O-Isocyanates as Uncharged 1,3-Dipole Equivalents in [3+2] Cycloadditions

Expedient cobalt-catalyzed stereospecific cascade C-N and C-O bond formation of styrene oxides with hydrazones

Cobalt-catalyzed cascade C-N and C-O bond formation of epoxides with hydrazones is described to furnish oxadiazines using air as an oxidant. The catalyst plays a dual role as a Lewis acid followed by a redox catalyst to accomplish the C-H/O-H cyclization. Optically active styrene oxide can be reacted enantiospecifically (>99% ee).

Asymmetric Decarboxylative [3+2] Cycloaddition for the Diastereo- and Enantioselective Synthesis of Spiro[2.4]heptanes via Cyclopropanation

Asymmetric cycloaddition reaction has emerged as one of the powful and reliable strategies for the construction of enantioenriched molecules, especially those with polycyclic frameworks. Herein, we report the asymmetric decarboxylative...

Multicomponent formation route to a new class of oxygen-based 1,3-dipoles and the modular synthesis of furans

A new class of phosphorus-containing 1,3-dipoles can be generated by the multicomponent reaction of aldehydes, acid chlorides and the phosphonite PhP(catechyl). These 1,3-dipoles are formally cyclic tautomers of simple Wittig-type ylides, where the angle strain and moderate nucleophilicity in the catechyl-phosphonite favor their cyclization and also direct 1,3-dipolar cycloaddition to afford single regioisomers of substituted products. Coupling the generation of the dipoles with 1,3-dipolar cycloaddition offers a unique, modular route to furans from combinations of available aldehydes, acid chlorides and alkynes with independent control of all four substituents.

Ynamides as Three-Atom Components in Cycloadditions: An Unexplored Chemical Reaction Space

While 1,3-dipolar cycloadditions have appeared to be a fertile area for research, as attested by the numerous synthetic transformations and resulting applications that have been developed during the past 60 years, the use of neutral three-atom components (TACs) in (3+2) cycloadditions remains comparatively sparse. Neutral TACs, however, have great synthetic potential given that their reaction with a π system can produce zwitterionic cycloadducts that may be manipulated for further chemistry. We report herein that ynamides, a class of carbon π systems that has seen wide interest over the last two decades, can be used as neutral TACs in thermally induced intramolecular (3+2) cycloaddition reactions with alkynes to yield a variety of functionalized pyrroles. The transformation is proposed to occur in a stepwise manner via the intermediacy of a pyrrolium ylide, from which the electron-withdrawing group on the nitrogen atom undergoes an intramolecular 1,2-shift to produce the neutral pyrrole. This work demonstrates a yet unexplored facet of ynamide reactivity with great potential in heterocyclic chemistry.

Synthesis and characterization of phosphorous(III) diisocyanate and triisocyanate

Two phosphorous(iii) isocyanates, ClP(NCO)2 and P(NCO)3 were isolated as neat substances and characterized with IR (gas-phase and Ne-matrix), Raman (solid), and 31P NMR spectroscopy. Their vibrational spectra were analyzed in terms of a single conformer with the aid of quantum chemical computations at the B3LYP/6-311+G(3df) level of theory. In line with the theoretically computed favorable syn-configuration of the NCO ligands with the sterically active lone-pair electrons on the central phosphorous atom (nP), low-temperature single-crystal X-ray diffraction (XRD) of solid ClP(NCO)2 reveals a Cs symmetric syn-configuration for both NCO ligands with weak CO (r = 2.9692(4) Å) van der Waals (vdW) interactions. In the binary isocyante P(NCO)3, all the three NCO ligands adopt similar syn-configuration with nP, leading to a propeller-shaped structure with slightly distorted C3v symmetry due to steric repulsion of the NCO ligands and the PO vdW interactions (r = 3.1901(1) Å) in the solid state.