Allenes have proven to be versatile substrates for metal catalyzed diboration reactions.1,2 Although symmetrical diboron reagents such as B2(pin)2 (pin = pinacolate) and B2(cat)2 (cat = catecholate) are widely used in these reactions, there are limited examples of diboration with unsymmetrical diboron reagents.3 In this work, an unsymmetrical diboron reagent, (pin)B-B(dan) (1  , dan = naphthalene-1,8-diaminate) was reacted with a series of 1,1-disubstituted allenes chemo- and regioselectively.  A catalyst and ligand screening found the combination of Pt(dba)3 (dba = dibenzylideneacetone) and Sphos (2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl) provided the best selectivity with good yields (74-98%). This optimized reaction condition tolerates both electron withdrawing and donating groups on the 1,1-diaryl allene substrates. Steric control ensures that both boryl moieties add to the terminal double bond. Moreover, the pinacol boronate preferentially attaches to the sp2 hybridized carbon. The structures of the major isomers were confirmed by X-ray crystallography and 2D 1H NMR. We further demonstrate the application of these intermediates in the chemoselective Suzuki cross-coupling reaction of the pinacol protected over the 1,8-diaminonaphathelene protected boronate moiety to afford a trisubstituted alkene.(1) Ishiyama, T.; Kitano, T.; Miyaura, N. Tetrahedron Lett. 1998  , 39, 2357.(2) Pelz, N. F.; Woodward, A. R.; Burks, H. E.; Sieber, J. D.; Morken, J. P. J. Am. Chem. Soc. 2004  , 126, 16328.(3) Iwadate, N.; Suginome, M. J. Am. Chem. Soc. 2010  , 132, 2548.

Chemo� and regioselective diboration of allenes with differentially protected diboron

247th National Meeting (2014)

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