Effect of solvent polarity extremes on the coupling of cyclopropylcarbene-chromium complexes and alkynes: Synthesis of β-alkoxycyclopentadienones, 2-cyclopentene-1,3-diones, and cis 4,5-disubstituted cyclopentenones

Relative Asymmetric Induction in the Intramolecular Reaction between Alkynes and Cyclopropylcarbene−Chromium Complexes: Stereocontrolled Synthesis of Five-Membered Rings Fused to Oxygen Heterocycles

“…Rationalization of the Observed Stereochemistry. As noted in previous papers, ,2b the trans stereochemistry is anticipated for the carbocyclic ring, and this seems to be observed in all cases. With the exception of entries K and L, the heterocyclic ring in which the two substituents were either diequatorial or pseudodiequatorial was the major reaction product.…”

“…The intramolecular coupling of alkynes and cyclopropylcarbene−chromium complexes in aqueous solvents affords cyclopentenone rings fused to oxygen heterocycles in good-to-excellent yield (Scheme ) . Thermolysis of alkyne−carbene complex 1A initially produces a cyclopentadienone intermediate ( 2A ), which is reduced to the cyclopentenone vinylogous ester derivatives 3A under the reaction conditions. A new stereocenter is created at the asterisked carbon atom during the reduction process.…”

The [5+5] route to the phenanthrene skeleton

“…The only oxygenated system examined where the hydrophenanthrenone 55 was the major product was the fourth entry, which features an electron-deficient oxygen group. Although folklore holds that chromium carbene chemistry must be performed under highly air and moisture free conditions, we had earlier shown that considerable amounts of water do not interfere with the chromium carbene alkyne coupling event itself 36 When 19:1 dioxane:water was employed as the solvent for this reaction, the yield of 55 improved dramatically and crude reaction mixture NMRs appeared to be much cleaner. A subsequent effort to examine water as a reaction additive was undertaken (see ahead).…”

Synthesis and Chemoselective Reactivity of 3-Aminocyclopentadienones

“…While pleased with our ability to use 5 as the 4π component in cycloadditions, the experiments outlined in Scheme do not demonstrate the chemoselectivity of interest to us. With this in mind, we turned to the use of 5 in hetero-Diels−Alder cycloadditions with unsaturated aldehydes and ketones. , We were gratified to isolate adduct 8 in 82% yield when cyclopentadienone 5 was condensed with acrolein (eq 1).…”