides a more realistic route to the preparation of many pentafluorosulfur phenyl derivatives (Fig. 40) [181],... 

Treatment of ( )-3-alkylamino-3-alkylthiol-1 -(thioaryl)propenes 32 with Ni(0Ac)2.4H20 in EtOH at room temperature afforded the Ni(II)-propenethiolates 33 in excellent yields. Subsequent reaction of 33 with alkyl- or arylthiols at reflux in 1,2-dichloroethane gave novel S,Af-acetals 34. Compound 34 was then converted into 5-aryl-3-(arylthio)isothiazoles 35 by cyclisation and A -dealkylation <02JOC5375>. 

Oxoalkyl- and 3-oxoalkyl-triphenylbismuthonium salts transfer the alkyl groups to various hetero nucleophiles such as piperidine, triphenylphosphane, arylsulfinates, alcohols, arylthiolates, dimethyl sulfide, and metal halides under mild conditions (Equation (132)).214 215 Methyl- and allyl-triphenylbismuthonium salts also alkylate some heteronucleophiles.216 The leaving ability of the triphenylbismuthonio group has been found to be higher than that of the triflate anion. 

Thiols (RSH) behave in a similar way to alcohols but are not so deshielded, as you would expect from the smaller electronegativity of sulfur (phenols are all about 5.0 p.p.m., PhSH is at 3.4l p.p.in.). Alkane thiols appear at about 2 p.p.m. and arylthiols at about 4 p.p.m. Amines and amides show a big variation, as you would expect for the variety of functional groups involved, and are summarized below. Amides are slightly acidic, as you saw in Chapter 8, and amide protons resonate at quite low fields. Pyrroles are special—the aromaticity of the ring makes the NH proton unusually acidic and they appear at about 10 p.p.m. 

---