Abstract
In this study, we describe the synthesis of cyclic N-acyl amidines from readily available N-heteroarenes. The synthetic methodology utilized the versatile N-silyl enamine intermediates from the hydrosilylation of N-heteroarenes for the [3 + 2] cycloaddition reaction step. We evaluated various acyl azides and selected an electronically activated acyl azide, thereby achieving a reasonable yield of cyclic N-acyl amidines. We analyzed the relationship between the reactivity of each step and the electronic nature of substrates using in situ nuclear magnetic resonance spectroscopy. In addition, we demonstrated gram-scale synthesis using the proposed methodology.
Highlights
The development of synthetic pathways toward cyclic amidine derivatives is a research area of growing interest
The reactivity of N-silyl enamine from isoquinoline 1a was found to be promising; The reactivity of N-silyl enamine from isoquinoline 1a was found to be promising we began our study with isoquinoline [15]
The result addition of acyl azides with different substituents are listed in Scheme 2
Summary
The development of synthetic pathways toward cyclic amidine derivatives is a research area of growing interest. Most precedent pathways use cyclic amides as starting materials [11–13], our group recently reported a novel synthetic strategy that uses the readily available N-heteroarenes as starting materials and proceeds via a versatile N-silyl enamine intermediate (Scheme 1a) [14,15]. Versatile triazole intermediates are typically formed during the [3 + 2] cycloaddition reactions of enamine derivatives and organic azides These intermediates have been utilized in various synthetic methodologies, such as amidine synthesis with a rearrangement involving nitrogen extrusion [21].
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