Ethers and Thioethers

Thioethers can be obtained either by heterocyclization (Chapter II) or from the reaction between 2-halothiazoles (102) and the sodium salt of 

A 2-methylthio substituent decreases the basicity of thiazole pK = 2.52) by 0.6 pK unit (269). The usual bathochromic shift associated with this substituent in other heterocycles is also found for the thiazole ring (41 nm) (56). The ring protons of thiazole are shielded by this substituent the NMR spectrum of 2-methylthiothiazole is (internal TMS, solvent acetone) 3.32 (S-Me) 7.3 (C -H) 6.95 (Cj-H) (56, 270). Typical NMR spectra of 2-thioalkylthiazoles are given in Ref. 266. 

Isotopic labeling with CD3, substituents effects (56), and general trends in the thiazole series (271) allowed a complete assignement of the major infrared bands for a series of 2-methylthiothiazoles. 

The kinetics of the reaction between 2-methylthiothiazoles and methyl iodide show that the nucleophilic center is the ring nitrogen. The 2-methylthio group decreases the nucleophilicity of the this atom (269). 

Nucleophilic reactivity of exocyclic sulfur appears in acidic medium. 2-AryI thiazolyl sulfones are obtained from the corresponding sulfides by oxidation with HjO- in HOAc at 100°C (272). The same oxidation takes place with alkyl sulfides (203. 214, 273-275) and dithiazolylsulfides (129). However, the same reaction with 2-benzylthio derivatives gives benzylal-cohol and the related A-4-thiazoline-2-thione (169). 

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The same research group has demonstrated a similar intramolecular process in the construction of bicychc adducts 326 (92). The CsF desilyation of precursors 327, after subsequent reaction of the internal dipolarophile, dehvered the expected cycloadducts with complete stereocontrol when either thioether and ether tethers or activated and unactivated dipolarophiles were used. In contrast with intermolecular protocols, the reaction was successful with both activated and unactivated alkenes. In addition, unlike the previous example, formation of both six (n = 2)- and five (n= l)-membered rings occurs (Scheme 3.109). 

This more recent design has evolved from earlier supported columns prepared with propylthiol, propylnitrile, or propyldiphenylphosphine units linked to the silica surface,101 which separate ketones, thioethers, and ethers.102 Ethylenediamine-like binding sites were prepared in early developments by linking N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,103 which derivatized as Cu11 or Cr111 complexes are able to separate hydrocarbons, esters, ethers, and thioethers.104... 

Kawahara (51) found that he could identify spilled asphalts by making the pentafluorobenzyl thioethers and ethers from traces of mer-captans and phenols in asphalts, and separating them by gas chromatography, using an electron capture detector to obtain the distinctive chromatograms. 

Good yields of oi-aminothioethers were obtained on electroreduction of, ]J-disubstituted thioamides in acetonitrile containing tetrapropylammonium perchlorate and an alkylating agent. 2-Aminothioethers and 2-aminoethers were obtained from N-phthalimi-doaziridines by reaction with thiols and alcohols respectively, followed by reduction of the resultant B-hydrazino-thioethers and -ethers. 

Arylhydroxylamines are readily converted into nitroso compounds with DAD at 0°C (eq 1). One example of the conversion of an A,A-dimethylhydrazone to a nitrile has been reported. Sulfur-containing amino acids like methionine and S-ethylcysteine can be oxidized to their sulfoxides in virtually quantitative yields, although another reaction pathway occurs with most other thioethers. Thioethers and ethers usually react with DAD to yield a-hydrazo derivatives by hydrogen abstraction. The initial ether/DAD adducts can be formed thermally at 100 °C or photochemically at much lower temperatures. ... 

SCHEME 1 Selected thioether and ether containing Scluff base ligands. 

These include copolymers of propylene sulphide with 3-10% of allyl glycidyl thioether and which may be considered as a thio-analogue of the propylene oxide-allyl glycidyl ether rubber briefly mentioned in Section 19.5 ... 

Figure 9. Graph of Standard Free Entropy against Standard Free Enthalpy for an Ether, Thioether and Amine...

Irregular 6- and 7-fold coordination of Sb occurs in the complexes of SbCl3 with crown thioethers, and 8-fold coordination has been established in its complex with the j -ether... 

Sjwyer and coworkers have developed an efficient alternative UUmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SnAt reaction. Phenol, thiophenol, or aniline reacts v/ith an appropriate aryl halide, In the presence of KF-aliunina and 18-crovm-6 In acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thio ether as shovm In Eqs. 9.6 and 9.7. ... 

SECTION 129 ETHERS, EPOXIDES AND THIOETHERS FROM ETHERS, EPOXIDES AND THIOETHERS... 

When n electron donors are involved, the XB is preferentially along the axis of the donated lone pair on D. For instance, XBs around ethers, thioethers, and amines feature a tetrahedral arrangement with preferential axial directions for the XBs around hexacyclic amines, and equatorial directions for hexacyclic thioethers [16,17,124,139-142] (Fig. 6). 

Hexadentate ligands l,12-bis(2-pyridyl)-5,8-dioxa-2,ll-diazadodecane and l,12-bis(2-pyridyl)-5,8-dithia-2,ll-diazadodecane have pyridine, amine, and ether or thioether donors offering an N402 or N4S2 donor set. The X-ray structures of the zinc complexes are distorted octahedral with the zinc center encapsulated by the ligand.898... 

Trifluorovinyl Halides and Ethers. Trifluorovinyl halides are quite commonly encountered reagents, while trifluorovinyl ethers have increased interest as novel monomers.3 There is a nice recent paper dealing with the NMR spectra of some trifluorovinyl ethers.4 Fluorine data for a couple of examples of halides, ethers, and thioethers are given in Scheme 6.30. 

We distinguished between alcohols and ethers and between thiols and thioethers, and so we will consider the three relevant exchange quantities for amines, one apiece for primary, secondary and tertiary species. For each exchange reaction, all species are in the... 

For comparison within the chalcogens, the oxidation potentials of the Ph-E-Me series 94, 95b, 96b, and 97b, where E = O, S, Se, Te, respectively, were evaluated by pulse radiolysis.Consistent with the analogous diaryl series, the values for this series indicate that the compounds are increasingly easy to oxidize, with telluride 97b most easily oxidized (0.74 V) and ether 94 least easily oxidized (1.62 V), with these values vs. NHE (Table 10). Eor a broader comparison, series of four or five para-substituted arylmethylsulfides, selenides, and tellurides, 95a-e, 96a-e, and 97a-d were prepared and their values determined in the same manner (Table 10). The same trends were observed, with the thioethers least... 

Aliphatic onium ions such as immonium, oxonium, and sulfonium ions have been introduced as even-electron ionic products of the a-cleavage occurring from molecular ions of amines, alcohols, and ethers or thiols and thioethers, respectively (Chap. 6.2.5). All these and analogous onium ions are capable of further fragmentation reactions, the majority of which are alkene losses [141] yielding fragments of high relevance for structure elucidation. 

If one or more of the hydrogen atoms of a non-metal hydride are replaced formally with another group, R—e.g., alkyl residues—then derived compounds of the type R-XHn-i, R-XHn-2-R, etc., are obtained. In this way, alcohols (R-OH) and ethers (R-O-R) are derived from water (H2O) primary amines (R-NH2), secondary amines (R-NH-R) and tertiary amines (R-N-R R") amines are obtained from ammonia (NH3) and thiols (R-SH) and thioethers (R-S-R ) arise from hydrogen sulfide (H2S). Polar groups such as -OH and -NH2 are found as substituents in many organic compounds. As such groups are much more reactive than the hydrocarbon structures to which they are attached, they are referred to as functional groups. 

In a recent example metalloporphyrins are used as the sensing dyes for a wide variety of odorants, including alcohols, amines, arenes, ethers, halocarbons, ketones, phosphines, thioethers and thiols. An array of four different metalloporphyrins are placed on a substrate and exposed to the vapours for 30 s. The various vapour molecules coordinate onto the central metal atoms of the porphyrins, causing them to change colour and producing a unique four-colour array. The resulting colour array is compared with a library of known chemicals or mixtures and identification is achieved. 

The type of atoms in the tether have little effect on the cycloaddition process. Both alkyl (98,125-127) and ether tethers (128-131) have been extensively investigated and provide similar levels of reactivity. In addition, thioethers (132), amines (133), silanes (134), and silyl ketals (135) are all compatible with the dipolar cycloaddition. 

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