Kinetically Controlled Stereoselective Access to Branched 1,3-Dienes by Ru-Catalyzed Remote Conjugative Isomerization

Abstract

A Ru-catalyzed conjugative isomerization of remote alkenes that affords branched 1,3-dienes is described. These kinetic products are obtained in high yields, good levels of regiocontrol, and high stereoselectivity. A broad range of functional groups and heterocycles are compatible with the mild reaction conditions, and isomerization is sustained over long distances. Control experiments support a metal-hydride mechanism consisting of iterative migratory insertions/β-H eliminations, which is initiated preferentially at the terminal olefinic site. Two one-pot multimetallic selective catalytic sequences using [Ru/Cu] and [Ru/Rh] combinations have been developed to illustrate the synthetic potential of the process.

Switching between Hydrogenation and Olefin Transposition Catalysis via Silencing NH Cooperativity in Mn(I) Pincer Complexes

“…3 Alternatively, transposition of pre-existing olefins offers a powerful and atom-economical route to incorporate and manipulate C=C bonds with far-reaching applications in industrial production, e.g., pharmaceuticals, cosmetics, fragrances, polymers, and fuels. 1b , 4 Various processes were developed with efficient catalysts based on transition metals: Ir, 5 Rh, 6 Pd, 7 Ru, 8 Cr, 9 Co, 10 Ni, 11 Fe, 12 and W, 13 among others ( Figure 1 a). Missing in this set of examples is the highly abundant and biocompatible manganese metal that remains unknown in olefin transposition so far.…”

A Dual CuH- and Pd-Catalyzed Stereoselective Synthesis of Highly Substituted 1,3-Dienes

“…Due to the utility of 1,3-dienes in organic synthesis, a variety of strategies to access these compounds have been developed. , Olefination of carbonyl compounds with stoichiometric allyl nucleophiles has been widely employed in the synthesis of conjugated dienes; − however, the products are generally obtained as inseparable E/Z mixtures (Figure A). , Although considerable advances have been made toward stereoselective olefination of carbonyl substrates, most methods to access 1,3-dienes result in the E,E- isomer. ,,, To avoid the formation of isomeric product mixtures, transition-metal-catalyzed cross-coupling utilizing preformed organometallic reagents and vinyl (pseudo)­halides has emerged as a practical route to stereoselectively synthesize dienes (Figure B). − In these processes, the geometry of the diene product is dictated by the stereochemistry of the coupling partners. Complementary approaches to prepare 1,3-dienes, including C–H activation of olefin starting materials, , rearrangements of allenes or alkynes, and ene-yne metathesis of acyclic precursors, , have also been developed. , …”

Cobalt-Catalyzed Z to E Geometrical Isomerization of 1,3-Dienes

“…In a combination of [CoBr 2 (dpppMe 2 )], zinc powder and ZnI 2 , Hilt and co-workers reported selective isomerization of terminal dienes, in which the diene double bonds migrated one position to afford 2 Z ,4 E -configured dienes as the products (Scheme b) . More recently, Mazet and Scaringi reported chemoselective conjugative isomerization of remote alkenes with a commercial available ruthenium-hydride catalyst ( Ru2 ), affording terminal-branched 1,3-dienes with moderate regioselectivity and high stereoselectivity (Scheme c) …”