Oxygenated monoterpenes as dipolarophiles for nitrilimine cycloadditions

A variety of naturally-occurring oxygenated monoterpenes, namely (S)-cis-verbenol, (1R)-(−)-myternol, (1S)-(−)-verbenone, (1R)-(−)-myternal, (S)-(−)-perillyl alcohol, and (S)-(−)-perillaldehyde have been submitted to nitrilimine cycloaddition. These processes were fully regio- and stereoselective for four dipolarophiles. In contrast, regioselective but non-stereoselective cycloadditions occurred in the case of two of the monoterpene derivatives. The configurations of the newly-formed stereocentres of the cycloadducts were assigned on the basis of NOE and NOESY experiments.     

Ketenimine and imine functions linked by an ethylene group. Intramolecular [4+2] cycloadditions leading to imidazo[1,2-b]isoquinolines

The intramolecular cyclization of imino-ketenimines where an ethylene or propylene chain is linking the nitrogen atoms of both functionalities is studied. The propylene tethered imino-ketenimines remain unchanged under thermal conditions, whereas their ethylene counterparts undergo a formal [4+2] cycloaddition, in which the ketenimine function acts as all-carbon diene and the imine as dienophile, to yield imidazo[1,2-b]isoquinolines. An X-ray crystal structure determination reveals that these cycloadducts incorporate an hydroxyl group at the benzylic carbon C10.     

An efficient three-step synthesis of cyclopenta[b]pyrans via 2-donor-substituted fischer ethenylcarbenechromium complexes

A wide range of cyclopenta[b]pyrans 4 has been synthesized in a one-pot reaction by treatment of different 2-donorsubstituted ethenylcarbenechromium complexes 2 with alkynes in THF in moderate to excellent yields (41-90 % for 14 out of 25 examples). The starting materials 2 are readily available in good to excellent yields (76-99 % for 25 out of 36 examples) by Michael addition of amines, alcohols and thiols, respectively, to the corresponding alkynylcarbenechromium complexes 1. Due to their 10 pi-electrons in a cross-conjugated bicyclic system, cyclopenta[b]pyrans have been termed pseudoazulenes, as they indeed have similar UV/Vis-spectroscopic properties.     

TREATMENT OF BERBERINE WITH INDIUM

Berberine, an important bioactive alkaloid, was treated with indium in aqueous ammonium chloride solution to produce tetrahydroberberine. This is the first report of the reduction of a natural quaternary alkaloid by applying indium.     

Selected Reactions on (R)Ph2PN?S3N3 Heterocycles: Exploration of chemical behavior and reactivity

Reactions of (R)Ph₂PN? S₃N₃ heterocycles with olefins such as norbornadiene, norbornene and dicyclopentadiene have yielded different results. Like Ph₃PN? S₃N₃, (R)Ph₂PN? S₃N₃ (R = C₄H₈N? , C₅H₁₀N? , C₆H₁₂N? , CH₃NC₄H₈N? and OC₄H₈N? ) compounds have given the cycloaddition products (R)Ph₂PN? S₃N₃ · C₇H₈ (yield 41 - 62%) with norbornadiene, while norbornene and dicyclopentadiene have not produced the corresponding adducts under identical conditions. With Ph₃PN? S₃N₃ both norbornene and dicyclopentadiene have given the ring expanded heterocycle, 1,5-[Ph₃PN]₂S₄N₄ in ca. 65% yield. The solution phase decomposition studies of (secondary amino) Ph₂PN? S₃N₃ derivatives have lead to the formation of (R)Ph₂PNH₂⁺X^?, while (primary amino) Ph₂PN? S₃N₃ has given Ph₂PS₂N₃ heterocycle in ca. 80% yield. Acid hydrolysis of (R)Ph₂PN? S₃N₃ derivatives has resulted in the isolation of Ph₂P(O)OH in all the cases, where R is an amino group.     

Photocycloaddition of (Z)-1,2-dichloroethylene to enantiopure 2(5H)-furanones: an efficient strategy for the diastereoselective synthesis of cyclobutane and cyclobutene derivatives

A highly stereoselective and efficient synthetic approach to cyclobutane and cyclobutene derivatives has been developed consisting of a [2+2] photochemical cycloaddition of chiral 2(5H)-furanones to (Z)-1,2-dichloroethylene followed by dihydrodehalogenation or dihaloelimination.     

Photodimerization of 4,6,4′-trimethylangelicin and 6,5-Dimethylangelicin

4,6,4'-Trimethylangelicin and 6,5'-dimethylangelicin form C4-cyclodimers when irradiated in water-ethanol solution. The former compound yields a pyrone-pyrone dimer similar to that formed by psoralens. 6,5'-Dimethylangelicin forms both pyrone-pyrone and pyrone-furan dimers; this unusual dimer has the cis-syn configuration.     

Investigation of Alkyne Regioselectivity in the Ni‐Catalyzed Benzannulation of Cyclobutenones

A Ni‐catalyzed benzannulation reaction of cyclobutenones and alkynes provides a rapid synthesis of heavily substituted phenols. The regioselectivity of this reaction can be modulated by variation of substituents on the alkyne. Though the incorporation of Lewis basic donors provides modest selectivities, the use of aryl substituents can provide high levels of regiocontrol. Finally, alkynylboronates derived from alkyl‐substituted acetylenes provide both high yields and regioselectivities. This study suggests that alkynes bearing one sp²‐ and one sp³‐based substituent can undergo benzannulation with high levels of regiocontrol whereby the sp³‐based group is incorporated ortho‐to the phenolic OH.