Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes

Abstract

Excellent selectivity with complexes of DIOP, BDPP and Josiphos with E-1,3-dienes reacting faster than the Z-isomers at low temperatures.

Recent Advances in Enantioselective C–C Bond Formation via Organocobalt Species

“…6 In 2015, RajanBabu reported full details of the development of (asymmetric) 1,4-hydrovinylation of linear 1,3dienes, including the effect of promoters, the screening of achiral and chiral ligands, and the scope of both the racemic and enantioselective reactions. 7 For the enantioselective reaction, the broadest scope was achieved using (DIOP)CoCl 2 as the precatalyst and Me 3 Al or methylaluminoxane (MAO) as the activator, converting various alkyl-substituted 1,3dienes 1 into the chiral 1,4-hydrovinylation products 2 with Z-configuration (Scheme 1a). Other diphosphine ligands such as BDPP could also be used.…”

Tandem catalysis for asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

“…Early investigations with prototypical enynes 1a and 1b revealed that the ligands (Fig. 3 D ) we had successfully used in several other cobalt-catalyzed reactions,( 35 ) while giving high yields and excellent E : Z ratios of the products, gave unacceptable enantioselectivities (Table S3, entries 1-14). These included bis -diphenylphosphino-ligands ( S,S )-BDPP ( L1 ), ( S,S )-DIOP ( L2 ) and JOSIPHOS ( L3a and L3b ), BINAP and the bis -phospholane ligand L4 (Fig.…”

“…3 D ). After an extensive search,( 35 ) we identified CoCl 2 -complexes of phosphinooxazoline ligands (e.g., L8-L9 )( 36 ) as the most suitable catalysts for this tandem sequence(Tables S3 and S4). Among the activators Et 2 AlCl was found to be the most general (Table S4), often giving significantly better enantioselectivities than TMA which was used in initial screening studies.…”

“…Several other activators including Zn/ZnX 2 (X = Br, I)with complexes of various cobalt halides showed poor catalytic activity. ( 35 ) To establish the absolute configuration of the product, an authentic sample of ( R )- 4b was synthesized from the known ketone ( R )- 5 (Fig. 3 B ) ( 25, 37 ) Comparison of chiroptical properties and chromatographic behavior on chiral stationary phase GC established the product from the enyne 1b as ( S )- 4b .…”

“…The extreme sensitivity of this exacting tandem sequence towards the choice of ligand is apparent from the documented results (Table S3) ( 35 ). It is notably exemplified by the bis-phospholane L4 and the phosphinooxazoline ligand L10 (Fig.…”