Asymmetric Cyclization/Nucleophilic Tandem Reaction of o-Alkynylacetophenone with (Diazomethyl)phosphonate for the Synthesis of Functional Isochromenes

Copper-Catalyzed Domino Phosphorylation/Cyclization of ortho-Alkynylketones for Accessing Phosphorylated 1H-Isochromenes

An effective and economical copper-catalyzed approach for the synthesis of phosphorylated 1H-isochromenes is reported. This method is the first example of focus on ketone phosphonylation to establish a C-P bond and 6-endo-dig cyclization to construct a C-O bond between aryl- and alkyl-substituted alkynylketones and H-phosphinate esters, H-phosphites, and H-phosphine oxides, resulting in chemo- and regioselective phosphorylated 1H-isochromenes with moderate to excellent yields under smooth reaction conditions.

A chiral hydrogen atom abstraction catalyst for the enantioselective epimerization of meso-diols

Hydrogen atom abstraction is an important elementary chemical process but is very difficult to carry out enantioselectively. We have developed catalysts, readily derived from the Cinchona alkaloid family of natural products, which can achieve this by virtue of their chiral amine structure. The catalyst, following single-electron oxidation, desymmetrizes meso-diols by selectively abstracting a hydrogen atom from one carbon center, which then regains a hydrogen atom by abstraction from a thiol. This results in an enantioselective epimerization process, forming the chiral diastereomer with high enantiomeric excess. Cyclic and acyclic 1,2-diols are compatible, as are acyclic 1,3-diols. Additionally, we demonstrate the viability of combining our approach with carbon-carbon bond formation in Giese addition. Given the increasing number of synthetic methods involving hydrogen atom transfer steps, we anticipate that this work will have a broad impact in the field of enantioselective radical chemistry.

Transition Metal-Catalyzed Enantioselective Synthesis of Chiral Five- and Six-Membered Benzo O-heterocycles

Enantiomerically enriched five- and six-membered benzo oxygen heterocycles are privileged architectures in functional organic molecules. Over the last several years, many effective methods have been established to access these compounds. However, comprehensive documents cover updated methodologies still in highly demand. In this review, recent transition metal catalyzed transformations lead to chiral five- and six-membered benzo oxygen heterocycles are presented. The mechanism and chirality transfer or control processes are also discussed in details.

Ag(I)-catalyzed cyclization of o-alkynylacetophenones facilitated through acetal formation: synthesis of C3-naphthyl indole derivatives

A mild method for an efficient synthesis of C3-naphthyl indoles from o-alkynylacetophenones has been developed. This Ag-catalyzed transformation is assisted by the acetal formed under the reaction condition employing trimethyl orthoformate (TMOF). The role of acetal in promoting the reaction under ambient conditions has been established with control experiments. A range of C3-naphthyl indole derivatives have been synthesized in moderate to very good yields.

Asymmetric Addition of α-Diazomethylphosphonate to Alkylideneindolenine Catalyzed by a Trifunctional BINAP-Based Monophosphonium Salt

A series of trifunctional BINAP-based monophosphonium phase-transfer catalysts were developed and used in the asymmetric addition of α-diazomethylphosphonates to vinylogous imines formed in situ from sulfonylindoles. This methodology tolerates a broad scope of 2-unsubstituted sulfonyl indoles, which have seldom achieved high enantioselectivities in similar asymmetric reactions with other nucleophiles. Chiral 3-sec-alkyl-substituted indoles containing α-diazophosphonate were afforded in up to 99% yield and 95% ee.

Addition of benzyl ethers to alkynes: a metal-free synthesis of 1H-isochromenes

Bromotrimethylsilane (TMSBr)-promoted intramolecular cyclization of (o-arylethynyl)benzyl ethers to form 1H-isochromenes at room temperature is reported. Further studies indicated that vinyl carbocations are the reaction intermediates which are stabilized by the conjugated aryl groups. Thus, O-addition of benzyl ethers/tetrahydropyrans to alkynes was achieved under metal-free, acidic conditions. These reaction conditions were compatible with an alkynyl Prins reaction; therefore, 1H-isochromenes were produced directly from alkynyl benzaldehydes and alkynyl alcohols using a one-pot procedure.

Catalytic Asymmetric Tandem Reaction of o-Alkynylbenzaldehydes, Amines, and Diazo Compounds

An efficient asymmetric tandem reaction of o-alkynylbenzaldehydes, amines, and diazo compounds catalyzed by chiral silver imidodiphosphate has been established. Chiral 1,2-dihydroisoquinoline analogues have a tertiary stereocenter at the C1 position, and substituents at the C3 position are available with up to 97% yields and 98% ee. These products can be elaborated into the corresponding β-aminophosphonates or PARP1-inhibitor analogues.

Organocatalytic Asymmetric Multicomponent Cascade Reaction for the Synthesis of Contiguously Substituted Tetrahydronaphthols

Isobenzopyrylium ions are unique, highly reactive, aromatic intermediates which are largely unexplored in asymmetric catalysis despite their high potential synthetic utility. In this study, an organocatalytic asymmetric multicomponent cascade via dienamine catalysis, involving a cycloaddition, a nucleophilic addition, and a ring-opening reaction, is disclosed. The reaction furnishes chiral tetrahydronaphthols containing four contiguous stereocenters in good to high yield, high diastereoselectivity (up to >20:1), and excellent enantioselectivity (93-98% ee). The obtained products are important synthetic intermediates, and it is demonstrated that they can be used for the generation of frameworks such as octahydrobenzo[h]isoquinoline and [2.2.2]octane scaffolds. Furthermore, mechanistic experiments involving oxygen-18-labeling studies and density functional theory calculations provide a vivid picture of the reaction mechanism. Finally, the bioactivity of 16 representative tetrahydronaphthol compounds has been evaluated in U-2OS cancer cells with some compounds showing a unique profile and a clear morphological change.

Synthesis of 2-Aryl Acetophenones via Hydrobromination and Oxy-isomerization of (o-Arylethynyl)benzyl Alcohols

Hydrobromination and oxy-isomerization of (o-arylethynyl)benzyl alcohols to yield brominated aryl ketones were achieved with bromotrimethylsilane. The substrate scope suggested that vinyl carbocations, stabilized by the conjugated aryl groups, are the reaction intermediates. 1H-Isochromene was also detected by ¹H NMR, and an isolated 1H-isochromene was converted to the product when retreated with TMSBr. The formation of 1H-isochromene is equivalent to a 6-endo-dig cyclization and contrasts with the corresponding reactions under basic conditions, in which the 5-exo-dig process dominated.