Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon−boron bond into a carbon−X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row dblock transition metals have become increasingly widely used as catalysts for the formation of a carbon−boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon−boron bonds.
A new palladium-catalyzed highly regioselective allylic C-H amination of alkenes with NFSI in the presence of a catalytic amount of water was developed and successfully expanded to Selectfluor-mediated palladium-catalyzed aminations of alkenes with N-tosylcarbamates in water at room temperature.
Alcohols are among the most abundant and readily available organic feedstocks in industrial processes. The direct catalytic functionalization of sp C-O bonds of alcohols remains the main challenge in this field. Here, we report a copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively. This protocol exhibits a broad reaction scope (40 examples) and high efficiency (up to 95% yield) under mild conditions, including for the preparation of secondary allylic boronates. Preliminarily mechanistic studies suggest that nucleophilic substitution is involved in this reaction.
This communication describes an efficient palladium pincer complex-catalyzed allylic C-H borylation of alkenes. The transformation exhibits high regio- and stereoselectivity with a variety of linear alkenes. A synthetically useful feature of this allylic C-H borylation method is that all allyl-Bpin products can be isolated in usually high yields. Preliminary mechanistic studies indicate that this C-H borylation reaction proceeds via Pd(IV) pincer complex intermediates.
An efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via Cu-catalyzed borylation under mild conditions is reported. In the presence of commercially available Cu(OAc) or Cu(acac) and Xantphos, the reaction affords the desired products in up to 92% yield with a broad substrate scope (43 examples). Isolation of an allenyl boronate as the reaction intermediate suggests that an insertion-elimination-type reaction, followed by borylcupration, is involved in the borylation of propargylic alcohols.
Organoboron compounds have found broad applications in the construction of novel CÀ C, CÀ O, and CÀ N bonds via transition metal-catalyzed reactions. The hydroboration of CÀ C multiple bonds is one of the most important methodologies to introduce the boron atom into the organic skeleton. Traditionally, boranes were employed in the hydroboration of enynes under transition metal-free conditions. When precious metal catalysts, such as palladium and rhodium were employed in the reactions, the scope of the hydroboration, as well as the regio-and stereoselectivity, was improved. The asymmetric hydroboration of enynes was also achieved via Pd-catalyzed reactions. In recent years, the non-precious 3d-metal catalysts, such as iron, cobalt, nickel and copper were employed in the hydroboration of enynes, especially in the enantiose-lective reactions. In this review, we have looked into the hydroboration of enynes as well as their mechanisms. Catalytic Hydroboration of Enynes 3.1. Precious Metal-Catalyzed Hydroboration of Enynes 3.2 Nonprecious Metal-Catalyzed Hydroboration of Enynes 4. Conclusion and Outlook
An efficient synthesis of tetramic acid derivatives was developed via intramolecular sp(3) C-H aminations of 1-acetyl N-aryl cyclopropane/cyclopentanecarboxamides in the presence of PhI(OPiv)(2) and CH(3)CH(2)COOH.
The synthesis of
allenyl-Bdan has been realized via the Cu(I)-catalyzed
borylation of propargylic alcohols. This methodology offers a facile
and efficient pathway toward allenyboronates with diverse functional
groups due to the simple access to the substrates. The substrates
bearing ester groups are well-tolerated in the synthesis of allenyl-Bdan
under the Lewis acidic conditions. The structures of two allenyl-Bdan
were further confirmed via single-crystal X-ray diffraction.
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