Palladium-catalyzed [3C + 2C + 2C] cycloaddition of enynylidenecyclopropanes: efficient construction of fused 5-7-5 tricyclic systems

Abstract

We report a Pd-catalyzed intramolecular [3C + 2C + 2C] cycloaddition between alkylidenecyclopropanes, alkynes and alkenes. The method provides synthetically relevant 5-7-5 tricyclic structures, with good chemoselectivity and complete diastereoselectivity.

Aryl radical cyclization with alkyne followed by tandem carboxylation in methyl 4-tert-butylbenzoate-mediated electrochemical reduction of 2-(2-propynyloxy)bromobenzenes in the presence of carbon dioxide

“…The resulting aqueous solution was extracted with CH 2 Cl 2 (30 mL×2) and the combined organic layer was washed with H 2 O (100 mL×3).After drying over anhydrous MgSO 4 and evaporation of the solvent, column chromatography on silica gel (hexane/ether = 1/1) gave 4-allyloxy-2-butyn-1-ly methanesulfonate (2.45 g, 12 mmol, 83%). Spectral data were in good accordance with reported data 44. To a suspension of NaH (480 mg, 60% oil dispersion, 12 mmol, washed with hexane before use) in anhydrous THF (20 mL) was dropwise added tert-butyl N-(2-bromophenyl)carbamate (2.72 g, 10 mmol) at 0 °C under nitrogen atmosphere and then the reaction mixture was stirred at rt for 30 min.…”

Nickel‐Catalyzed [3+2+2] Cycloadditions between Alkynylidenecyclopropanes and Activated Alkenes

“…This transformation is kinetically favored over other alternative reaction pathways [10] owing to the stabilizing coordination of the carbonyl group of the ketone to the nickel moiety in the saddle point TS3 (and in intermediate iv). An alternative process, which would also eventually afford products of type 5, could involve the insertion of the methyl vinyl ketone into the C sp 3 ÀNi bond of iiib. However, the corresponding transition state for this process turned out to be 12.2 kcal mol À1 higher in energy, making that pathway very unlikely.…”

Transition‐Metal‐Catalyzed [3+2+2] Cycloaddition Reactions

“…Mascarenas and co‐workers have also reported Pd‐catalyzed intramolecular [3+2+2] cycloadditions of alkylidenecyclopropanes of type 81 (Scheme ). The method provides synthetically relevant 5–7–5 tricyclic structures, with good chemoselectivity and complete diastereoselectivity …”