Controllable Synthesis of Two Isomers 4H-Chromene and 2,8-Dioxabicyclo[3.3.1]nonane Derivatives under Catalyst-Free Conditions

Brønsted Acid-Catalyzed Cascade Ring-Opening/Cyclization of 3-Ethoxy Cyclobutanones to Access 2,8-Dioxabicyclo[3.3.1]nonane Derivatives

A cascade ring opening of 3-ethoxy cyclobutanones followed by a double cyclization strategy has been developed via Brønsted acid catalysis. A range of 2,8-dioxabicyclo[3.3.1]nonanes are obtained from various substituted naphthols in a one-pot and open flux manner. Additionally, a 15-membered macrocycle has been synthesized by ring closing metathesis as a synthetic application.

Acid-Promoted Multicomponent Reaction To Synthesize 4-Phosphorylated 4H-Chromenes

An effective multicomponent reaction for the synthesis of 4-phosphorylated 4H-chromenes via a tandem phosphorylation/alkylation/cyclization/dehydration sequence with water as the only byproduct was developed. Extensive mechanistic investigations involving in situ NMR experiments, time control experiments, and in situ HRMS experiment allowed us to elucidate the order of each subreaction to arrive at a complete understanding of the underlying mechanism of this multicomponent reaction. Mechanistic data confirm that the reaction begins with a phospha-aldol-elimination, followed by addition of a ketone enolate, intermolecular alkylation, intramolecular cyclization, and dehydration under acidic conditions.

NBS-Promoted Synthesis of Thiocyanated Aminomaleimides and Site-Selective Intramolecular Cyclization Access to 1,4-Benzothiazepines via S-CN Bond Cleavage

A transition metal-free concise and efficient protocol for the synthesis of thiocyanated aminomaleimides and benzo[e][1,4]thiazepine derivatives has been developed. The method involves an initial α-C-H thiocyanation of aminomaleimides with KSCN and TEMPO-mediated tandem S-CN bond cleavage/intramolecular cyclization substitution processes, which enables the formation of seven-membered S/N-heterocycles. This synthetic strategy provides a reliable method for the synthesis of biologically interesting benzo[e][1,4]thiazepine derivatives by using KSCN as sulfur sources as well as expands the application of enaminones thiocyanation reactions in heterocycles synthesis.

Total Synthesis of (+)-Peniciketal B

An efficient synthesis of (+)-peniciketal B has been accomplished in 15 steps from the commercially available materials atraric acid, acryloyl chloride, and (+)-homoallylic alcohol. A convergent synthetic approach that is quite concise for constructing either "hemisphere" of (+)-peniciketal B with a common intermediate is employed that relies on a cascade intermolecular FeCl3-mediated "inner sphere" Michael-type reaction/double cyclization of an α,β-unsaturated ketone and substituted phenol to build the benzo-fused 2,8-dioxabicyclo[3.3.1]nonane with excellent diastereoselectivity. The generality of the transformation was also demonstrated by the broad scope of substrates that would be potential candidates for natural product synthesis and medicinal chemistry. Benzannulated [6,6]spiroketal was installed by a late-stage acid-catalyzed spiroketalization.

Tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides for the synthesis of 4-phosphorylated 4H-chromenes

A Hg(OTf)2-catalyzed tandem phospha-Michael addition/cyclization/dehydration of 2-hydroxychalcones with H-phosphine oxides is presented. This protocol provides a new and supplementary approach for the preparation of 4-phosphorylated 4H-chromenes in good yields (up to 99%). In addition, this domino reaction allows the successful construction of two new C-P and C-O bonds in a one-pot operation.