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A catalytic enantioselective reduction of α-trifluoromethylated imines by a BINOL-derived boro-phosphate employing catecholborane as hydride source has been developed. This method provides an efficient route to prepare synthetically useful chiral α-trifluoromethylated amines in high yields and with excellent enantioselectivities (up to 98% yield and 96% ee) under mild conditions.

Pinacolborane, catecholborane, triethylsilane, triphenylsilane, dimethylphenylsilane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, triethylgermane, triphenylgermane, and triphenylstannane deuterated at the heteroatom position have been catalytically prepared in 50–70% isolated yield, through H/D exchange between the D2 molecule and the respective boranes and hydrides of the group 14 elements, in the presence of the rhodium(I)-monohydride catalyst precursor RhH{κ3-P,O,P-[xant(PiPr2)2]} (xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene)., Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and RED2018-102387-T (AEI/FEDER, UE)), Gobierno de Aragón (Group E06_20R, project LMP148_18, and predoctoral contract to A.M.), FEDER, and the European Social Fund is acknowledged.

Without the addition of any additives and production of any small molecules, C3-borylated indoles and transfer hydrogenated indolines have been simultaneously achieved by a B(C6F5)3-catalyzed disproportionation reaction of a broad range of indoles with catecholborane. This catalyst system exhibits excellent catalytic performance for practical applications, such as easy scale-up under solvent-free conditions and long catalytic lifetime over ten sequential additions of starting materials. A combined mechanistic study, including isolation and characterization of key reaction intermediates, analysis of the disproportionation nature of the reaction, in situ NMR of the reaction, and analysis of detailed experimental data, has led to a possible reaction mechanism which illustrates pathways for the formation of both major products and byproducts. Understanding the reaction mechanism enables us to successfully suppress side reactions by choosing appropriate substrates and adjusting the amount of catecholborane nee...

The generation of 1-bromo and 1-chloroalkyl radicals from organoboranes has been investigated. The direct approach involving the hydroboration of halogenated alkenes is impeded by partial dehalogenation taking place during the hydroboration process. An indirect method involving the generation of B-(1-chloroalkyl)catecholborane by homologation of B-alkylcatecholborane with dichloromethyllithium was developed. A reaction sequence involving a hydroboration reaction, a Matteson homologation, and a radical allylation process has been performed as a one-pot process that takes advantage of three different reactivities of organoboron species. Starting from styrene derivatives, it was possible to prepare B-(1-chloro-2-arylpropyl)catecholboranes that are excellent precursors to 1-chloro-2-arylpropyl radicals. A concise approach for the synthesis of an optically active α-methylene-γ-lactone from p-chlorostyrene has been developed on the basis of a two-step sequence involving an enantioselective hydroboration-homologation-cyclization reaction followed by a hydrolysis-lactonization process.

A series of eremophilane sesquiterpene alcohols and hydrocarbons was prepared from the phytoalexin capsidiol (1) for mechanistic studies with epiaristolochene synthase and epiaristolochene dihydroxylase. Among them, 3-deoxycapsidiol (10) was obtained through selective derivatization and reductive cleavage of the equatorial 3 alpha hydroxyl group. Two novel isomers of aristolochene and eremophilene were accessed from the 1- and 3-deoxycapsidiol isomers. 4-Epieremophilene (17) was obtained by conjugate reduction of epiaristolochen-1-one tosylhydrazone with catecholborane followed by sulfinate elimination and diimide rearrangement. Epimerization of epiaristolochen-3-one (27a) at the C4 methyl followed by reductions led to the previously unknown aristolochene isomer, eremophila-9(10),11(12)-diene (30). Optical rotations and characteristic (1)H NMR data for the related eremophilenols and dienes are collected in Tables 1 and 2. Finally, bioassays were used to assess the antifungal potencies of capsidiol and its synthetic derivatives. The minimum inhibitory concentration for capsidiol (3-10 ng) was at least 1 order of magnitude lower than that of any of the derivatives and considerably lower than those previously reported for ketoconazole, nystatin, and propiconazole.

A variety of vinylic sulfides are stereospecifically synthesized by the catalytic hydroboration of thioacetylenes with catecholborane followed by cross-coupling of the resulting boron derivatives with organic halides. The use of the same palladium catalyst for both stages allows the whole transformation to be carried out in one flask. The synthetic utility of the method is demonstrated by the transformation of vinylic sulfides into diene, indole, and naphtho[b] furan derivatives

[reaction: see text] An efficient 10-step preparation from 4-methoxypyridine of (2R,3R,4R)-2-acetamido-3,4-dihydroxypiperidine ("XylNAc-isofagomine") in optically active form is described. Key steps include an enantioselective reduction with catecholborane/(S)-2-methyl-CBS-oxazaborolidine, and a stereoselective pseudo-glycosylation of lithium azide by a cyclic sulfite ester. The title compound showed a Ki = 21 microM when evaluated against the N-acetyl-beta-hexosaminidase from Streptomyces plicatus.

α,β-Unsaturated ketones which can readily adopt an s-cis conformation undergo conjugate reduction by catecholborane at room temperature. α,β-Unsaturated imides, esters, and amides are unreactive under the same conditions. However, catalytic quantities of Rh(PPh 3 ) 3 Cl greatly accelerate the 1,4-addition process, effecting conjugate reduction of these substrates by catecholborane at -20°C. The resulting boron enolates may be reacted with electrophiles to provide functionalized products

The stereoselective reduction of acyclic β-hydroxy ketones to syn 1,3-diols may be achieved with the mild reducing agent catecholborane. In certain instances reaction stereoselectivity may be enhanced through rhodium (I) catalysis

The purpose of this study was to investigate reducing agents which are as versatile as catecholborane but which can be more readily prepared. It is reported that bis(benzoyloxy)borane ((PhCO/sub 2/)/sub 2/BH) effectively reduces tosylhydrazones to the corresponding methylene derivatives. The results parallel those obtaining using catecholborane.