An atom-economical strategy for the
C–H alkenylation and
C–H allylation of arenes by employing cyclopropenes as versatile
alkenylating and allylating reagents is reported, catalyzed by cobalt.
The Co-catalyzed C–H alkenylation process involves sequential
C–H and C–C bond cleavage. Under the optimized conditions,
broad-ranging alkenylated (hetero)arenes were synthesized with complete
(E)-stereoselectivity (up to 91%). The consecutive
C–H allylation proved viable under basic conditions via double-bond
migration of the initially generated alkenyl (hetero)arenes, thus
leading to allylated (hetero)arenes with high stereoselectivity of
olefin (E/Z ratio = 91:9 to 100:0).
A Cp*Co(III)-catalyzed γ-selective C–H allylation/hydroamination
cascade toward the synthesis of 3,4-dihydroisoquinolines (DHIQs) has
been successfully developed, starting from NH ketimines and allyl
carbonates. Notably, highly efficient and γ-selective C–H
allylations were accomplished using γ-substituted allyl reagents,
thus overcoming the issues of poor α/γ selectivity and
low reactivity of previous transition metal-catalyzed C–H allylations.
The stereochemistry of allyl carbonates was a crucial factor, and
synthesis of the DHIQs was achieved using (Z)-allyl
carbonates.
Efficient synthesis of optically active Nfused 1,3-oxazolidines containing quaternary and tertiary stereocenters was achieved via Pd-catalyzed asymmetric (3 + 2) cycloadditions of sulfamatederived cyclic imines and vinylethylene carbonates. Using a chiral phosphoramidite ligand, the cycloadditions proceeded effectively providing sulfamidate-fused 1,3-oxazolidines in high yields (up to 96%) with stereoselectivities (up to 25:1 dr; > 99% ee). Additionally, the scale-up reaction and further transformations of the product were also achieved demonstrating the synthetic utility toward the construction of useful heterocycles such as chiral oxazoline bearing a quaternary stereocenter.Scheme 2. Gram-scale synthesis of sulfamidate-fused 1,3-oxazolidine 3 a and its further applications.
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