Grouping scheme

These acylating agents are the most commonly used (246). Acid chlorides react with 5-nitro-2-aminothiazoIe (88) despite the deactivating effect of the nitro group (Scheme 61) (247), but more vigorous conditions are required (248). 

HydrOxy-THISs react with diethoxycarbonylazine producing a 1,2,4-triazole via addition, elimination of carbonyl sulfide (29). and subsequent loss of the ester groups (Scheme 20) (30). 

Monoazathiazolocyanines (Tables 2171A.B). The same reactive intermediates and the same conditions as in the case of thiazolomethine dyes are used in the synthesis of this class of dyes, except that the CH group is replaced by a -NH group (Schemes 46 and 47). No j3-azatrimethine thiazolocyamne has been described, in spite of an access method applied with success to other rings (65). 

To sum up, spectroscopic data indicate the amino" form (10) is predominant when R is a hydrogen atom or an alkyl group, while the imino form (11) is predominant when R is an aryl group (Scheme 66). 

Among the less widely exploited interconversion processes are those involving thermal reactions with ethyl azidoformate, which convert furan into A-ethoxycarbonyl-A -pyrrolin-2-one, and thiophenes into A-ethoxycarbonylpyrroles (Scheme 96a) (64TL2185). The boron trifluoride catalyzed reaction of l,3-diphenylbenzo[c]furan with A-sulfinylaniline results in the replacement of the oxygen by an iV-phenyl group (Scheme 96b) 63JOC2464). 

For fV-methylpyrazoIe (99), the molecular ion of which is less intense than pyrazole (a common feature for methyl-substituted pyrazoles (67ZOR1540)), the fragmentation pattern involves the methyl group (Scheme 2). These results were established using H, C and N labelling studies. 

Generation of an anion at the 3-position of certain 2-methoxyisoxazolidines leads to loss of the A-methoxyl group (Scheme 92) (79T213). 

Anions of heterocyclics may attack heterocumulenes to set up systems which can incorporate new atom sequences into the ring by nucleophilic attack on a ring site (such as a carbonyl group). Scheme 32 gives an example (80AG(E)466). 

A versatile oxirane synthesis via (64) is the sulfur ylide approach (B-75MI50504, cf. 76TL457), which in effect inserts a CR2 group into a carbonyl group (Scheme 71). Older, less generally useful versions of this insertion utilize diazomethane or dibromomethane-butyllithium. 

Halide ions may attack 5-substituted thiiranium ions at three sites the sulfur atom (Section 5.06.3.4.5), a ring carbon atom or an 5-alkyl carbon atom. In the highly sterically hindered salt (46) attack occurs only on sulfur (Scheme 62) or the S-methyl group (Scheme 89). The demethylation of (46) by bromide and chloride ion is the only example of attack on the carbon atom of the sulfur substituent in any thiiranium salt (78CC630). Iodide and fluoride ion (the latter in the presence of a crown ether) prefer to attack the sulfur atom of (46). cis-l-Methyl-2,3-di-t-butylthiiranium fluorosulfonate, despite being somewhat hindered, nevertheless is attacked at a ring carbon atom by chloride and bromide ions. The trans isomer could not be prepared its behavior to nucleophiles is therefore unknown (74JA3146). 

Certain nucleophilic sp ies add to carbonyl groups to give tetrahedral intermediates that are unstable and break down to form a new double bond. An important group of such reactions are those with compounds containing primary amino groups. Scheme 8.2 lists some of the more familiar classes of such reactions. In general, these reactions are reversible, and mechanistic information can be obtained by study of either the forward or the reverse process. 

The tautomeric equilibria of 2-aminoimidazoline-5-thiones 238 are shifted to the imino forms 238b when R is an electron-withdrawing group (Scheme 82) [96CHEC-II(3)77],... 

Treatment of macrocycle 278 with an excess of Caro s acid resulted in oxidation of all the sulfur atoms to sulfones and the azo group to an azoxy group (Scheme 181) (99MI4). The oxidation product 279 was formed in 42% yield. Products with smaller oxygen contents were obtained using weaker oxidizing agents. 

The sensitized irradiation of 2-methoxyfuran gave a product (34) deriving from a transposition reaction of the methyl group (Scheme 13) (69TL2767). The 5-methyl derivative 35 was obtained starting from 2-acetoxyfuran (Scheme 13). 

It should be noted that these were the first examples of the Cu-catalyzed crosscoupling of arylhalides with terminal acetylenes. The authors (71IZV1764) carried out the acetylenic condensation with unreactive 4-iodo-l,3,5-trimethylpyrazole, a compound in which the halogen atom is not only found in a position more unfavorable for replacement, but is also further deactivated by the introduction of electron-donor methyl groups (Scheme 40). 

Moreover, when carbamino and nitro groups are simultaneously in the ortho position to the triple bond, isomerization occurs only with participation of the amide group (Scheme 125). 

Although the first ionic liquid expressly categorized as being task-specific featured the incorporation of the function within the cation core, subsequent research has focused on the incorporation of functionality into a branch appended to the cation [11]. In this fashion, a number of task-specific ionic liquids built up from 1-methyl- and 1-butylimidazole have been prepared, produced by means of the reaction between these imidazoles and haloalkanes also incorporating a desired functional group (Scheme 2.3-1). Bazureau has used this approach to prepare imida-... 

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