The Ru(II)‐Pheox catalyzed B−H bond insertion reactions of α‐methyl diazoesters with phosphine‐ and amine‐borane adducts were successfully developed. A unique α‐methyl diazoester (dinaphthylenyl diazopropionate) with triphenylphosphine‐borane afforded the highest enantioselectivity (up to 98 % ee). Moreover, a unique dinaphthylenyl diazophenylacetate was newly synthesized, leading to improved yield and enantioselectivity of the carbene transfer B−H insertion reaction.
The stereoselective synthesis of optically active cyclopropylsilanes from various allyl‐ and vinylsilanes with functionalized diazoesters was achieved in excellent yields (up to 99 %) and diastereo‐ (up to >99 : 1 d.r.) and enantioselectivities (up to 99 % ee) in the presence of Ru(II)‐Pheox catalysts. Among a series of Ru(II)‐Pheox catalysts, p‐MeO−Ru(II)‐Pheox was determined to be the best catalyst for cyclopropanation reactions of diazoesters with various allylsilanes. Also, methyl(diazoacetoxy)acetate afforded in significantly enhanced yields, diastereoselectivities, and enantioselectivities. The cyclopropanation reactions with vinylsilanes with methyl (diazoacetoxy)acetate proceeded with excellent diastereoselectivities (>99 : 1 d.r.). Moreover, cyclopropylsilane derivatives could be successfully transformed into beneficial building blocks for the synthesis of bioactive compounds, including an anti‐HIV drug and Imatinib‐7.
A reusable and highly enantioselective catalyst for the intramolecular cyclopropanation of various diazo ester and Weinreb amide derivatives was developed. The reactions catalyzed by a water-soluble Ru(II)-Amm-Pheox catalyst proceeded smoothly at room temperature, affording the corresponding bicyclic cyclopropane ring-fused lactones and lactams in high yields (up to 99%) with excellent enantioselectivities (up to 99% ee). After screening of various catalysts, the Ru(II)-Amm-Pheox complex having an ammonium group proved to be crucial for the intramolecular cyclopropanation reaction in a water/ether biphasic medium. The water-soluble catalyst could be reused at least six times with little loss in yield and enantioselectivity.
Over the years, numerous modifications to the structure of proline have been made in order to tune its effects on bioactive compounds. Notably, the introduction of a cyclopropane ring or a fluorine atom has produced interesting results. Herein, we describe the synthesis of a proline containing fluorocyclopropane. This modified amino acid was inserted into a tripeptide, whose conformation was studied by nuclear magnetic resonance and density functional theory calculations.
The first catalytic
asymmetric cyclopropanation of diazo oxime
ethers with olefins was developed. In the presence of a Ru(II)-Pheox
catalyst, various optically active cyclopropyl oxime derivatives were
obtained in high yields (up to 99%) with high enantioselectivities
(up to 98% ee). Furthermore, optically active cyclopropyl oxime ethers
could be successfully converted into the corresponding cyclopropyl
methylamine derivatives via metal hydride and Grignard reagent mediated
Beckmann rearrangement, which are potential candidates for the assessment
of biological and pharmaceutical activities.
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