Abstract
Stannic tetrachloride was an efficient Lewis acid catalyst for the aza-acetalization of aromatic aldehydes with o-arylaminomethyl phenols, and a series of novel aryl substituted 3,4-dihydro-2H-1,3-benzoxazines were prepared in good yields under mild conditions. SnCl4 was a more efficient catalyst for the reaction than p-toluenesulfonic acid, sulfuric acid, and aluminium chloride.
GRAPHICAL ABSTRACT
ACKNOWLEDGMENTS
The authors thank the Natural Science Foundation of Hunan Province (No. 06JJ50016) and the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the State Education Ministry for the financial support of this work.
Notes
a Compound 1a: R = 4-CH3, R1 = 3-NO2C6H4.
b Unless noted, the molar ratio of n(4a)/n(5a) = 1:1.3. The amount of SnCl4 (20 mol%) is based on aminomethyl phenol except for the cases marked in the table. C6H12, cyclohexane; CHCl3/C6H12 = 1:7 (v/v).
c Isolated yield.
d An unknown white solid also formed.
a The molar ratio of n (aldehyde 5)/n (aminomethyl phenol 4) = 1:1.3 for all reactions. The amount of SnCl4 (20 mol%) is based on aminomethyl phenol. CHCl3/C6H12 = 1:7 (v/v).
b Isolated yield.
c Formaldehyde used.