CHEMISTRY: Double Duty

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Science  01 Apr 2005:
Vol. 308, Issue 5718, pp. 19d
DOI: 10.1126/science.308.5718.19d

Strategies for homogeneous catalysis of bimolecular reactions tend to focus on activating only one of the two reactants. Recently, several bimetallic systems have been developed for dual activation, but the interactions between the two different catalytic sites are often difficult to predict and control. Takita et al. show that a single trivalent indium catalyst can activate both nucleophile and electrophile in the same reaction mixture under relatively mild conditions. The reaction involves the addition of terminal alkynes to aldehydes or to ketones, and it generally requires deprotonation of the alkyne with stoichiometric organometallic base. The catalytic In(III) salt assumes this role in the presence of an amine base, and, at the same time, it acts as a Lewis acid to activate the carbonyl electrophile. Evidence for this dual function comes from infrared and nuclear magnetic resonance spectroscopy. The reaction proceeds under solvent-free conditions and produces high yields from aromatic aldehydes, which have resisted alternative approaches. InBr3 works best for aldehydes, whereas ketones require the triflate salt In(SO3CF3)3. — JSY

Org. Lett. 10.1021/ol050069h (2005).

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