Regiodivergent reductive coupling of 2-substituted dienes to formaldehyde employing ruthenium or nickel catalyst: hydrohydroxymethylation via transfer hydrogenation

Abstract

The regioselective reductive coupling of paraformaldehyde to 2-substituted dienes at positions C1, C2 and C3 was achieved using metal catalysts based on nickel, cationic ruthenium and neutral ruthenium, respectively. Whilst C1 adducts predominate using dienes, silicon-or tin-substituted dienes exhibit C4 regioselectivity -the first time that this regioselectivity has been observed for the coupling of 2-substituted butadienes to aldehydes. Both nickel-and ruthenium-catalyzed processes avoid pyrophoric or mass intensive reducing agents, using paraformaldehyde or isopropanol, respectively. These couplings may be viewed as alternatives to diene hydroformylation, for which regioselective formation of constitutionally isomeric products has not yet been achieved.

Ruthenium-Catalyzed Transfer Hydrogenation for C–C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs

“…The collective data, including deuterium labeling experiments, 39,40 are consistent with the following mechanistic interpretation (Scheme 5). Hydroruthenation to form allylruthenium complex A is kinetically preferred.…”

“…For example, in 2-propanol mediated reductive couplings of 2-substituted dienes with paraformaldehyde (Scheme 4), 39–41 neutral ruthenium complexes favor coupling at the C3 position, 40 whereas ruthenium catalysts with greater cationic character favor coupling at the C2 position, resulting in formation of an all-carbon quaternary center. 39 An erosion in C2-regioselectivity is observed when cationic ruthenium catalysts are applied in reactions of higher carbonyl partners with 2-substituted dienes, as illustrated in couplings with ethanol (Scheme 4).…”

Regioselective Hydroacylation of 1,3-Dienes by Cobalt Catalysis

“…16 We hypothesize that Co(I) catalyst A would promote oxidative cyclization between aldehyde 1 and a 1,3-diene 2 . 17 The resulting cobaltacycle B exists in two η 1 forms: seven-membered cobaltacycle C and five-membered cobaltacycle C ′. 4,18,19 Depending on the substrate and ligand, cobaltacycle C or C ′ would undergo transformation by Path I or II, respectively.…”

Carbonylierungen von Alkenen mit CO‐Alternativen

“…[35] Es wurden Nickelkatalysatoren gefunden, die diese Kupplungen selektiv an der C1-Position durchführen, während 1,3-Diene mit 2-Silyl oder 2-Stannyl-Substituenten bevorzugt an der C4-Position reagieren (Schema 13). Bemerkenswerterweise berichteten 2013 Krische, Breit und Mitarbeiter über die reduktive Kupplung von Dienen mit Paraformaldehyd.…”