Tungsten-Promoted [3+2]- and [3+3]-Cycloaddition of Epoxides with Alkynes. A Facile Enantiospecific Synthesis of Bicyclic Lactones

Transition Metal Vinylidene- and Allenylidene-Mediated Catalysis in Organic Synthesis

“…The resulting vinylidene 68 undergoes cyclization with the intramolecular alcohol and elimination to give Fischer carbene 70 , which participates in an array of reactions such as Grignard addition and hydrolysis . In addition to aldehydes, other electrophiles can be applied in initial C–C bond-forming step such as acetals, oxiranes, , aziridines, and N -acyl iminium ions . Nitrogen nucleophiles, instead of alcohols, can also trap metal vinylidene intermediates such as 68 .…”

Stereoselective Synthesis of Bicyclic Lactones Via Annelation Protocol

“…(5%) dilute hydrochloric acid (4 d rops) was added and the organic layer was extracted with ether (2 x 10 mL), dried over MgSO 4 To a stirred solution of 1,3-cyclopentanedione (279) (5 g, 0.05 mmo l, 1.00 equiv) in acetonitrile (80 mL) at 0 o C was added triethylamine (7.6 g, 0.07 mmo l, 1.30 equiv), and the solution was stirred for 10 min at roo m temperature. Methyl bromoacetate (9.9 g, 0.07 mmol, 1.30 equiv) was then added and stirring was continued over night by which time TLC revealed a new spot.…”

“…The co mbined organic layers were washed with sat. NaHCO 3 solution (2 x15 mL), brine (2 x 15 mL), dried over MgSO 4 and concentrated in vacuo. The residue was purified by colu mn chromatography on silica gel using a solvent gradient hexane : ethyl acetate fro m (4:1) to afford the title compound as a white powder (6.6 g, 78%); m. To a stirred solution of Wilkinsons catalyst (RhPPh 3 Cl) (236.00 mg, 0.589 mmo l, 0.5 equiv) in anhydrous THF (7 mL) under N2 cooled to -20 o C was added to methyl 2-(2-hydroxy -5-o xocyclopent-1-enyl)acetate (283) (200.0 mg, 1.18 mmol, 1.00 equiv ), followed by the addition of catecholborane (424.45 mg, 3.54 mmo l, 3.0 equiv).…”

“…The ether layer was followed by the addit ion of d ilute hydrochloric acid (5%) at 0 o C until the pH 2 was reached, by which t ime, TLC analysis showed a new product has been formed. The aqueous layer was extracted with ether (4 x 10 mL), the extract dried over MgSO 4 and concentrated in vacuo. Colu mn chro matography on silica, eluting with hexane : ethyl acetate gave the product as a colourless oil (122 mg , 73%); υmax (thin film/cm …”

“…In particu lar, the γ-butyrolactone mo iety is a recurrent feature of many naturally occurring substances examp les are brasoside and littoralissone. 1,2 The synthetic approaches to th is b icyclic lactones have been imaginative and numerous, [3][4][5][6][7][8] there is a continued demand fo r efficien t methods fo r the assemb ling o f these key co mp o u n d s wh ich g iv e es p ec ia lly h ig h lev e ls o f stereoselectivity. In this report, it is reported some of our preliminary resu lts in the estab lish ment o f an effect ive met h odo logy fo r th e const ruct io n o f t hes e impo rtant compounds.…”