Aryl Norbornanes and Analogues
via Palladium-Catalyzed Hydroarylation with Arenediazonium Tetrafluoroborates
Gabriele Bartoli, Sandro Cacchi*, Giancarlo Fabrizi, Antonella Goggiamani Dipartimento di Chimica e Tecnologie del
Farmaco, Università degli Studi ‘La
Sapienza’, P. le A. Moro 5, 00185 Rome,
Italy Fax: +39(06)49912780; e-Mail: sandro.cacchi@uniroma1.it;
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Publikationsverlauf
Received
18 June 2008 Publikationsdatum: 12. September 2008 (online)
The palladium-catalyzed hydroarylation of arenediazonium tetrafluoroborates
with norbornene derivatives and analogues in the presence of Pd(OAc)2 and i-Pr3SiH in THF affords hydroarylation
products containing the added aryl unit in the exo position
in good to high yields. The reaction tolerates a variety of useful
functional groups and can be performed as a one-pot procedure generating
the arenediazonium salt in situ.
1 For an excellent recent review on
the palladium-chemistry of arenediazonium salts, see: Roglans A.
Pla-Quintana A.
Moreno-Mañas M.
Chem. Rev.
2006,
106:
4622
2eNelson ML.
Ismail MY.
McIntyre L.
Bhatia B.
Viski P.
Hawkins P.
Rennie G.
Andorsky D.
Messersmith D.
Stapleton K.
Dumornay J.
Sheahan P.
Verma AK.
Warchol T.
Levy SB.
J.
Org. Chem.
2003,
68:
5838
When 1a was
subjected to the reaction conditions reported in Table
[¹]
(entry 5) omitting Pd(OAc)2 no
reduction product 4 was formed suggesting
that the reduction of 1a to 4 proceeds through
a palladium-catalyzed process.
Palladium-Catalyzed
Hydroarylation of 1a with 2a Generated In Situ A solution
of BF3˙OEt2 (140 µL, 1.1
mmol) in anhyd THF (1 mL) was cooled at -15 ˚C
and p-aminoacetophenone (135.1 mg, 1
mmol) was added. Then, tert-butyl nitrite
(160 µL, 1.3 mmol) in 1 mL of the same solvent was added
dropwise to the rapidly stirred reaction solution over a period
of 10 min. Following complete addition, the temperature of the solution was
maintained at -15 ˚C for 10 min and subsequently allowed
to warm to 5 ˚C in an ice-water bath over a period of
20 min. Then, the reaction mixture was warmed to r.t. and stirred
at the same temperature till the starting p-amino-acetophenone
was converted into p-acetylbenzenediazo-nium
tetrafluoroborate. The reaction mixture was cooled in an ice bath
and 1a (105.1 mg, 0.50 mmol), Pd(OAc)2 (5.6 mg,
0.025 mmol), i-Pr3SiH (205 µL,
1.0 mmol), and of anhyd THF (2 mL) were added. The reaction mixture
was allowed to warm to 20 ˚C and stirred at that
temperature for 6 h under argon (the reactor was protected from
light with aluminum film). After this time, the mixture was diluted with
EtOAc, washed with H2O, dried over Na2SO4,
and concentrated under reduced pressure. The residue was purified
by chromatography on silica gel [n-hexane-EtOAc, 90:10
(v/v)] to afford 106.3 mg (64% yield)
of 3a.
