Pyridines, acyl-, conformations

NQR, 2, 125 Pyridines, acetylalkyl-alkyl deacetylation, 2, 301 Pyridines, acetyltrimethyl-synthesis, 2, 470 Pyridines, acyl-conformation, 2, 162 reactions, 2, 337 Pyridines, alkenyl-ozonolysis, 2, 334 reactions, 2, 334 Pyridines, alkenyldihydro-disproportiation, 2, 62 Pyridines, alkyl-... 

An interesting observation was made by Ferrier and coworkers61 during the acylation of 2,4-boronic esters of methyl a- and /3-d-xylopyranosides, in both of which the pyranoid ring must be in the C.,(d) conformation, and the 3-hydroxyl group must be axially attached. On treatment with benzoyl chloride in pyridine, the a-d-xyloside derivative gave 37% of the 3-benzoate and 19% of unreacted starting-material, but the /3-D-xyloside derivative yielded... 

A less obvious instance is the acylation of l,5-anhydro-4,6-0-benzylidene-D-glucitol. The 1,5-anhydride has a chair conformation, and the 2- and 3-hydroxyl groups are equatorially attached trans to each other, and are, apparently, essentially equivalent91 However, the 2-benzoate and 2-p-toluenesulfonate were obtained almost exclusively on using the acyl chlorides in pyridine, although in the former acylation, an appreciable proportion of the dibenzoate was formed. 

Spiroacylal 2 was designed under the rationale that the constraint of the carbonyl groups into a conformation in which overlap of their 7r-orbitals with the bent bonds of the cyclopropane is assured should dramatically increase the vulnerability of the cyclopropane toward nucleophilic attack.8 Experimental support for this notion is abundant.8 Spiroacylal 2 is considerably more reactive than 1,1-dicarbethoxycyclopropane in such reactions. For instance, reaction of 2 with piperidine occurs at room temperature. The corresponding reaction in the case of the diester is conducted at 110°C.5 Reactions with enolates also occur under mild conditions.8 Compound 2 reacts with the weak nucleophile pyridine at room temperature to give a betaine.8 An illustrative mechanism for the reaction of the acylal 2 with aniline to afford 2-oxo-l-phenyl-3-pyrrolidinecarboxylic acid (3) is... 

Direct tri-0-alkylation of calix[4]arenes has been reported to lead to the syn/syn isomer using bases such as BaO, BaO/Ba(OH)2 or CaH2 in DMF " . The tribenzoate of the p-unsubstituted calix[4]arene, one of the first examples of selectively derivatized calix[4]arenes, was obtained as the anti-syn isomer (benzoyl chloride/pyridine) , while the tribenzoate of 2a obtained in toluene with iV-methylimidazole as base (70% yield) was described as the syn-syn isomer, assuming a partial cone conformation with an inverted phenol ring . Both tris(3,5-dinitrobenzoates) of 2a were obtained by acylation with 3,5-dinitrobenzoyl chloride/l-methylimidazole. While 95% of the syn-syn isomer was formed in acetonitrile, 70% of the anti-syn isomer was obtained in chloroform . 

A -Piperideine — see Pyridine, 2,3,4,5-tetrahydro-A2-Piperideine — see Pyridine, 1,2,3,4-tetrahydro-A3-Piperideine — see Pyridine, 1,2,3,6-tetrahydro-Piperideines — see Pyridines, tetrahydro-Piperidine, 1-acryloyl-polymers, I, 284 Piperidine, N-acyl-IJC chemical shifts, 2, 15 Piperidine, 2-alkyl- N-nitro-conformation, 2, 160 Piperidine, 4-amino-synthesis... 

The y-lactbne is an internal ester that also forms with relative ease, provided the sialic acid can assume the open-chain conformation (Figure 8). Reaction of NANA with dicyclohexyl carbodiimide in cold pyridine, for example, produced the lactone in crystallizable form (Derevitskaya et aL, 1966). Small quantities of the 2,6,7,8,9-penta-O-acyl derivatives of NANA-y-lactone were produced by acylation of NANA in cold pyridine with acetic anhydride or benzoylchloride (Khorlin and Privalova, 1967). The Cg-carbonyl of the lactone can exist in both keto (XXVII) and enol (XVII) forms, the latter being susceptible to ozonolysis (Figure 6). 

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