Copper-Catalyzed Umpolung of Imines through Carbon-to-Nitrogen Boryl Migration

Abstract

We report a general strategy for the catalytic umpolung of imines, which was enabled by an unprecedented 1,2-boryl carbon-to-nitrogen migration. Based on the discovery of a rearrangement of an α-borylalkylamido copper intermediate to an α-borylaminoalkyl copper species through 1,2-migration of a boryl group from carbon to nitrogen and copper migration from nitrogen to carbon, we have developed a copper-catalyzed selective allylation of a wide range of aldimines and ketimines with allyl electrophiles in the presence of B2(pin)2 and LiOtBu. We expect this catalytic imine-umpolung strategy may derive useful methodologies for the synthesis of various functionalized amines.

Nucleophilic reactivity of the gold atom in a diarylborylgold(i) complex toward polar multiple bonds

“…The observation of a characteristic benzyl proton signal with a relatively downeld chemical shi (d H 5.72 ppm) and signals of the six methyl groups of the o-tolyl and Dip groups in the 1 H NMR spectrum of 7 supports the existence of a chiral center at the benzylic position in 7. Benzophenone also reacts with 2, furnishing a similar adduct (8), albeit with a more symmetrical structure, which is supported by 1 H NMR spectroscopy. The reaction of p-uorobenzoyl chloride with 2 results in the formation of p-uorobenzoylgold-chloroborane complex 9 via the formation of Au-C, O-B, and B-Cl bonds.…”

“…7 In the Cu-catalyzed allylation of imine in the presence of B 2 pin 2 and allyl bromide would also involve the nucleophilic attack of Bpin to form borylamido-Cu intermediate followed by a boryl migration (Scheme 1e). 8 exhibit strong Lewis acidity on the boron center. Although several theoretical studies on the properties of terminal TM-BH 2 (dihydroboryl) complexes have been published, 9 reports on their synthesis are not available, probably due to the almost complete lack of steric hindrance.…”

Snapshots of magnesium-centred diborane heterolysis by an outer sphere SN2 process

“…Although 17 BCN is stabilised by a significant interaction between the magnesium centre and one of the pinacolato oxygen atoms (2.08 Å), it is unobservable under the experimental conditions and, most likely as a result of its inherent ring strain, is transformed immediately to 17 BC via a negligible barrier [ TS(17 BCN -17 BC ) ] of 4.1 kcal mol –1 . Although a related nitrogen-to-carbon rearrangement has been implicated in the decomposition of PhCH 2 CH(Bpin)(NH 2 ) to PhCH 2 CH 2 NHBpin,75 to the best of our knowledge, the transformation of 17 BN to 17 BC provides the first documented example of a retro aza-bora-Brook rearrangement 76,77…”

Ligand‐Controlled Copper‐Catalyzed Regiodivergent Carbonylative Synthesis of α‐Amino Ketones and α‐Boryl Amides from Imines and Alkyl Iodides

“…Concerning the reaction pathway, based on the experimental results and related literatures, [1–4, 12–14, 18] a possible reaction pathway is proposed (Figure 2). Initially, LCu‐Bpin I , generated from CuCl, B 2 pin 2 and NaO t Bu, inserts into the C=N bond of imine to give α‐boryl amido‐copper complex II .…”

“…Initially, LCu‐Bpin I , generated from CuCl, B 2 pin 2 and NaO t Bu, inserts into the C=N bond of imine to give α‐boryl amido‐copper complex II . In the case of presenting electron‐deficient ligand, the N‐Cu bond is weaker and the copper specie II trend to occur intramolecular 1,2‐rearrangement to afford α‐amino alkylcopper complex III (Figure 2, left catalytic pathway) [18] . Afterwards, alkylcopper III reacts with alkyl iodide to generate copper complex IVa .…”