Monatshefle ftir Chemie 128, 697-700 (1997) Monatshefte fib"Chemie Chemical Monthlp © Springer-Verlag 1997 Printed in Austria On the Reaction Between Alkyl Isocyanides and 3-Benzylidene-2,4-pentanedione. A Convenient Synthetic Route to Densely Functionalized Furans I. Yavari*, A. Shaabani, and M. T. Maghsoodlou Chemistry Department, Tarbiat Modarres University, Tehran, Iran Summary. Alkyl isocyanides undergo a formal [1 ÷ 4] cycloaddition reaction with 3-benzylidene- 2,4-pentanedione yielding multiply functionalized furan ring systems in fairly high yields. The ]H NMR spectrum of 4-acety1-2-(N-benzylamino)-5-methyl-3-pnenylfuran shows an AB pattern for the benzylic methylene protons as a result of a restricted rotation about the bond between the acetyl group and the furan ring, thus giving rise to perpendicular disymmetric planes. Keywords. Alkyl isocyanides; [1 + 4] Cycloaddition; Conformational enantiomers; Functionalized furan. Eine einfache Synthese von hochfunktionalisierten Furanen durch Reaktion von Alkylisocyaniden mit 3-Benzyliden-2,4-pentadion Zusammenfassung. Alkylisocyanide gehen mit 3-Benzyliden-2,4-pentadion eine formale [1 + 4]- Cycloaddition ein, die in relativ hohen Ausbeuten zu mehrfach funktionalisierten Furansystemen ftihrt. Das 1H-NMR-Spektrum von 4-Acetyl-2-(N-benzylamino)-5-methyl-3-phenylfuranzeigt ftir die benzylischen Methylenprotonen ein AB-System, da das Molektil durch die sterische Hinderung der Rotation der Acetylgruppe asymmetrisch wird. Introduction Isocyanides [1-4] undergo a formal [1 + 4] cycloaddition reaction with conjugated electrophilic heterodienes. These reactions are of interest for the synthesis of func- tionalized heterocyclic five-membered ring systems. Cycloadditions of isocyanides with azadienes [5], diazadienes [6], N-acylimines [7], o~, fl-unsaturated esters [81, enones [9], and nitroalkenes [101 have been described. We report herein that alkyl isocyanides (1) undergo smoothly a formal [1 + 4] cycloaddition reaction with 3-benzytidene-2,4-pentanedione (2) [11], yielding N- substituted 4-acetyl-2-alkylamino-5-methyl-3-phenyl furans (4).