Indenols, indenones and (arylcyclohexadienyl)Mn(CO)3 π-complexes from the thermally promoted reactions of alkynes with ortho-Mn(CO)4 aryl ketone, amide, ester and aldehyde derivatives

Three types of reactions with intramolecular five-membered ring compounds in organic synthesis

“…The thermally promoted reactions of the alkynes with an ortho-manganated acetophenone 24-3 give 1H-indene-1-ols 24-4 in a high yield. However, the reaction of the corresponding ortho-manganated derivatives of methyl 3,4,5-trimethoxybenzoate gives the indenone 24-5 in a high yield as shown in Scheme 4 [78].…”

Synthesis and alkyne-coupling chemistry of cyclomanganated 1- and 3-acetylindoles, 3-formylindole and analogues

“…Coupling of alkynes with orthomanganated aryl ketones to form 1H-inden-1-ols has been reported by us [1,2] and by Liebeskind's group [3], as have the corresponding alkyne-coupling reactions of orthomanganated N,N-diphenylhydrazones of acetophenone and benzaldehyde to form indenylhydrazines [4]. Cambie et al subsequently used these methods to prepare new steroidrelated compounds using substrates derived from the natural product podocarpic acid [5].…”

“…Because there is renewed interest in the synthesis of this class of polycyclic indole derivative [9] we report more general alkyne-coupling chemistry of 1, its Mn(CO) 2 [P(OMe) 3 ] 2 analogue 2, and the related 2-Mn(CO) 4 derivatives of 3-acetylindole and N-methyl-3-acetylindole (3,4). The report also includes the synthesis of the new cyclomanganated indole derivatives 2, 4, 5a…”

“…2-Hexyne, which gives acceptable indenol yields with cyclomanganated acetophenone [2], fails altogether to do so with 1 under thermal activation (entries 9-12).…”

“…Since replacement of two CO ligands by the poorer -accepting phosphite ligands will increase the Mn-CO bond order for the remaining CO ligands, this suggests that the reactivity of Me 3 NO with strongly coordinated CO is simply lost. It seems unlikely that alkyne would not coordinate if a metal coordination site were available as we have observed electron-deficient alkene (methyl acrylate) insertion in the complex of 3-acetyl-2,5-dimethylthiophene cyclometallated by Mn(CO) 2 [P(OMe) 3 ] 2 under thermal conditions [12].…”