Crystalline derivatives preparation amides

Crystalline derivatives may be prepared with xanthhydrol (9-hydroxy-xanthen), but the reagent is comparatively, expensive. Xanthhydrol reacts with primary amide,s with the formation of crystalline xanthyl-amides or 9-acylamidoxanthens ... 

The characterisation of a primary aromatic amide is based upon its own m.p. and the identification of the acid (see Section IV,175) produced on hydrolysis. A crystalline derivative may be prepared directly with xanthhydrol (for experimental details, see Section 111,110, 1). 

It should also be mentioned that a combination of ester and amide linkages was frequently used to prepare thermotropic LC polyesteramides. Frequently, the inexpensive p-aminophenol is incorporated. For example, the Vectra B series is a poly(naph-thoate-aminophenolterephthalate) derived from 6-hydroxy-2-naphthoic acid (HNA), p-aminophenol, and terephthalic acid [14]. It is obvious that only a limited amount of p-aminophenol can be incorporated in order to maintain thermotropic liquid crystalline behavior. The amide linkage enhances the intermolecular interactions via hydrogen bridges and improves the solid state properties of the material. 

Sulfonamides (R2NSO2R ) are prepared from an amine and sulfonyl chloride in the presence of pyridine or aqueous base. The sulfonamide is one of the most stable nitrogen protective groups. Arylsulfonamides are stable to alkaline hydrolysis, and to catalytic reduction they are cleaved by Na/NH3, Na/butanol, sodium naphthalenide, or sodium anthracenide, and by refluxing in acid (48% HBr/cat. phenol). Sulfonamides of less basic amines such as pyrroles and indoles are much easier to cleave than are those of the more basic alkyl amines. In fact, sulfonamides of the less basic amines (pyrroles, indoles, and imidazoles) can be cleaved by basic hydrolysis, which is almost impossible for the alkyl amines. Because of the inherent differences between the aromatic — NH group and simple aliphatic amines, the protection of these compounds (pyrroles, indoles, and imidazoles) will be described in a separate section. One appealing proj>erty of sulfonamides is that the derivatives are more crystalline than amides or carbamates. 

IV,N,N -Tris(trimethylsilyl)amidines have been used recently as precursors for a number of inorganic heterocycles and metallacycles,1 some of which are being studied in light of their unusual solid state properties2. Boere et al. reported the synthesis of several aryl-substituted persilylated benzamidines and the related compound /V,N,N, N",N",Ar" -hexakis(trimethylsilyl)-l,4-benezenedicarboximidamide (hereafter referred to as HBDA) 3 the present syntheses, which are generally based on the same reaction of an aryl-substituted carbonitrile with lithium bis(trimethylsilyl)amide, offer more facile routes to representative mono- and polyfunctional carboximidamides (i.e., amidines) as well as the prototypal derivative N,N,N -tris(trimethyl-silyl)formimidamide.4 As before, the crystalline diethyl ether adduct of lithium bis(trimethylsilyl)amide5 is favored over the nonsolvated amide in these syntheses the preparation of the diethyl ether adduct is also described here. 

In all cases except (2) the nitrogen is part of an imide system which forms a chelate complex after deprotonation to the enolate. We used a different approach by using the N,O-acetals 35/36. This was first performed in racemic form to test the diastereose-lectivity of the enolate alkylation (Scheme 8). The diastereomers 35 and 36 are readily separable by chromatography. Analogously, amides 35a and 36a are prepared from O-jV-Boc-amino benzaldehyde. Derivative 36a is crystalline and was submitted to an X-ray crystal structure analysis (Fig. 1). 

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