Chemistry Reference
In-Depth Information
An important advantage of the nickel-catalyzed transformations is the use of aldehydes as
carbon monoxide surrogates, in which case the only limitation of the reaction is the nature
of the reactant itself: the need to use 4-pentynal or 5-hexynal reduces the applicability of this
methodology. Another interesting alternative is the use of Au catalysis for the isomerization
of alkynes and intramolecular cyclization. Gold catalysis is, nowadays, one of the most
exciting fields in organic catalysis and new developments are expected. However, it is clear
that circumventing the use of highly toxic carbon monoxide is the alternative of choice and
recent developments in this area are very promising.
Experimental
Typical experimental Procedure for the nickel catalyzed carbonylative cycloaddition
of allyl halides and acetylenes reported by Moret
´
oetal.
38
A solution of nickel(0) tetracarbonyl (40mmols) in dry acetone (5mL) was added dropwise
at 15
◦
C into a solution of the alkyne (20mmols) and allyl chloride (40mmols) in acetone-
methanol (40:5mL) placed in a thermostated raction flask, equipped with magnetic stirrer,
dropping funnel, thermometer, gas inlet, and mercury valve, which had been previously
purged with Argon, and the reaction mixture was kept for 15 h at 14
◦
C. Then, the temper-
ature was raised to 40
◦
C and after one additional hour a stream of nitrogen was passed
through the mixture for 5 h, keeping the temperature at 40
◦
C, to remove any unreacted
nickel(0) tetracarbonyl and most of the solvent. The remaining solvent was removed under
vacuum and the crude reaction product was treated with water (40mL) and repeatedly
extracted with dichloromethane. The extract was dried over magnesium sulfate and after
removal of the solvent, flash chromatography of the residue afforded the cyclopentenone.
Typical experimental procedure for the reaction of Fischer carbene complexes with
alkynes reported by Moser.
22
A solution of carbene complex (2.0mmols) and TIPS-substituted phenyl acetylene
(2.40mmols) in benzene (20mL) was degassed using several freeze-pump-thaw cycles.
The solution was then heated at reflux for 12 h. Upon cooling to room temperature,
the solvents were removed under reduced pressure and the residue purified via flash
chromatography.
Typical experimental procedure for the rearrangenment of 1,1-diethynilcarbinol-
acetates reported by Oh.
80
In a small flask, 3mol% of AuCl(PPh
3
) and SbF
6
was taken in 1.0mL of wet
dichloromethane at 0
◦
C. It was then allowed to reach room temperature (25
◦
C) fol-
lowed by addition of 1,1-diethylcarbinolacetate dissolved in the minimum volume of wet
dichloromethane. The resulting mixture was stirred for 1-2 h at room temperature and mon-
itored periodically by TLC. Upon completion, the solvent was subjected to flash column
chromatography to afford the pure cyclopentenones.
References and Notes
[1] For an excellent and inspirational review about transition metal catalyzed synthesis
of cyclopentenones see: S. E. Gibson, S. E. Lewis, N. Mainolfi, “Transition metal-
mediated routes to cyclopentenones”
J. Org. Chem.
,
689
, 3873-3890, (2004).
