SnCl₄-Catalyzed Aza-Acetalization of Aromatic Aldehydes: Synthesis of Aryl Substituted 3,4-Dihydro-2H-1,3-benzoxazines

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

Keywords:

• 1,3-Benzoxazine
• catalyst
• Lewis acid
• SnCl₄
• synthesis

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.