Nickel-catalyzed coupling reactions of alkyl electrophiles, including unactivated tertiary halides, to generate carbon-boron bonds.
Through the use of a catalyst formed in situ from NiBr(2)·diglyme and a pybox ligand (both of which are commercially available), we have achieved our first examples of coupling reactions of unactivated tertiary alkyl electrophiles, as well as our first success with nickel-catalyzed couplings that generate bonds other than C-C bonds. Specifically, we have determined that this catalyst accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates, a family of compounds with substantial (and expanding) utility, under mild conditions; indeed, the umpolung borylation of a tertiary alkyl bromide can be achieved at a temperature as low as -10 °C. The method exhibits good functional-group compatibility and is regiospecific, both of which can be issues with traditional approaches to the synthesis of alkylboronates. In contrast to seemingly related nickel-catalyzed C-C bond-forming processes, tertiary halides are more reactive than secondary or primary halides in this nickel-catalyzed C-B bond-forming reaction; this divergence is particularly noteworthy in view of the likelihood that both transformations follow an inner-sphere electron-transfer pathway for oxidative addition.
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Alexander S
AS
Dudnik
Gregory C
GC
Fu
D001895:Boron / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D004563:Electrochemistry; D006219:Halogens / Q000737:chemistry*; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*
D006219:Halogens; D009930:Organic Chemicals; D002244:Carbon; D009532:Nickel; D001895:Boron