The
formation of arene C–N bonds directly from C–H
bonds is of great importance and there has been rapid recent development
of methods for achieving this through radical mechanisms, often involving
reactive
N
-centered radicals. A major challenge associated
with these advances is that of regiocontrol, with mixtures of regioisomeric
products obtained in most protocols, limiting broader utility. We
have designed a system that utilizes attractive noncovalent interactions
between an anionic substrate and an incoming radical cation in order
to guide the latter to the arene
ortho
position.
The anionic substrate takes the form of a sulfamate-protected aniline
and telescoped cleavage of the sulfamate group after amination leads
directly to
ortho
-phenylenediamines, key building
blocks for a range of medicinally relevant diazoles. Our method can
deliver both free amines and monoalkyl amines allowing access to unsymmetrical,
selectively monoalkylated benzimidazoles and benzotriazoles. As well
as providing concise access to valuable
ortho
-phenylenediamines,
this work demonstrates the potential for utilizing noncovalent interactions
to control positional selectivity in radical reactions.
Cyclic ketones bearing α‐quaternary stereocenters underwent efficient kinetic resolution using cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus. Lactones possessing tetrasubstituted stereocenters were obtained with high enantioselectivity (up to >99 % ee) and complete chemoselectivity. Preparative‐scale biotransformations were exploited in conjunction with a SmI2‐mediated cyclization process to access complex, enantiomerically enriched cycloheptan‐ and cycloctan‐1,4‐diols. In a parallel approach to structurally distinct products, enantiomerically enriched ketones from the resolution with an α‐quaternary stereocenter were used in a SmI2‐mediated cyclization process to give cyclobutanol products (up to >99 % ee).
Ortho-sulfonyl anilines are important building blocks for a range of applications. We report the discovery of an aromatic rearrangement reaction of O-(arenesulfonyl)hydroxylamines which leads directly to ortho-sulfonyl anilines through formation of a new CÀ N bond with excellent levels of regiocontrol for the ortho position(s) over all others. We establish that the rearrangement is proceeding through an intermolecular mechanism and propose that the regiocontrol observed is the result of attractive non-covalent interactions occurring during the CÀ N bond-forming step. Importantly, this method is complementary to classical aniline sulfonation in terms of the variously substituted regioisomers that can be obtained and it is also applicable to O-(benzylsulfonyl) hydroxylamines.
Scheme 1. A. BVMOs in the kinetic resolution of cyclic ketones:l ack of precedent for the resolution of substrates bearing a-quaternary stereocenters. B. An approach to complex, medium-sized cycloalkanolst hat exploits the synergy between ab iocatalytica nd achemical process. C. The biological importanceo fmolecules containing cycloheptanol and cyclooctanol motifs.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.
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