Abstract
Direct allylboration of various acyclic and cyclic aldimine, ketimine and indole substrates was performed using allylboronic acids.
Highlights
Reaction of allylboronates with imines is an attractive approach for selective synthesis of functionalized homoallyl amines, which are useful synthetic intermediates in pharmaceutical chemistry and natural product synthesis.[1]
Most of the described allylboration methods require external catalysts as the imines have to be activated and/or generated in situ, which complicates the studies of the stereochemistry of self-catalyzed allylboration.1c–h Previously, we have published a convenient method for palladium-catalyzed synthesis of allylboronic acids[6] from allyl alcohols and diboronic acids.[7]
We have demonstrated that allylboronic acids may readily react with imines
Summary
Reaction of allylboronates with imines is an attractive approach for selective synthesis of functionalized homoallyl amines, which are useful synthetic intermediates in pharmaceutical chemistry and natural product synthesis.[1]. Modeling studies for the allylboration of aldehydes have shown that the boat geometry is unlikely in these types of process.[3] Besides, the barrier for the thermal E/Z isomerization of aldimines is high; it is unlikely to happen.[4] Both the E and Z imines gave the same antiselectivity, which is similar to aldehydes[5] and ketones.[6] Acyclic aryl and heteroaryl imines (1a–e) with E geometry react readily with cinnamyl and octenyl boronic acids 2a and b in the presence of molecular sieves at room temperature in a couple of hours (Table 1, entries 1–7).
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