Triethylamine-Promoted Henry Reaction/Elimination of HNO2/Cyclization Sequence of Functionalized Nitroalkanes and 2-Oxoaldehydes: Diversity-Oriented Synthesis of Oxacycles

The triethylamine-promoted cascade Henry reaction/elimination of HNO₂/cyclization reaction of 2-oxoaldehydes with nitroalkanes bearing various remote functionalities is described. Both chiral and achiral nitroalkanes were applicable to this protocol, leading to a variety of oxacycles, such as chromenes, chromanes, cyclic hemiacetals, and polycyclic acetals. An unexpected regioselective photooxygenation occurred without sensitizer during derivatization to convert a derived diene product into a dioxetane by reaction with singlet oxygen, which provided chromen-2-one and benzaldehyde after fragmentation.

Synthesis and antiproliferative activity of sulfa-Michael adducts and thiochromenes derived from carbohydrates

The synthesis of new carbohydrate-derived 3-nitro-2H-thiochromenes with potential antiproliferative activity is described.

Recent advancements on the use of 2-methyltetrahydrofuran in organometallic chemistry

ABSTRACT

Since the introduction of 2-methyltetrahydrofuran as an useful alternative to the classical tetrahydrofuran, there has been a continuous interest in the synthetic community operating at academic and industrial towards it. In particular, the much higher stability that basic organometallic reagents display in 2-methyltetrahydrofuran makes it suitable for processes involving such sensitive species including asymmetric transformations. The easy formation of an azeotropic mixture with water, the substantial immiscibility with water, and the fact it derives from natural sources (corncobs or bagasse), allow to consider it in agreement with the Anastas' Geen Chemistry principles. In this minireview, selected examples of its employment in organometallic transformations ranging from carbanions to radical and transition metal-catalyzed processes are provided.

GRAPHICAL ABSTRACT

Sulfonyl Azoles in the Synthesis of 3-Functionalized Azole Derivatives

Sulfonyl indoles, as well as related azolyl derivatives, have been recently introduced in synthesis as stable precursors of reactive indolenine intermediates. This personal account reports on the discovery of sulfonyl azoles and their practical utilization in many synthetic processes for the preparation of functionalized 3-substituted indoles, indazoles, and pyrroles. The indolenine intermediates obtained by treatment of sulfonyl azoles with Brønsted bases or Lewis acids can be considered as vinylogous imino derivatives that can be made to react with different nucleophilic reagents. These include organometallic reagents, reducing agents, stabilized carbanions, and heteronucleophiles. The controlled and mild conditions for the generation of indolenines from sulfonyl azoles make these substrates particularly useful in asymmetric synthesis, exploiting organo- or metal-catalyzed processes. Although less exploited, sulfonyl indoles can also be involved in photochemical processes for the preparation of polycyclic derivatives.

Reaction control in heterogeneous catalysis using montmorillonite: switching between acid-catalysed and red-ox processes

For a montmorillonite clay modified with a super-acid (CF₃SO₃H), two different modes of behaviour can take place simply by a judicious choice of reaction conditions.