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Optically active α-aminoboronic acids, find widespread application in medicinal chemistry. . Herein, we present a straightforward synthetic strategy based on the enantioselective cross-coupling of readily available racemic α-chloro boronates with carbamates using an earth-abundant copper catalyst with a commercial chiral diamine and a diaryl phosphine as the ligands. These reaction conditions originated from a mechanistic study of a photoinduced system. Mechanistic investigations support that product formation occurs via kinetic resolution of the racemic α-chloro boronate. Moreover, the diaryl phosphine is alkylated by the electrophile under the reaction conditions forming α-phosphino boronates that act as the active ligand during catalysis.

Transition-metal catalysis of substitution reactions of alkyl electrophiles by nitrogen nucleophiles is beginning to emerge as a powerful strategy for synthesizing higher-order amines, as well as controlling their stereochemistry. Herein, we report that a readily accessible chiral copper catalyst (commercially available components) can achieve the photoinduced, enantioconvergent coupling of a variety of racemic tertiary alkyl electrophiles with aniline nucleophiles to generate a new C–N bond with good ee at the fully substituted stereocenter of the product; whereas this photoinduced, copper-catalyzed coupling proceeds at −78 °C, in the a bsence of light and catalyst, virtually no C–N bond formation is observed even upon heating to 80 °C. The mechanism of this new catalytic enantioconvergent substitution process has been interrogated with the aid of a wide array of tools, including the independent synthesis of proposed intermediates and reactivity studies, spectroscopic investigations featuring photophysical and EPR data, and DFT calculations. These studies led to the identification of three copper-based intermediates in the proposed catalytic cycle, including a chiral three-coordinate formally copper(II)–anilido (DFT analysis points to its formulation as a copper(I)–anilidyl radical) complex that serves as a persistent radical that couples with a tertiary organic radical to generate the desired C–N bond with good enantioselectivity.

The shape reconstruction of a 3D object from its 2D crosssections is important for reproducing it by NC machining or rapid prototyping. In this paper, we present a method of surface approximation to cross-sections with multiple branching problems. In this method, we first decompose each multiple branching problem into a set of single branching problems by providing a set of intermediate contours using distance maps. For each single branching region, a procedure then performs the skinning of contour curves represented by cubic B-spline curves on a common knot vector, each of which is fitted to its contour points within a given accuracy. In order to acquire a more compact representation for the surface, the method includes an algorithm for reducing the number of knots in the common knot vector. The approximation surface to the crosssections is represented by a set of bicubic B-spline surfaces. This method provides a smooth surface model, yet realises efficient data reduction.