N d O MIGRATION OF ACYLGROUPS
JANUARY1967
119
Participation of Water in the N-0 Migration of Acyl Groups with Inversion of Configuration LLEWELLYN H. WELSH Division of Pharmaceutical Chemistry, U.S . Food and Drug Administration, Washington, D . C . 20204 Received July 20, 1966 Acid-catalyzed N-tO acyl migrations in N-benzoylephedrine and the diastereomeric N-benzoyl-+ephedrine were carried out in an aqueous system enriched in the 0 1 8 isotope. Amino ester product with inverted configuration at the carbon bearing the acyloxy group had an enriched content of 0 1 8 , while that in which configuration was retained had a normal content of the isotope. The results support the concept that N-.O acyl migration in derivatives of 2-aminoalksnols may take place by two competitive mechanisms, one leading to inversion, the other to retention, of configuration at the hydroxyl-bearing carbon atom, with water participating in the inversion process only.
A previous communication from this laboratory1 reported the results of acid-catalyzed N+O acyl migrations in N-benzoyl-( -)-ephedrine (I) and the diastereomeric N-benzoyl-( +)-#-ephedrine (11) (eq 1). The
[
H H C~HH,C-C-CH~ I I
CsH,-&-&--CH3
HA A(CHs)COCsHs I
I
/
CsH6COO NHCHa.HC1 111, erythro configuration
HO H
CsHsCOO H
I
CsH&-d-&-CH3
d
H H
___)
HCl
d(CH,)COCsH6 I1
(1)
I
CsHs-C-C-CHs
I
/
H NHCHa.HC1 IV, threo configuration
data seemed best explained on the basis that rearrangement in aqueous media may occur by two mechanisms, one leading to retention, the other to inversion,
>7'-
y'
Y-F 0 N'CHa \
I\
C,H/
'O*
CHH
D"
X
=
Rr
(1) L. H. Welsh, 3. A m . Chem. Soc., 71, 3500 (1949). (2) Should the attack of carbonyl oxygen at carbon one precede that of water, an analog of G (eq 2) would be the immediate precursor of F. (3) Inter alia, K. Koczka and G . Fodor, Acta Acad. Sci. Hung., 18, 89 (1957). (4) I t could he argued, perhaps with difficulty but also irrefutably, that acyl migration with inversion might occur by an alternative mechanism without obvious analogy, and that the oxygen atoms of the acyloxy group have the identities of those of the hydroxyamide. (5) 5. Winstein and R. E. Buckles. J . A m . Chem. Soc., 64, 2787 (1942); S. Winstein and R. M. Roberts, ibid., 76, 2297 (1953). (6) S. Winstein, H. V. Hess, and R. E. Buckles, ibid., 64, 2796 (1942); 8.Winstein, C. Hanson, and E. Grunwalt, ibid., 70, 812 (1948); S. Winstein, E. Grunwalt, R . E. Buckles, and C. Hanson, ibid., 70, 816 (1948). (7) S. Winstein, E. Grunwalt, and L. L. Ingraham, ibid., 70, 821 (1948). (8) 0.E. McCasland, R. K. Clark, Jr., and H. E. Carter, ibid., 71, 637 (1949); 9. Winstein and R. Boschan,
