title: Stereoconvergent synthesis of chiral allylboronates from an E/Z mixture of allylic aryl ethers using a 6-NHC-Cu(I) catalyst.
abstract: We present a 6-NHC-Cu(I) complex that provides α-substituted allylboronates using allylic aryl ether substrates. The method was discovered by comparison of the chemoselectivities exhibited by complexes 1a, 1b, 2, and 3. We observed that 1a preferentially reacts with electron-rich alkenes over electron-deficient alkenes. Development of an asymmetric method revealed that 1b reacts with both the E and Z isomers to provide the same absolute configuration without showing E-Z isomerization. This stereoconvergent reaction occurs with high yields (av 86%), high S(N)2' selectivity (>99:1), and high ee (av 94%) and exhibits wide functional-group tolerance using pure E or Z isomer or E/Z alkene mixtures. The stereoconvergent feature enables the use of many different olefination strategies for substrate production, including cross-metathesis. Chiral allylboronates could be purified by silica gel chromatography and stored in the freezer without decomposition.
authors.affiliation: Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
authors.forename: Jin Kyoon
authors.initials: JK
authors.lastname: Park
authors.forename: Hershel H
authors.initials: HH
authors.lastname: Lackey
authors.forename: Brian A
authors.initials: BA
authors.lastname: Ondrusek
authors.forename: D Tyler
authors.initials: DT
authors.lastname: McQuade
mesh_terms: D000498:Allyl Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D001897:Boronic Acids / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D003300:Copper / Q000737:chemistry; D004987:Ethers / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000498:Allyl Compounds; D001897:Boronic Acids; D004987:Ethers; D006571:Heterocyclic Compounds; D009942:Organometallic Compounds; C030011:carbene; D003300:Copper; D008697:Methane