Synlett 2015; 26(11): 1578-1580
DOI: 10.1055/s-0034-1380686
letter
© Georg Thieme Verlag Stuttgart · New York

1,3,5,7-Tetra(Bpin)azulene by Exhaustive Direct Borylation of Azulene and 5,7-Di(Bpin)azulene by Selective Subsequent Deborylation

Hidetaka Nishimura
a   Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
,
Maria N. Eliseeva
b   Merkert Chemistry Center, Department of Chemistry, Boston College, Chestnut Hill, MA 02467-3860, USA   Email: lawrence.scott@bc.edu
,
Atsushi Wakamiya
a   Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
,
Lawrence T. Scott*
b   Merkert Chemistry Center, Department of Chemistry, Boston College, Chestnut Hill, MA 02467-3860, USA   Email: lawrence.scott@bc.edu
› Author Affiliations
Further Information

Publication History

Received: 12 February 2015

Accepted after revision: 09 April 2015

Publication Date:
30 April 2015 (online)


We dedicate this letter to Professor K. P. C. Vollhardt for his inspirational leadership as a scientist, educator, and editor of Synlett

Abstract

Exhaustive borylation of azulene with excess bis(pinacolato)-diboron (B2pin2) under conditions that promote equilibration of the borylated azulenes provides a convenient one-step synthesis of 1,3,5,7-tetra(Bpin)azulene as the major product. The Bpin substituents at positions 1 and 3 can be conveniently removed from 1,3,5,7-tetra-(Bpin)azulene by treatment with trifluoroacetic acid at room temperature to give 5,7-di(Bpin)azulene. The utility of 5,7-di(Bpin)azulene as a synthetic precursor to 5,7-disubstituted azulenes that are otherwise difficult to access is demonstrated by Suzuki coupling to give the previously unknown 5,7-diphenylazulene.

Supporting Information

 
  • References and Notes

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  • 15 B2Pin2 (16.8 g, 66.0 mmol), [IrOMe(cod)]2 (1.99 g, 3.01 mmol), 4,4′-dimethyl-2,2′-bipyridyl (1.11 g, 6.01 mmol), and t-BuOK (168 mg, 1.50 mmol) were charged in the Schlenk flask and flushed with Ar. THF (13 mL) was added, and the mixture was heated at 50 °C for 10 min. Azulene (1.93 g, 15.0 mmol) was added, and the solution was stirred at 85 °C for 6 d. The mixture was cooled to r.t. and diluted with CH2Cl2 (100 mL). The solution was quenched with H2O (100 mL). The aqueous layer was extracted with CH2Cl2 (3 × 50 mL), and the combined organic layer was washed with H2O and brine, successively. The organic layer was dried over Na2SO4, filtered off, and concentrated under reduced pressure. The obtained crude product was washed with MeOH (200 mL) by sonication for 30 min, until purple solids formed. The solids were filtered and further washed with MeOH (100 mL) to give 3.62 g (5.73 mmol) of 2 in 38% yield as purple solids. See Supporting Information for characterization data.
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