Gold Catalysis Enabling Furan-Fused Cyclobutenes as a Platform toward Cross Cycloadditions

Quinazoline-Derived Azomethine Imines as Substrates To Access Polycyclic Compounds

Quinazolines are essential structural constituents of many pharmaceuticals and bioactive natural products. Quinazoline-derived azomethine imines (QAIs) have emerged recently as valuable building blocks for the synthesis of various quinazoline derivatives. This Synopsis presents recent advances in (formal) cycloaddition reactions of QAIs for the synthesis of quinazoline-fused 5- to 8-membered heterocycles as well as three-dimensional compounds.

Sequential Dearomatization/Rearrangement of Quinazoline-Derived Azomethine Imines for the Synthesis of Nitrogen-Rich Three-Dimensional Cage-Like Molecules

A sequential dearomatization/rearrangement reaction between quinazoline-derived azomethine imines and crotonate sulfonium salts has been developed to provide a series of three-dimensional cage-like molecules. The reaction involves two dearomatizations, two cyclizations, and two C-C bond and three C-N bond formations in one step. The new transformation has a broad substrate scope, does not require any added reagents, and proceeds under room temperature in a short time. A mechanistic rationale for the sequential dearomatization/rearrangement is also presented. Furthermore, the synthetic compounds are evaluated for their glucose control effect. Compounds 3aa and 3aj were found to be hyperglycemic, which might be lead compounds for treating hypoglycemia.

Silver-Catalyzed Tandem Cycloisomerization/[5 + 2] Cycloaddition of 3-Cyclopropylideneprop-2-en-1-ones with Oxidopyrylium Ylides to Form Bibridged Benzocycloheptanones

Herein, we report a mild, one-pot method for silver-catalyzed tandem cycloisomerization/[5 + 2] cycloaddition reactions between readily accessible cyclopropyl-tethered allenyl ketones and benzopyranone-derived oxidopyrylium ylides. The reactions proceed via a cyclobutene-fused furan intermediate generated in situ by a cycloisomerization/1,2-carbene transfer/ring-expansion cascade. This method, which features an unprecedented formal [5 + 2] cycloaddition, delivers good to excellent yields of structurally complex bibridged benzocycloheptanones bearing a strained cyclobutane ring and an O-bridged ring.

Modular Synthesis of Tetrasubstituted Pyrroles via an Annulative Migration Reaction of Allenyl Ketones and p-Toluenesulfonylmethyl Isocyanide

The metal-free cyclization of allenyl ketones and p-toluenesulfonylmethyl isocyanide (TosMIC), promoted by Cs₂CO₃, provides a convenient access to tetrasubstituted pyrroles in which an acyl group undergoes 1,2-migration. This tandem Michael addition/annulative migration synthetic strategy is general and high-yielding for various substituted allenyl ketones. Moreover, a phosphoryl or ester moiety is also a suitable functionality to enable such migration.

Palladium-catalyzed hydroamination of vinylidenecyclopropane-diester with pyrroles and indoles: an approach to azaaromatic vinylcyclopropanes

A new method for the synthesis of azaaromatic vinylcyclopropanes (VCPs) has been disclosed in this paper by using pyrrole or indole derivatives as nucleophilic reagents to react with vinylidenecyclopropane-diesters (VDCP-diesters) in the presence of a Pd catalyst, a phosphine ligand and a base under mild conditions in up to 98% yield with a reasonable substrate scope. This reaction is one of the few examples of hydroamination at electron-rich allene's β-position. A plausible reaction mechanism has also been proposed through a zwitterionic π-propargyl N-palladium species according to the previous work and the obtained deuterium labeling experimental result.

Gold(I)-Catalyzed Heteroannulation of Salicylic Amides with Alkynes: Synthesis of 1,3-Benzoxazin-4-one Derivatives

Gold(I)-catalyzed heteroannulation affords the efficient and straightforward construction of heterocyclic compounds. Herein, we developed a gold(I)-catalyzed heteroannulation of salicylic amides with alkynes producing a broad range of 1,3-benzoxazin-4-ones. The utility of this protocol was highlighted by synthesizing variously substituted benzoxazinones containing quaternary carbon centers, showing a high functional group tolerance and excellent atom economy of the thus introduced reaction course.