Rauful Alam

Palladium-Catalyzed Synthesis and Isolation of Functionalized Allylboronic Acids: Selective, Direct Allylboration of Ketones†

Textbook revision: allylboronic acids, which are easily prepared from allylic alcohols, react readily and selectively with ketones without Lewis acid catalysts.

Synthesis of Adjacent Quaternary Stereocenters by Catalytic Asymmetric Allylboration

Allylboration of ketones with γ-disubstituted allylboronic acids is performed in the presence of chiral BINOL derivatives. The reaction is suitable for single-step creation of adjacent quaternary stereocenters with high selectivity. We show that, with an appropriate choice of the chiral catalyst and the stereoisomeric prenyl substrate, full control of the stereo- and enantioselectivity is possible in the reaction.

Stereoselective intermolecular allylic C-H trifluoroacetoxylation of functionalized alkenes.

Pd-catalyzed allylic C-H trifluoroacetoxylation of substituted alkenes was performed using PhI(OCOCF(3))(2) as the oxidant and acyloxy source. Trifluoroacetoxylation of monosubstituted cyclopentenes and cyclohexenes proceeds with excellent regio- and diastereoselectivity. Studies with one of the possible (η(3)-allyl)Pd(II) intermediates suggest that the reaction proceeds via stereoselective formation of Pd(IV) intermediates and subsequent stereo- and regioselective reductive elimination of the product.

Synergistic Visible-Light Photoredox/Nickel-Catalyzed Synthesis of Aliphatic Ketones via N–C Cleavage of Imides

An electrophilic, imide-based, visible-light-promoted photoredox/Ni-catalyzed cross-coupling reaction for the synthesis of aliphatic ketones has been developed. This protocol proceeds through N–C(O) bond activation, made possible through the lower activation energy for metal insertion into this bond due to delocalization of the lone pair of electrons on the nitrogen by electron-withdrawing groups. The operationally simple and mild cross-coupling reaction is performed at ambient temperature and exhibits tolerance for a variety of functional groups.

Transition‐Metal‐Free Borylation of Allylic and Propargylic Alcohols

Abstract The base‐catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1‐disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid–base adduct, [Hbase]+[MeO‐B2pin2]− favored the formation of 1,2,3‐triborylated species from the tertiary allylic alcohols and 1‐propargylic cyclohexanol at 90 °C.

Stereocontrol in Synthesis of Homoallylic Amines. Syn Selective Direct Allylation of Hydrazones with Allylboronic Acids

Allylboronic acids directly react with acyl hydrazones, affording homoallylic amine derivatives. The reaction proceeds with very high syn selectivity, which is the opposite of the stereochemistry observed for allylboration of imines. The reaction can be carried out with both aromatic and aliphatic acyl hydrazones. Based on our studies the excellent syn stereochemistry can be explained by chelation control of the acyl hydrazone and the B(OH)(2) moiety.

Catalytic Asymmetric Allylboration of Indoles and Dihydroisoquinolines with Allylboronic Acids: Stereodivergent Synthesis of up to Three Contiguous Stereocenters.

Abstract The catalytic asymmetric allylboration of cyclic imines with γ,γ‐disubstituted allylboronic acids provides products with adjacent stereocenters in high yield and stereoselectivity. Various electrophiles, including 3,4‐dihydroisoquinolines and indoles, were prenylated in a fully stereodivergent fashion by switching the E/Z geometry of the allylboronate and/or the enantiomer of the BINOL catalyst. 3‐Methylindole provided products with three adjacent stereocenters with high stereoselectivity in one synthetic operation.

Selective Formation of Adjacent Stereocenters by Allylboration of Ketones under Mild Neutral Conditions

Allylboronic acids readily react with a broad variety of ketones, affording homoallylic alcohols with adjacent quaternary and tertiary stereocenters. The reaction proceeds with very high anti stereoselectivity even if the substituents of the keto group have a similar size. α-Keto acids react with syn stereoselectivity probably due to the formation of acyl boronate intermediates. The allylation reactions proceed without added acids/bases under mild conditions. Because of this, many functionalities are tolerated even with in situ generated allylboronic acids.

Direct Synthesis of Secondary Benzylic Alcohols Enabled by Photoredox/Ni Dual-Catalyzed Cross-Coupling

An operationally simple, mild, redox-neutral method for the cross-coupling of α-hydroxyalkyltrifluoroborates is reported. Utilizing an Ir photocatalyst, α-hydroxyalkyl radicals are generated from the single-electron oxidation of the trifluoroborates, and these radicals are subsequently engaged in a nickel-catalyzed C-C bond-forming reaction with aryl halides. The process is highly selective, functional group tolerant, and step economical, which allows the direct synthesis of secondary benzylic alcohol motifs.