Aufbau von Heterocyclen durch [4 + 2]-Cycloaddition vonÜbergangsmetall-koordinierten Heteroolefinen mit Butadienen: zur Regioselektivität der Cycloaddition

Abstract

Abstract The pentacarbonyl(thioaldehyde), -(selenoaldehyde), and -(selenoketone) complexes (CO) 5M[X C(Ph)R] (I) (M = Cr: X = S, R = H (a); M = W: X = S, R = H (b); X = Xe, R = H (c); X = Se, R = Ph (d)) react with 2,3-dimethyl-1,3-butadiene by [4 + 2]-cycloaddition to give the metal-coordinated thia- and selenacycles, ( CO ) 5 M [ XC ( Ph ) RC H 2 CMe=CMeC ︹ H 2 ] (IIIa–d). The structure of IIId was established by an X-ray diffraction study. The reactions of Ia with 2-methyl-1,3-butadien (IV) and of Ia and Ib with trans-penta-1,3-diene (VI) are regioselective. The cycloaddition of IV to Ia yields the two isomers ( CO ) 5 Cr [ SC ( Ph ) HC H 2 CH = CMeC H 2 ︹ ] and ( CO ) 5 Cr [ SC ( Ph ) HC H 2 CMe = CHC H 2 ︹ ] , in a ratio of more than 9/55. The reaction of VI with Ia or Ib gives ( CO ) 5 M [ S ( Ph ) HC H 2 CH = CHC ︹ ( Me ) H ] or ( CO ) 5 M [ S ( Ph ) HC ( M e ) HCH = CHC ︹ H 2 ] in the ratio 2.4/1 (M = Cr) or 3/1 (M = W), respectively. The thiacycle can be cleaved from the metal intact by oxidation of IIIa with (NH 4) 2[Ce(NO 3) 6] in acetone.