Acid-Mediated Ring-Expansion Reaction of N-Aryl-2-vinylazetidines: Synthesis and Unanticipated Reactivity of Tetrahydrobenzazocines
摘要:
The aza-Clasen rearrangement of N-aryl-2-vinylazetidines has been explored. N-Aryl-2-vinylazetidines were transformed to corresponding tetrahydrobenzazocines in good yields. Unexpectedly, the tetrahydrobenzazocine was unstable and readily isomerized to vinyltetrahydroquinoline in the presence of acid. The mechanism of this ring contraction was studied in detail.
N-Arylazetidines are efficiently obtained in a three-step procedure, providing a wide diversity of derivatives on multigram scale with overall yields of 21–55%. Cheap or easily available acetanilides are used in an adapted aldolization with aldehydes, furnishing β-hydroxyamides with an 81% average yield over 21 examples. Special Mitsunobu conditions have been developed to ensure the cyclization of
The aza-Clasen rearrangement of N-aryl-2-vinylazetidines has been explored. N-Aryl-2-vinylazetidines were transformed to corresponding tetrahydrobenzazocines in good yields. Unexpectedly, the tetrahydrobenzazocine was unstable and readily isomerized to vinyltetrahydroquinoline in the presence of acid. The mechanism of this ring contraction was studied in detail.
Synthesis of Tricyclic Benzazocines by Aza-Prins Reaction
The aza-Prins reaction of 3-vinyltetrahydroquinolines with aldehydes proceeded smoothly in the presence of hydrogen halides, and the tricyclic benzazocine derivatives were isolated in good to high yields. The reaction would proceed through the formation and cyclization of the iminium ion intermediate.