Catalytic Enantioselective Hetero-dimerization of Acrylates and 1,3-Dienes

Abstract

1,3-Dienes are ubiquitous and easily synthesized starting materials for organic synthesis and alkyl acrylates are among the most abundant and cheap feedstock carbon sources. A practical, highly enantioselective union of these two readily available precursors giving valuable, enantio-pure skipped 1,4-diene esters (with two configurationally defined double bonds) is reported. The process uses commercially available cobalt salts and chiral ligands. As illustrated by the use of 20 different substrates including 17 prochiral 1,3-dienes and 3 different acrylates, this heterodimerization reaction is tolerant of a number of common organic functional groups (e.g., aromatic substituents, halides, isolated mono- and di-substituted double bonds, esters, silyl ethers and silyl enol ethers). The novel results including ligand, counter ion and solvent effects uncovered during the course of these investigations show a unique role of a possible cationic Co(I) intermediate in these reactions. The rational evolution of a mechanism-based strategy that led to the eventual successful outcome and the attendant support studies may have further implications for the expanding use of low-valent group 9 metal complexes in organic synthesis.

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

“…The ligand, counterion and solvent effects documented here and in the literature for cobalt-catalyzed olefin dimerization reactions point to a Co(I)/Co(III)-catalytic cycle, not much different from what we proposed recently for the dimerization of 1,3-dienes and methyl acrylate ( 38 ). As in the case of that heterodimerization, the tandem sequence disclosed here does not proceed with isolated Co(I) complexes.…”

“…Specifically, we have attempted to carry out the reaction of 1a with ethylene (Fig. 3 A ) under catalysis by isolated cobalt(I) sources [ L8a ]CoCl and [ L8a ]CoEt ( 38 ) in the absence of any activators and found no reaction except for decomposition of the starting materials on prolonged time. However, addition of a Lewis acid, B(C 6 F 5 ) 3 , resulted in modest yields (up to 50%) of the cyclobutene product 3a .…”

Synergistic Catalysis for Stereodivergent Synthesis of trans- and cis-Skipped Dienes

“…9 More recently, an efficient regio-and enantioselective hydroalkenylation reaction of 1,3-diene with acrylate was recently developed by RajanBabu group with a combination of commercially available cobalt salt as the catalyst, chiral ligand, and tetrakis-3,5-bis(trifluoromethylphenyl)borate (Na-BARF) as the activator, affording a series of enantioenriched skipped 1,4-diene esters with excellent enantioselectivity. 10 Transition-metal-mediated hydroallylation of alkynes also allows the convenient and stereodefined construction of skipped dienes from alkynes (Scheme 3). One notable example of this approach is that titanium-mediated reductive cross-coupling of simple allylic alcohols and alkynes, developed by the Micalizio group, giving the functionalized 1,4dienes with a high degree of stereoselective control.…”

Cobalt‐Catalyzed Diastereo‐ and Enantioselective Hydroalkenylation of Cyclopropenes with Alkenylboronic Acids

“…[8b] In the field of catalytic enantioselective functionalization of cyclopropenes,R h-catalyzed hydrostannation, [9] hydroboration, [10] hydroformylation, [11] hydroacylation, [12] and Cucatalyzed hydroboration, [13] hydronitronylation, [14] carbocupration, [15] carbozincation, [16] carbomagnesiation, [17] hydroallylation, [18] and Fe- [19] and Pd-catalyzed carbozincation, [20] and lanthanide-catalyzed hydroamination, [21] hydroalkynylation, [22] addition of 2-methyl azaarenes, [23] and NHC-catalyzed hydroacylation [24] have been disclosed for enantioselective preparation of various functionalized cyclopropanes (Scheme 1b). [25] Theonly pioneering work is the Cu-catalyzed protocol with alkenylaluminum reagents as nucleophiles,a lbeit in moderate efficiency and enantiose- lectivity,and with limited scope. [25] Theonly pioneering work is the Cu-catalyzed protocol with alkenylaluminum reagents as nucleophiles,a lbeit in moderate efficiency and enantiose- lectivity,and with limited scope.…”

“…However,i ntroduction of diversified alkenyl groups onto ac yclopropyl ring has been rarely reported despite all the strategies mentioned above. [25] Theonly pioneering work is the Cu-catalyzed protocol with alkenylaluminum reagents as nucleophiles,a lbeit in moderate efficiency and enantiose- lectivity,and with limited scope. [26] Although enantioselective hydroboration of cyclopropenes followed by Pd-catalyzed cross-coupling with alkenyl halides constitutes an indirect approach to incorporate an alkenyl unit onto cyclopropyl rings, [9,13,27] we are interested in the development of am ore general and step-economical solution to this problem in combination with unprecedented Co catalysis.T he utility of more robust organoboronic acids,w ith higher functionalgroup tolerance and diversity,a sn ucleophiles in catalytic enantioselective functionalization of cyclopropenes provides ap romising solution.…”