Organische Synthesen mit Übergangsmetallkomplexen, 48. Methyl(thiocarben)‐ und Alkenyl(thiocarben)‐Chrom‐Komplexe: Darstellung und Reaktionen

Organic Syntheses via Transition Metal Complexes, 48. — Methyl Thiocarbene and Alkenyl Thiocarbene Chromium Complexes: Synthesis and Reactions Thiocarbene chromium complexes (CO)5CrC(SR1)R (4: R  Me, Ph; R1  c‐C6H11, CH2CHCH2, C2H5, C6H5) were readily obtained in up to 97% isolated yields from the corresponding ethoxycarbene chromium complexes 5a, b and thiols 6 in methanol in the presence of Na2CO3 as a catalyst. Reaction conditions, which lead to unfavorable side products, like thioacetals 8 and or thioenol ether 10, are discussed. Methyl thiocarbene complexes 4b–d undergo a facile aldol condensation with the aromatic aldehydes 14 or 16 to give alkenyl thiocarbene complexes 15b–d and 17, respectively. The CrC bonds of 15 prove to be reactive towards the insertion of isocyanides or oxygen. Thus, on addition of two equivalents of the isocyanide 18 to 15d, 1‐aza‐1,2,4‐pentatriene 20 is obtained. The oxidative decomposition of 15d on silica gel leads to the formation of thioester 25 and thioindene 26. Characteristic differences in the reactivity of thiocarbene complexes and ethoxycarbene complexes are discussed.