Azolide salts

Phosgenation of azolide salts (alkali metal, ammonium, phosphonium, etc.) with phosgene in an aromatic or ethereal solvent gave GDI in 87% yield [111]. 

A general review (61 references) of the nucleophiUc and electrophilic reactions of tervalent phosphorus acid derivatives has appeared. The kinetics of the reaction of diisopropyl tetrazolylphosphonite (146 R = Mc2CH) with r-BuOH in dry THF have been studied in the presence of various acids, bases, and salts that catalyse the process. Ammonium azolide salts were found to be considerably more efficient catalysts than the corresponding azole acids or tertiary amine bases. For instance, the relative rates obtained with lV,lV-diisopropylethylammonium tetrazolide, N,N-diisopropylethylamine, and tetrazole were 104, 28 and 1, respectively. ... 

The fact that the isomeric structure of azolides is thermodynamically controlled has been used by Olofson and Kendall to prepare 1-alkylazoles regioselectively (70JOC2246). An asymmetric pyrazole yields two alkylated derivatives (Scheme 21 see Section 4.04.2.1.3 (viii)), but the alkylation with a powerful alkylating agent of the acetylated derivative leads to the less abundant isomer via the salt (249), which is too unstable to be isolated. 

The mesoionic azolides are reported to be relatively stable toward hydrolytic decomposition, but more reactive against amines than the corresponding imidazo-lides.[194] -Protection of the amino compounds (for example by the Boc group) takes place smoothly at room temperature in about one to five hours and with high yield. The amino acids are introduced as sodium salts in aqueous acetone. 

Contrary to carboxylic acids which, under normal conditions, only give salts with amines, dithiocarboxylic acids, RCS2H, are quite reactive in nucleophilic displacement reactions. However, the compounds are unpleasant to handle and, due to their limited stability, often give only low yields of thioamides in the reaction with amines.The approach was successfully employed in the synthesis of thiobenzoyl azolides, e. g. in the formation of (7) according to equation (4). °... 

In amidines transamination is possible,especially useful for such purposes are imidoylimid-azolides, e.g. (341 equation 172). In some cases it is usefiil to prepare amidines by ring opening of suitable heterocycles, which can be achieved by treatment with amines or other nucleophilic (basic) compounds. Examples are the synthesis of amidines firom 1,3,5-oxadiazinium salts (342), 3-amino-l,2-benzisothiazoles (343), 2-ethoxycarbonyl-3,l-benzoxazin-4(4//) one (344), 1,2,5-oxa-diazolo[3,4]pyrimidine 1-oxides (pyrimidofuroxans 345) and l,2,4,6-thiatriazenium-5-olate 1,1-dioxides (345) as shown in Scheme 58. 

Ionic liquids can be used either as solvents or catalysts in chemical reactions. One of the most studied transformations has been the insertion (cycloaddition) of CO2 in epoxide rings to afford cyclic carbonates. In this field, the use of ILs and related catalysts such as choline chloride-metal halide mixtures was reviewed by Kerton and co-workers.Galvan et al. evaluated the use of halide-free PILs as catalysts, using salts having weak organic acid anions, under solvent free conditions. The authors proposed a catalyst decomposition mechanism in order to explain the deactivation of the catalytic system. Similarly Brennecke, Schneider and co-workers studied the competing reactions of CO2 with cations and anions in azolide PILs (Fig. 6) The work shows that careful consideration of both physical properties and chemical reactivity of PILs is needed. 

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