Rhodium(iii)-catalyzed C–H activation/[4+3] annulation of N-phenoxyacetamides and α,β-unsaturated aldehydes: an efficient route to 1,2-oxazepines at room temperature

Abstract

An efficient Rh(III)-catalyzed coupling reaction of N-phenoxyacetamides with α,β-unsaturated aldehydes to give 1,2-oxazepines via C-H activation/[4+3] annulation has been developed. This transformation does not require oxidants and features C-C/C-N bond formation to yield seven-membered oxazepine rings at room temperature. Further derivation of 1,2-oxazepines leads to important chroman derivatives.

Recent Advances in Transition-Metal-Catalyzed (4+3)-Cycloadditions

“…In the following year, Chen, Hong and Zhao showed that N-phenoxyacetamides 2.14a could similarly undergo the reaction with ,-unsaturated aldehydes 2.14b at room temperature to form 1,2-oxazepines 2.14c (Scheme 2.14a). 29 Interestingly, the dehydration product was not observed and the hemiaminal product 2.14c was the major product of the reaction. During their optimizations, they…”

Rh‐Catalyzed Synthesis of Oxygen‐Containing Heterocycles

“…The reaction took place with high regioselectivity when unsymmetrical aryl-alkyl alkynes were used as coupling partners with the product of phenyl tethered to the oxygen group generated predominantly. An efficient synthesis of 1,2-oxazepines from N-phenoxyacetamides and α, β-unsaturated aldehydes under room temperature through Rh(III)-catalyzed intermolecular [4+3] annulation was reported by Zhao and coworkers (Scheme 6.32) [47]. It is worth noting that 1,2-oxazepine is readily transformed to chroman derivative, which are important building blocks in a number of biologically important molecules.…”

Unified synthesis of mono/bis-arylated phenols via RhIII-catalyzed dehydrogenative coupling

“…In contrast to type 1 reactions, we recently described a series of oxidative C–H functionalization reactions. In the presence of a stoichiometric external oxidant, N -phenoxyacetamides could react with aldehydes or α,β-unsaturated aldehydes using palladium 4 and rhodium 5 catalysis. In these reactions, the N–O bond of the DG remained intact after the reaction and was retained in the products.…”

“…We thought that the unification of type 1 and type 2 into a single reaction would allow general access to products with different oxidation states with controlling the cleavage of the N–O bond. For example, based on an isolated rhodacycle intermediate Inter I 6 from our previous studies, 5 the O–NHAc-directed cross dehydrogenative coupling reactions with simple heteroarenes would be an attractive strategy to access diverse heteroarylated phenol scaffolds ( Scheme 1 ). 1b , d , 7 – 9 …”