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Synlett 2005(11): 1749-1751  
DOI: 10.1055/s-2005-869873
LETTER
© Georg Thieme Verlag Stuttgart · New York

Regioselective Homologation of Bis(boronate) Intermediates Derived from Rhodium-Catalyzed Diboration of Simple Alkenes

Diane M. Kalendra, Rebecca A. Dueñes, James P. Morken*
Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
Fax: +1(919)9628229; e-Mail: morken@unc.edu;
Further Information

Publication History

Received 30 March 2005
Publication Date:
09 June 2005 (online)

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Abstract

Regioselective homologation of alkyl-1,2-bis(catecholboronates) may be accomplished by treatment of these reactive intermediates with TMSCHN2. A convenient process is reported where alkene diboration and the subsequent homologation reaction are accomplished in the same reaction flask.

Key words

boron - asymmetric catalysis - silicon - regioselectivity - alkenes

7

Representative Procedure.
A dry 16 mL vial was charged with 3.7 mg (0.013 mmol) of {bicyclo[2.2.1]hepta-2,5-diene}-(2,4-pentanedionato)-rhodium(I), 5.5 mg (0.013 mmol) of (S)-QUINAP, and 1.0 mL of toluene in a dry-box. The resultant solution was stirred for 3 min before 89 mg (0.37 mmol) of bis(catecholato)diboron was added. After 3 more minutes, 32 µL (0.25 mmol) of 3,3-dimethyl-1-butene was added and the solution allowed to stir for 24 h at ambient temperature. The vial was then wrapped in foil and 0.50 mL (1.0 mmol) of trimethylsilyldiazomethane (2.0 M in hexanes) was added. After stirring for 8 h at 80 °C an additional 0.50 mL (1.0 mmol) of trimethylsilyldiazomethane (2.0 M in hexanes) was added. After stirring an additional 8 h at 80 °C, the solution was cooled to 0 °C and NaOH (1.0 mL of 3 M) and H2O2 (1 mL of 30% solution) were added cautiously. After 6 h, the mixture was treated with 2 mL of sat. aq Na2S2O3 and extracted with EtOAc. The crude material was purified by silica gel chromatography (3:1 hexanes-EtOAc) to provide 25 mg (49% yield) of pure 4,4-dimethyl-1-(trimethylsilyl)pentane-1,3-diol.

8

Procedure for Protodesilylation.
To 38 mg of 4,4-dimethyl-1-(trimethylsilyl)pentane-1,3-diol (0.19 mmol, obtained from entry 2, Table [1] ) was added 2.4 mL of THF followed by 0.38 mL of TBAF (1.0 M in THF, 0.38 mmol). After stirring at 70 °C for 23 h the mixture was evaporated to dryness and the residue resuspended in EtOAc. After washing with H2O, the solution was concentrated and the crude material purified on silica gel (2:1 hexanes-EtOAc) to give 9.4 mg (38% yield) of 4,4-dimethyl-1,3-pentanediol.