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

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.

boron - asymmetric catalysis - silicon - regioselectivity - alkenes

References

For enantioselective catalytic diboration, see:

1a Morgan JB. Miller SP. Morken JP. J. Am. Chem. Soc.  2003,  125:  8702 

For Rh-catalyzed diboration of alkenes, see:

1b Baker RT. Nguyen P. Marder TB. Westcott SA. Angew. Chem., Int. Ed. Engl.  1995,  34:  1336 

1c Dai C. Robins EG. Scott AJ. Clegg W. Yufit DS. Howard JAK. Marder TB. Chem. Commun.  1998,  1983 

1d Nguyen P. Coapes RB. Woodward AD. Taylor NJ. Burke JM. Howard JAK. Marder TB. J. Organomet. Chem.  2002,  652:  77 

For Pt-catalyzed diboration of alkenes, see:

1e Iverson CN. Smith MR. Organometallics  1997,  16:  2757 

1f Ishiyama T. Yamamoto M. Miyaura N. Chem. Commun.  1997,  689 

1g Marder TB. Norman NC. Rice CR. Tetrahedron Lett.  1998,  39:  155 

1h Ishiyama T. Momota S. Miyaura N. Synlett  1999,  1790 

2a Hydrogen peroxide and NaOH is most commonly used for oxidation of C-B bonds: Zweifel G. Brown HC. Org. React.  1963,  13:  1 

2b A number of other oxidants have also been employed for this purpose, see: Kabalka GW. Wadgaonkar PP. Shoup TM. Organometallics  1990,  9:  1316 ; and references cited therein

3 Miller SP. Morgan JB. Nepveux FJ. Morken JP. Org. Lett.  2004,  6:  131 

For examples of cross-coupling with secondary C-B bonds, see:

4a Kirchhoff JH. Dai C. Fu GC. Angew. Chem. Int. Ed.  2002,  41:  1945 

4b Kataoka N. Shelby Q. Stambuli JP. Hartwig JF. J. Org. Chem.  2002,  67:  5553 

5 Goddard J.-P. Le Gall T. Mioskowski C. Org. Lett.  2000,  2:  1455 

For lead references to other homologations, see:

6a Matteson DS. Majumdar D. J. Am. Chem. Soc.  1980,  102:  7590 

6b Matteson DS. Majumdar D. Organometallics  1983,  2:  1529 

6c Chen A. Ren L. Crudden CM. J. Org. Chem.  1999,  64:  9704 

6d Tsai DJS. Matteson DS. Organometallics  1983,  2:  236 

6e Sadhu KM. Matteson DS. Organometallics  1985,  4:  1687 

6f Hara S. Satoh Y. Suzuki A. Chem. Lett.  1982,  1289 

6g Leung T. Zweifel G. J. Am. Chem. Soc.  1974,  96:  5620 

6h Brown HC. Singh SM. Organometallics  1986,  5:  994 

6i For diastereoselective homologation of C-B bonds with prochiral homologation reagents, see: Hoffmann RW. Stiasny HC. Tetrahedron Lett.  1995,  36:  4595 

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.

9 Soderquist JA. Najafi MR. J. Org. Chem.  1986,  51:  1330