Communications
NH2), 3.58–3.62 (m, 2H), 3.37 (br s, 2H, NH2), 2.73 (sept, J = 6.6 Hz,
2H, CH(CH3)2), 2.44 (s, 2H, CH2), 2.11–1.83 (m, 12H), 1.43 (s, 6H,
CH3), 1.35 (d, J = 6.6 Hz, 6H, CH(CH3)2), 1.34 ppm (d, J = 6.6 Hz,
6H, CH(CH3)2); 13C NMR (75 MHz, CD2Cl2): d = 237.8 (Ccarbene),
147.8 (d, JC,F = 232.9 Hz, Cquat), 144.7 (o-C), 138.0 (d, JC,F = 236.3 Hz,
Cquat), 135.9 (d, JC,F = 253.6 Hz, Cquat), 135.2 (Cipso), 130.0 (p-CH),
124.9 (m-CH), 78.2 (Cquat), 63.8 (Cquat), 47.9 (CH2), 38.4 (CH2), 36.7
(CH), 35.4 (CH2), 33.9 (CH2), 28.8 (CH and CH3), 27.7 (CH), 26.5
(CH), 26.3 (CH3), 22.5 (CH3).
General hydroamination procedure: CDCl3 or C6D6 (0.4 mL), the
alkyne or allene (0.5 mmol), anhydrous hydrazine (0.064 g,
2.0 mmol), and the internal standard 1,4-di-tert-butylbenzene
(10 mg, 0.05 mmol) were added to either complex C (0.032 g,
0.025 mmol) or a mixture of the [(CAAC)AuCl] complex (0.015 g,
0.025 mmol) and KB(C6F5)4 (0.018 g, 0.025 mmol) in a dried J Young
NMR tube. For experiments with a low catalyst loading (0.1 mol%),
0.3 mg of the [(CAAC)AuCl] complex and 0.4 mg of KB(C6F5)4 were
used. The tube was sealed, placed in an oil bath behind a blast shield,
and heated at the temperature specified. The reaction was monitored
by NMR spectroscopy. Products 2a–i and 4j were purified by column
chromatography on florisil. Product 6b was purified by recrystalliza-
tion from CHCl3.
these cyclization processes to enyne 1j. The first step, a
Markovnikov hydroamination of the triple bond, took place
at 908C to yield the corresponding hydrazone 2j. Then, as
observed by Nakhai and Bergman,[20] 2j could be thermally
converted (1508C, 2 h) into the indazole derivative 3j.
Interestingly, further heating at 1508C for 24 h without an
oxidant induced the aromatization of 3j by dehydrogenation
and afforded 4,5,6,7-tetrahydro-3-methyl-1H-indazole (4j),
which was isolated in good yield (77%).
We also investigated the hydroamination of allenes with
hydrazine (Scheme 4). When 1,2-propadiene (5a) was treated
with H2NNH2, the formation of a 2:1 mixture of hydrazone 6a
Received: January 28, 2011
Published online: May 5, 2011
Keywords: alkynes · gold complexes · homogeneous catalysis ·
.
hydrazine · hydroamination
Scheme 4. Catalytic hydroamination of allenes with hydrazine. [a] The
yield was estimated by 1H NMR spectroscopy. [b] Yield of the isolated
product.
[1] a) D. OꢀHagan, Nat. Prod. Rep. 2000, 17, 435 – 446; b) A.
2862 – 2892; c) J. W. Daly, H. M. Garraffo, T. F. Spande in The
Alkaloids: Chemistry and Pharmacology, Vol. 43 (Ed.: G. A.
Cordell), Academic Press, San Diego, 1993, pp. 185 – 288; d) A.
The Alkaloids: Chemistry and Pharmacology, Vol. 43 (Ed.: G. A.
Cordell), Academic Press, San Diego, 1993, pp. 119 – 183.
[2] S. A. Lawrence, Amines: Synthesis, Properties, and Applications,
Cambridge University Press, New York, 2004.
[3] For reviews on hydroamination reactions, see: a) K. D. Hesp, M.
K. C. Hultzsch, M. Yus, F. Foubelo, M. Tada, Chem. Rev. 2008,
Synth. Org. Chem. Jpn. 2006, 64, 778 – 779; g) P. W. Roesky, Z.
3368 – 3398; m) M. Beller, A. Tillack, J. Seayad, Transition
Metals for Organic Synthesis, 2nd ed., Wiley-VCH, Weinheim,
2004, pp. 403 – 414.
and allylhydrazine (7a) was observed (98% conversion after
14 h at 1308C). The addition of hydrazine to 1,2-dienes is not
restricted to the parent allene 5a. Tetraphenyl-1,2-propadiene
(5b) underwent hydroamination to afford the hydrazone
derivative 6b in more than 90% yield after 4 h at 1508C; the
observed regioselectivity is probably due to steric factors.
The results outlined herein demonstrate that the strong s-
donor and p-acceptor properties of cyclic (alkyl)-
(amino)carbenes enable the preparation of very robust
gold–hydrazine complexes, which are nevertheless catalyti-
cally active. Since gold complexes display excellent func-
tional-group tolerance as well as low air and moisture
sensitivity, these reactions should be ideal initial steps for
the synthesis of acyclic and heterocyclic bulk chemicals. This
study conquers the difficulties associated with the use of
hydrazine and opens an avenue for extensive applications.
Experimental Section
All manipulations were performed under an atmosphere of dry argon
by using standard Schlenk techniques. Water- and oxygen-free
solvents were employed.
[6] a) N. N. Greenwood, A. Earnshaw, Chemistry of the Elements,
Elsevier, Oxford, 1998, pp. 427 – 431; b) “Hydrazine”: B. A.
Roden in Encyclopedia of Reagents for Organic Synthesis (Ed.:
Synthesis of complex C: The [(CAAC)AuCl] complex (0.305 g,
0.5 mmol), KB(C6F5)4 (0.359 g, 0.5 mmol), anhydrous hydrazine
(0.128 g, 4.0 mmol), and CHCl3 (12 mL) were placed in a Schlenk
tube. The mixture was stirred for 30 min at ambient temperature, and
then potassium chloride was filtered off. Removal of the solvent and
excess hydrazine under vacuum gave the gold complex C as a white
1
solid (94% yield). M.p.: 1208C; H NMR (300 MHz, C6D6): d = 7.49
(d, J = 7.7 Hz, 1H, CH), 7.32 (d, J = 7.7 Hz, 2H, CH), 4.72 (br s, 2H,
5562
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 5560 –5563