Functionalized pyrroles from vinylaziridines and alkynes via rhodium-catalyzed domino ring-opening cyclization followed by CC bond migration

Rhodium(I)-catalyzed intermolecular cycloadditions of alkynes with vinyl aziridines bearing a conjugated carbonyl group in the olefin moiety followed by the double migration resulted in the formation of pyrrole derivatives in a one pot fashion.     

Design and synthesis of spirobiisoxazoline dibenzoquinone derivatives via [3 + 2] double 1,3-dipolar cycloaddition reaction

“A series of novel spirobiisoxazoline dibenzoquinone derivatives were synthesized starting from 2,5-dimethoxybenzaldehyde in a six-step synthetic sequence”. The key step [3?+?2] double 1,3-dipolar cycloaddition of oxime chloride with allenoate was performed under mild reaction conditions using sodium carbonate at ambient temperature. This is the first innovative synthesis of Spirobiisoxazoline Dibenzoquinone system where quinone ring is alkylated to isoxazoline moiety.     

Nickel-catalyzed [2 + 2] cycloaddition reaction using bisallenes

A nickel-catalyzed [2 + 2] cycloaddition of bisallenes has been described. Simple bisallenes are employed for the formation of “head to head” cycloadducts in the presence of Ni(0) with xantphos. The dienyl moiety in a product were applicable for various [4 + 2] cycloaddition reactions. Allene-allenamides under Ni-xantphos system gave the tricyclic compounds through sequential [2 + 2]–[4 + 2] cycloaddition reaction in highly stereoselective manner.     

Reduction vs. Addition: The Reaction of an Aluminyl Anion with 1,3,5,7‐Cyclooctatetraene

The potassium aluminyl complex K[Al(NON^Ar)] (NON=NON^Ar=[O(SiMe₂NAr)₂]^2?, Ar=2,6‐iPr₂C₆H₃) reacts with 1,3,5,7‐cyclooctatetraene (COT) to give K[Al(NON^Ar)(COT)]. The COT‐ligand is present in the asymmetric unit as a planar μ₂‐η²:η⁸‐bridge between Al and K, with additional K???π‐aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT]^2?. Addition of 18‐crown‐6 causes a rearrangement of the C₈‐carbocycle to form the isomeric 9‐aluminabicyclo[4.2.1]nona‐2,4,7‐triene anion.     

Solid‐State Synthesis of Two Different Polymers in a Single Crystal: A Miscible Polymer Blend from a Topochemical Reaction

The topochemical synthesis of a miscible polymer blend is described. The azide‐ and alkyne‐decorated tetrol 1 crystallizes as two different conformers. Both conformers exhibit self‐sorted head‐to‐tail alignment with proximally placed reacting groups such that topochemical polymerization yields two types of polymer chains, each containing only one type of conformer. The orientation of complementary reactive groups in one of the head‐to‐tail‐arranged conformers favors the formation of cis‐triazole linkages, and the other favors the trans‐triazole linkages. Crystals of 1 on heating gave a perfect polymer blend containing equal amounts of cis‐triazole‐linked and trans‐triazole‐linked polymers. As each conformer is H‐bonded to four conformers of the other kind, the polymerization yields a perfect polymer blend wherein each polymer chain is surrounded by chains of the other type. Thus, the molecular ordering in the prepolymerized state in a crystal is utilized to create a polymer blend.     

Copper(II)–acid catalyzed cyclopropanation of 1,3-dienamides by electrophilic activation of α-aryl diazoesters

Copper(II)–acid catalyzed cyclopropanation of electron-rich alkenes, such as 1,3-dienamides, with α-aryl diazoesters are described. The reaction could be performed without rare metal catalysts, excess substrate, or the need for the slow addition of the diazoesters.     

Molecular complexity from aromatics. Studies on synthesis of polycyclic system related to crotogoudin

Synthesis of tricyclic systems related to crotogoudin from a simple aromatic precursor has been described. Oxidative dearomatization, tandem retro-Diels–Alder/Diels–Alder reaction and ring-closing metathesis are the key features of our approach.     

One pot,three component 1,3 dipolar cycloaddition: Regio and diastereoselective synthesis of spiropyrrolidinyl indenoquinoxaline derivatives

A competent and highly discriminating one-pot synthesis of highly diversified novel functionalized indenoquinoxalone grafted spiropyrrolidine linked chromene-3-carbonitrile conjugates accumulating three pharmocophoric cores, heterocyclic indenoquinoxalone, pyrrolidines and chromene-3-carbonitrile in a single molecular framework by means of 1,3-dipolar cycloaddition reaction between indenoquinoxalone, proline/benzyl amine and chromene-3-carbonitrile in ethanol under classical and microwave conditions is described. The three component 1,3-dipolar cycloaddition reaction proceeds via in situ generation of azomethine ylides by the decarboxylative condensation of indenoquinoxalone with proline/benzyl amine and their selectivity towards the endo cyclic double bonds of dipolarophile (chromene-3-carbonitrile) leading to the formation of highly functionalised regio- and diastereoselective molecular hybrids. This methodology exemplifies the green chemistry protocol such as mild reaction conditions, high yields, one-pot procedure and operational simplicity.     

Cycloadditions between methyl (Z)-2-bromo-4,4,4-trifluoro-2-butenoate and various tosylacetamides: Synthesis of trifluoromethylated pyroglutamates and 2-pyridones derivatives

Cycloaddition reactions between methyl (Z)-2-bromo-4,4,4-trifluoro-2-butenoate and various 2-tosylacetamides are described. Various 2-tosylacetamides react with methyl (Z)-2-bromo-4,4,4-trifluoro-2-butenoate in the presence of NaH at room temperature in one step to form trifluoromethylated pyroglutamates as single diastereomers. However, employing the same reactants using t-BuOK as base at ?78?°C results in the formation of trifluoromethylated 2-pyridones. A ring-closure mechanism is proposed for the reaction.