We have reported on novel cobalt catalysts for co-dimerization of ethylene and various cyclic and acyclic 1,3-dienes (Scheme 1). This hydrovinylation reaction (HV), provides an expedient entry into nearly enantiopure 1,4-skipped dienes(2), with excellent yields (&gt;95%) and enantioselectivities (92% to 98% major isomer) A major limitation of this reaction is the lack of reactivity with functionalized alkenes. While investigating the expansion of the scope of the reaction we discovered a more general protocol where we can use other alkenes such as acrylates (in addition to ethylene) to afford highly valuable homodimerization products (5a~5c, Scheme 2). We discovered that Co(I) catalysts of the type (P~P)CoX or (P~N)CoX (4, X= Br, Cl, and alkenyl) with appropriate Lewis acids effect this reaction, which appears to have broad scope. Thus a prototypical (E)-1,3-diene, 1 (1.0 eq), when treated with DPPPCoCl (0.05 eq), NaBARF(0.07 eq) and methyl acrylate (1.1 eq) in methylene chloride(1 mL) affords a mixture of coupling products 5a-c (5a:5c:5b; 7.7:1:1) in 92 % isolated yield. An enantioselective version of this reaction has been developed in which 5a can be produced in 91% isolated yield and 97% ee. Further progress in this area will be discussed.

Enantioselective heterodimerization of 1,3-dienes and acrylates

253rd National Meeting (2017)

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