Phosphine-Catalyzed Enantioselective [4 + 2] Cycloaddition–Semipinacol-Type-Rearrangement Reaction of Morita–Baylis–Hillman Carbonates

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

The stereoselective conversion of epimerized alkoxyl phosphine-borane to P,C, axial-stereogenic tertiary phosphine via cleavage of P-O bond

The P-O bond of epimerized alkoxyl phosphine-borane was cleaved by naphthalene-lithium, to form two diastereomers of P-anions in a ratio of 86 : 14, which was then converted to secondary phosphine-borane via acidification, and to tertiary phosphines with alkyl halides with enhanced 96 : 4 dr. The isolated tertiary phosphine containing hydroxyl (in >99 : 1 dr) was converted to multi-stereogenic tertiary phosphines via O-alkylation with alkylene dihalides.

Cleavage of Aromatic C-O Bonds via Intramolecular SNAr Reaction and Preparation of P,C,Axial-Stereogenic Menthyl Phosphine Derivatives

Phosphine ligands with up to six chiral sites were prepared, starting from 2-phenylphenol, via O- and P-alkylation, cyclization, and coupling. The chirality was transferred from (L)-menthyl to phosphorus, α-carbon, and axis, to achieve excellent diastereoselectivities. During an intramolecular S_NAr reaction with alkoxyl as the leaving groups, the C-O bond was converted to a C-C bond. Both phosphine boranes and oxides could be used for the conversions, affording a series of cyclic phosphines.

Insights into Lewis base-catalyzed chemoselective [3 + 2] and [3 + 4] annulation reactions of MBH carbonates

The chemoselectivity of Lewis base-catalyzed [3 + 2] and [3 + 4] annulation reactions of MBH carbonates can be predicted using FMO overlap analysis.

A theoretical review for novel Lewis base amine/imine-catalyzed reactions

Recent advances in computational investigations of Lewis base amine/imine-catalyzed reactions have been systematically summarized and reviewed for the first time.

Metal-free [3+3] benzannulation of 1-indanylidene-malononitrile with Morita–Baylis–Hillman carbonates: direct access to functionalized fluorene and fluorenone derivatives

An efficient [3+3] benzannulation of Morita–Baylis–Hillman carbonates with 1-indanylidenemalononitrile was achieved selectively delivering a wide range of functional fluorene or fluorenone compounds in high yields (up to 86% yields).

Chemoselective and Highly Rate Accelerated Intramolecular Aza-Morita-Baylis-Hillman Reaction

Despite being a very useful C-C bond forming and highly applicative reaction, Morita-Baylis-Hillman (MBH) reaction has been limited by its excessive slow reaction rate, including its intramolecular version. In certain cases, reaction time may even go to weeks and months. A highly chemoselective and rate accelerated intramolecular MBH reaction of just 15 min has been developed. The product dihydroquinoline, being unstable, was converted to an important quinoline framework. In some cases IMBH adducts were isolable, thus confirming the reaction path. Control experiments toward mechanism investigation have been carried out. Use of sodium sulfide has emerged as a rate accelerating catalyst in DMF-EtOH solvent system. Reaction intermediate for IMBH pathway was isolated and characterized. Other aspects such as the application of IMBH adduct for Michael addition and amidation have also been carried out.

Organophosphine-Catalyzed [4C+X] Annulations

In recent years, there have been extraordinary developments of organophosphine-catalyzed reactions. This includes progress in the area of [4C+X] annulations, which are of particular interest due to their potential for the rapid construction of 5–8-membered cyclic products. In this short overview, we summarize the remarkable progress, emphasizing reaction mechanisms and key intermediates involved in the processes. The discussion is classified according to the type of electrophilic reactants that acted as C₄ synthons in the annulation process, in the order of α-alkyl allenoates, γ-alkyl allenoates, α-methyl allene ketones, β′-OAc allenoate, δ-OAc allenoate, activated dienes and cyclobutenones.