6470
J . Am. Chem. SOC.1989, 111, 6470-647 1
Kinetic Scheme I implies a quantitative relationship among k,, the absorbance changes associated with B, and the concentration of A* formed by the actinic flash;26analysis based on this relationship demonstrates that within experimental error, triplet-state quenching is associated only with the electron-transfer process, eq 2, and that other mechanisms leading to deactivation of the excited state in A* (e.g., energy transfer) are relatively insignificant (-
L
I
3
u
I
1
“3
2-
2
I
tH2 t 0-P-N‘
1
N
H O I II Z-NH-C-COBzi
H O I II Z-NH-C-COBzi I
2’
N
H O
I I1 2-NH -:-COB2
H ~ b ’ ’ 0 H3C H 1 I1 I la
H2/Pd/C P
0-P-0-C-C-COOH
I
OH
’A
I
H2C 0
AH2
5
H3C H 0 I l l I I I I 0-P-0-C-C-COBZl I I I BzlO H NH-Z
5
Alkoxy1 Radicals in 1,5-Hydrogen Shifts for Site-Specific, Stereocontrolled Alkylation of Carbohydrates’ J. Cristobal Lopez,’ Ricardo A l ~ n s oand , ~ Bert Fraser-Reid*
N
0 2 = - CI1 - O - C H 2 - 0
Bzl = - C H z - o
Table 1. ’H NMR Data of Compound 6 (Na+ Salt, 0.16 mM in
D20, pD 7.1)15 d values unit (ppm) Hff
3.95 4.14
HP(b)
4.22
Hff HP CH,
3.70 4.74 1.42
coupling constants (Hz) Seryl JH..P = 1.2, J H a . H @ ( a ) = 6.3, JHa,H,+(b) = 3.6 J H @ ( ~ ) , P= 5.0, J H @ ( a ) . H @ ( b ) = 11.3 J~@(b),= p 5.1 Threonyl J H . , ~= 1.9, J H ~ ,
[email protected] J ~ e , p 7.4, J H @ , C= H ~6.6
the rate of the elimination reaction. In conclusion, the N M R data and virtually inertness of com0002-7863/89/1511-6471$01.50/0
Department of Chemistry Paul M . Gross Chemical Laboratory Duke University, Durham, North Carolina 27706 Received March 13, 1989 Two areas of continued interest in our laboratory in developing the organic chemistry of carbohydrates are concerned with enhancing stereoselectivity at (normally) “off-template” sites4 and with the application of radical processes for mild transforma( 1 ) This work was supported by a grant from the National Science Foundation (Grant CHE 8703916). (2) Holder of Research Fellowship from the Consejo Superior de Investigaciones Cientificas of Spain. (3) Research Associate from the Universidad de Santiago de Compostela (Spain); acknowledges a fellowship from the Ministerio de Educacion y Ciencia (Spain). (4) (a) Fraser-Reid, B.; Magdzinski, L.; M o h o , B. J . A m . Chem. SOC. 1984, 106,731. (b) Magdzinski, L.; Cweiber, B.; Fraser-Reid, B. Tetrahedron Lett. 1983, 24, 5823. (c) M o h o , B. F.; Magdzinski, L.; Fraser-Reid, B. Tetrahedron Lett. 1983, 24, 5819.
0 1989 American Chemical Society
