Synthesis of Five-, Six-, and Seven-Membered Heterocycles by Intramolecular Ring Opening Reactions of 3-Oxetanol Derivatives

Chlorocyclization/cycloreversion of allylic alcohols to vinyl chlorides

Unprecedented chlorination of allylic alcohols: a simple mix-and-go procedure for the cyclization/cycloreversion of secondary and tertiary allylic alcohols with chloronium ions under mild conditions and practical access to remote carbonyl vinyl chlorides.

3-Aminooxetanes: versatile 1,3-amphoteric molecules for intermolecular annulation reactions

Despite the versatility of amphoteric molecules, stable and easily accessible ones are still limitedly known. As a result, the discovery of new amphoteric reactivity remains highly desirable. Herein we introduce 3-aminooxetanes as a new family of stable and readily available 1,3-amphoteric molecules and systematically demonstrated their amphoteric reactivity toward polarized π-systems in a diverse range of intermolecular [3 + 2] annulations. These reactions not only enrich the reactivity of oxetanes, but also provide convergent access to valuable heterocycles.

Tandem Suzuki Coupling/Intramolecular Oxetane Ring Opening to Form Polycyclic Ring Systems

A tandem one-pot reaction featuring a cross-coupling followed by an intramolecular oxetane ring opening by mild nucleophiles is reported. The overall transformation comprises a carbon-carbon bond formation along with a carbon-heteroatom bond construction providing diverse multicyclic ring systems with a pendant hydroxymethyl handle for further elaboration. This approach constitutes a convergent method for rapid access to various scaffolds. Furthermore, a comparison of computed low-energy conformers is presented to rationalize instances in which cyclization was not observed.

The Paternò–Büchi reaction – a comprehensive review

This review represents the most complete description of the scientific results obtained on a photochemical reaction described 110 years ago by an Italian scientist.

A Direct Synthesis of Highly Substituted π-Rich Aromatic Heterocycles from Oxetanes

The ubiquitous use of π-rich five-membered heterocycles has driven the development of new methods for their synthesis for more than a century. Here, we disclose a general and reliable reaction manifold for the construction of highly substituted heterocycles through a facile Lewis-acid-catalyzed oxetane rearrangement. Notably, this methodology employs a keto-oxetane motif as a 1,4-dicarbonyl surrogate, which can be synthesized using robust alkylation or alkenylation reactions, and thus obviates the need to access 1,4-dicarbonyl compounds via umpoled starting materials. We harnessed this reactivity to generate a broad range of substituted furans and pyrroles, and extended this methodology to produce benzo-fused versions thereof.

Total Synthesis and Configurational Assignment of Ascospiroketal A

The total synthesis of the marine fungus-derived natural product ascospiroketal is described. This concise synthesis relies on a unique Ag(I) -promoted tandem cascade cyclization that provides direct access to the correctly configured tricyclic core of the natural product from a linear precursor. The synthesis of candidate stereostructures of ascospiroketal A allowed for the confident assignment of both the relative and absolute stereochemistry of this unusual octaketide.

Pyrolysis Reactions of 3-Oxetanone

The pyrolysis products of gas-phase 3-oxetanone were identified via matrix-isolation Fourier transform infrared spectroscopy and photoionization mass spectrometry. Pyrolysis was conducted in a hyperthermal nozzle at temperatures from 100 to 1200 °C with the dissociation onset observed at ∼600 °C. The ring strain in the cyclic structure of 3-oxetanone causes the molecule to decompose at relatively low temperatures. Previously, only one dissociation channel, producing formaldehyde and ketene, was considered as significant in photolysis. This study presents the first experimental measurements of the thermal decomposition of 3-oxetanone demonstrating an additional dissociation channel that forms ethylene oxide and carbon monoxide. Major products include formaldehyde, ketene, carbon monoxide, ethylene oxide, ethylene, and methyl radical. The first four products stem from initial decomposition of 3-oxetanone, while the additional products, ethylene and methyl radical, are believed to be due to further reactions involving ethylene oxide.

Oxetane synthesis through the Paternò-Büchi reaction

The Paternò-Büchi reaction is a photochemical reaction between a carbonyl compound and an alkene to give the corresponding oxetane. In this review the mechanism of the reaction is discussed. On this basis the described use in the reaction with electron rich alkenes (enolethers, enol esters, enol silyl ethers, enanines, heterocyclic compounds has been reported. The stereochemical behavior of the reaction is particularly stressed. We pointed out the reported applications of this reaction to the synthesis of naturally occuring compounds.

Enantioselective intramolecular openings of oxetanes catalyzed by (salen)Co(III) complexes: access to enantioenriched tetrahydrofurans

The catalytic enantioselective intramolecular ring-opening of oxetanes with alcohols is catalyzed by (salen)Co(III) complexes. Either a monomeric or oligomeric catalyst can be used successfully in this transformation, providing 3-substituted tetrahydrofurans in both high yield and enantioselectivity. This methodology extends the range of electrophiles that can be activated toward highly enantioselective addition reactions by (salen)metal catalysts to an important new class.

Four-Membered Heterocycles with a Carbon−Heteroatom Exocyclic Double Bond at the 3-Position: Puckering Potential and Thermodynamic Properties

Despite the specific importance of four-membered heterocycles with a carbon-heteroatom double bond at the 3-position in organic and medicinal chemistry, little attention has been given up to now to theoretical computational studies on these molecules. However, the overall geometry, and degree of ring puckering especially, could significantly influence the reactivity and biological properties of these four-membered ring compounds. In this paper, focus is made on the influence of different substituents on the equilibrium geometry, ring puckering potential, and thermodynamic quantities. It was found that these properties are mainly affected by the heteroatom (oxygen, nitrogen, sulfur, phosphorus) contained in the ring skeleton. Moreover, the correct description of the puckering potential with the hindered rotor treatment leads to substantial corrections on the thermodynamic properties in the harmonic oscillator approximation.