Acta Chimica 65. (1970)
4. szám - ORGANIC CHEMISTRY - Bernáth G.–Kovács K.–Láng K. L.: Stereochemical Studies, VIlI.
350 BERNÁTH et al.: STEREOCHEMICAL STUDIES, VIII Earlier studies (a) 1,2-Acyl migration The N—>-0 acyl migration of 1,2-aminoalcohols is íveli known. It lias been the subject of several reviews [5—10], and a number of kinetic studies have been reported. N—*0 acyl migration was first observed with aminophenols in 1883 [11], but its interpretation and extension to aminoalcohols followed only after a long time [12]. N->0 acyl migration has been studied in detail with arylalkanolamines by Bruckner [13], Fodor et al. [14] and other authors [15—25]. A number of kinetic studies have been published in connection with ephedrine and related derivatives [15, 19—23]. Non-kinetic investigations on N—>0 acyl migrations aimed at elucidating problems of conformation were recently published [26], erythro- and t/ireo-2-acetamido-l,2-bis(3,4-methylenedihydroxyphenyl)-ethanol being used as the model compound. Acyl migration has also been studied in several cyclic 1,2-aminoalcohol diastereoisomers, such as 2-aminocyclopentanol [27], 2-aminocyclohexanol [28—31, 34], 2-amino-3-liydroxytetralin [32], l-amino-2-hydroxytetralin, l-amino-2-hydroxyindane [33], inosamine [34], etc. An intramolecular mechanism of 1,2 N —»- О acyl migration was proposed at the early stages of the studies [35, 36]. Contributions to the elucidation of the mechanism are due mainly to Fodor [5], Koczka and Fodor [8], Fodor and Kiss [28], and to Welsh [15, 25]. Subsequent kinetic studies [19, 30, 31] provided further information about the conditions influencing the reaction. Some aspects of the mechanism of N—>-0 acyl migration are still the object of research. In a paper published in 1967, Welsh [25] showed by tracer studies that water participated in N->-0 acyl migrations which took place by the inversion mechanism. Welsh used N-benzoylephedrine and N-benzoylpseudo-ephedrine as model compounds, which had also been extensively studied previously [15, 19]. When the HCl-catalyzed N-^0 acyl migration was carried out in 180-enriched water, the amino ester that formed with inversion was enriched in 180, while that formed with retention was not. According to Welsh [25], N—>-0 acyl migration in 1,2-aminoalcohols may occur by two competitive mechanisms in agreement with earlier views [8, 15]. The retention (R) and inversion (I) mechanisms are shown in Figs 1 and 2, respectively. (h) 1,3 Acyl migration N—*•0 acyl migrations in 1,3-, and especially 1,4-aminoalcohols have only been studied in a few cases. Though the extension of the acyl migration reaction to 1,3-aminoalcohols had been planned by Fodor [37], and it was used in the determination of the configuration of tropine, psendo-tropine