Donor–Acceptor Cyclopropanes as Three‐Carbon Components in a [4+3] Cycloaddition Reaction with 1,3‐Diphenylisobenzofuran

Abstract

Dienophiles with a difference: 2‐Aryl 1,1‐bis(alkoxycarbonyl) cyclopropanes undergo the title reaction under the catalysis of ytterbium triflate (Yb(OTf)3) in excellent yield (see scheme). Under mild reaction conditions, the major product is the less stable exo isomer. At higher temperatures, the endo isomer is obtained exclusively, as the exo cycloadduct decomposes through cycloreversion.

Donor‐Acceptor Cyclopropanes in the Synthesis of Carbocycles

“…In 2013, (3+8)‐cycloaddition with tropone derivatives has been reported . In 2008, we have described the first example of (3+4)‐cycloaddition of D‐A cyclopropanes with 1,3‐diene …”

“…This cycloaddition proceeded efficiently for a broad scope of substrates with diverse aryl, hetaryl and alkenyl substituents as donor groups. The optimal reaction time and temperature were found to depend on the nature of substituents in the starting cyclopropane . Cyclopropanes 1 with electron‐rich aromatic substituent reacted with 2 efficiently at room temperature, the conversion being faster for substrates with (het)aryl group having a better ability to stabilize carbocation.…”

Über bislang nicht beachtete Parallelen in der Reaktivität von Arinen und Donor‐Akzeptor‐Cyclopropanen

“…Analog zur Reaktivität von Arinen wurden D‐A‐Cyclopropane in einer (4+3)‐Anellierung mit 1,3‐Diphenylisofuranen zur Synthese des Cycloaddukts 34 in guten Ausbeuten eingesetzt. Zur besseren Umsetzung wurde Yb(OTf) 3 als Lewis‐Säure in CH 2 Cl 2 unter Rückfluss genutzt . Ähnliche Anellierungen von Arinen und D‐A‐Cyclopropanen mit Anthracen als Dienkomponente wurden ebenfalls realisiert .…”

Reactivity of Donor‐Acceptor Cyclopropanes with Saturated and Unsaturated Heterocyclic Compounds

“…Evanova et al . reported [4+3]‐cycloaddition reactions of DACs 32 with benzofuran derivative 33 under Lewis acid‐catalyzed reaction conditions (Scheme ).…”