Synthesis of Substituted 1,2-Dihydropyridines from Propargyl Vinyl Ethers and Allenic Vinyl Ethers
mosphere. After being stirred for 1 h, the mixture was
quenched with 10% aqueous potassium sodium tartrate
(5 mL). The mixture was allowed to come to room tempera-
ture. After 3 h, the mixture was filtered, and the solution
was extracted with CH2Cl2. After that, the organic layer was
washed with brine, and dried over anhydrous Na2SO4, fil-
tered and evaporated to give a residue.
The resulting crude material was used for the next step
without future purification. In a 25-mL round-bottomed
flask were placed the crude alcohol 9 and MeOH (5 mL),
KOH (140 mg, 5 mmol) was added. The mixture was re-
fluxed overnight and quenched by water. The mixture was
extracted with CH2Cl2. Combined extracts were washed with
brine and dried over Na2SO4. After removal of the solvent,
the residue was purified by flash column chromatography
on silica gel and give pyridine 10; yield: 63 mg (68%).
Scheme 7. Conversion of 1,2-dihydropyidines to pyridines.
Next, we investigated the conversion of 1,2-dihy-
dropyrodines to pyridines (Scheme 7). To simplify the
purification, we reduced ester 6-1a to acohol 9. The
tosyl group was removed by treatment with KOH in
MeOH to give pyridine 10 in 68% yield.
In summary, we have reported our preliminary re-
sults on gold-catalyzed tandem reactions for the syn-
thesis of substituted 1,2-dihydropyridines from prop-
argyl vinyl ethers or allenic vinyl ethers and primary
amines via gold-catalyzed [3,3]-sigmatropic rearrange-
ment/isomerization/amine condensation/6p-aza-elec-
trocyclization. 2,4-Dienals are the key intermediates
in these two tandem reactions. This discovery is signif-
icant not only as a novel tandem reaction sequence
but also as a mild, selective and efficient approach to
synthesize 1,2-dihydropyridines.
Acknowledgements
We are grateful for the National Basic Research Program of
China (No. 2010CB833200), the NSFC (20772051,
20972058), the “111” program from MOE of P. R. China.
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Experimental Section
Synthesis of 1,2-Dihydropyridines 6-1
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Synthesis of 1,2-Dihydropyridines 6-2
To a solution of the allenic vinyl ethers 2 (0.4 mmol) and
TsNH2 (136 mg, 0.8 mmol) in CH2Cl2 (3 mL) was added
(Ph3P)AuCl (8 mg, 0.02 mmol) and AgBF4 (6 mg,
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silica gel.
Synthesis of Pyridines 10
To
a
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Adv. Synth. Catal. 2010, 352, 2450 – 2454
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2453