A cascade of products
UK researchers have developed a cascade reaction strategy, to prepare heterocylic building blocks, using N-heterocyclic carbenes as catalysts.
The ability to combine many separate chemical steps into a single cascade protocol, to produce organic building blocks from simple organic starting materials, is highly desirable. N-heterocyclic carbenes (NHCs) are commonly used in organometallic processes, but have more recently been employed as organocatalysts and can promote very diverse series of reactions.
Andrew Smith and colleagues at the University of St Andrews, along with AnnMarie O'Donoghue and colleagues at the University of Durham, have demonstrated that sub-stoichiometric quantities of NHCs (5 mol%) can promote the formation of carboxyazlactones from azlactones in a two-step tandem reaction process. They have also been able to show that this protocol can be extended to multi-step reaction sequences.
The motivation behind this work was to develop 'nucleophilic catalysts that show wide functional group tolerance and are capable of promoting a range of selective and efficient chemical transformations,' said Smith.
Smith believes the next challenge is to introduce asymmetry into these sorts of cascade reactions which would allow the efficient production of enantiomerically pure products.
Original publication: Andrew Smith et al., Chem. Commun., 2008
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