Direct Ethylation of Benzylic Amines with in-situ formed Ethylene
Quaternary ammonium salts were used as ethylene source for the direct ethylation of benzylic amines. Simple Hofmann elimination delivers the olefin in situ avoiding the need for gaseous reagents and autoclave technology. The alkylation takes place under rhodium catalysis, requiring inert atmosphere, with exclusive selectivity for the C(sp3)-H bond.
Transition metal catalyzed C-H functionalization has emerged as powerful tool in organic synthesis. Obvious advantages are avoiding pre-functionalized (e.g. halogenated) starting materials and hence the increased atom efficiency.
Direct alkylations are frequently carried out using olefins as alkyl source. Nevertheless, simple ethylation, propylation, or butylation are often prevented since they require the use of gaseous reagents or alternatively the use of toilsome autoclaves or similar high pressure equipment.
Herein we describe a protocol in a conventionally heated sealed-vessel reactor which uses solid and easy to handle quaternary ammonium salts as olefin precursors to overcome the aforementioned drawbacks.
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