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. 2009 Dec 30;131(51):18234-5.
doi: 10.1021/ja9089928.

Vicinal diboronates in high enantiomeric purity through tandem site-selective NHC-Cu-catalyzed boron-copper additions to terminal alkynes

Yunmi Lee  1 , Hwanjong Jang, Amir H Hoveyda
Affiliations

Vicinal diboronates in high enantiomeric purity through tandem site-selective NHC-Cu-catalyzed boron-copper additions to terminal alkynes

Yunmi Lee et al. J Am Chem Soc. .

Abstract

A Cu-catalyzed protocol for conversion of terminal alkynes to enantiomerically enriched diboronates is reported. In a single vessel, a site-selective hydroboration of an alkyne leads to the corresponding terminal vinylboronate, which undergoes a second site-selective and enantioselective hydroboration. Reactions proceed in the presence of 2 equiv of commercially available bis(pinacolato)diboron [B(2)(pin)(2)] and 5-7.5 mol % loading of a chiral bidentate imidazolinium salt, affording diboronates in 60-93% yield and up to 97.5:2.5 enantiomeric ratio (er). The enantiomerically enriched products can be functionalized to afford an assortment of versatile organic molecules. Enynes are converted to unsaturated diboronates with high chemo- (>98% reaction of alkyne; <2% at alkene) and enantioselectivity (e.g., 94.5:5.5 er).

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Figures

Scheme 1
Scheme 1. Initial Investigations
Scheme 2
Scheme 2. Influence of NHC Structure on Site Selectivity and Enantioselectivity of Boron–Copper Additionsa
a Conversions for reactions with 0.9 equiv 1 are based on the amount of this reagent and determined by 1H NMR analysis. Mes = (2,4,6)-trimethylphenyl.
See this image and copyright information in PMC

References

    1. Lee Y, Hoveyda AH. J. Am. Chem. Soc. 2009;131:3160–3161. - PMC - PubMed
    1. Dang L, Lin Z, Marder TB. Organometallics. 2008;27:4443–4454. and references cited therein.

    1. For selected reviews regarding catalytic diboron additions to alkenes (including enantioselective variants), see: Beletskaya I, Moberg C. Chem. Rev. 2006;106:2320–2354.. Burks HE, Morken JP. Chem. Commun. 2007:4717–4725.. Dang L, Lin Z, Marder TB. Chem. Commun. 2009:3987–3995.. See the SI for additional reviews.

    1. For Rh-catalyzed enantioselective hydroborations (up to 89.5:10.5 er) of a vinylboronate [(E)-2-(phenylethenyl)-1,3,2-dioxaborolane], see: Wiesauer C, Weissensteiner W. Tetrahedron: Asymm. 1996;7:5–8.

    1. For Pt- and Pd-catalyzed double-hydrosilylation of arylacetylenes, see: Shimada T, Mukaide K, Shinohara A, Han JW, Hayashi T. J. Am. Chem. Soc. 2002;124:1584–1585.

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