Edging In with Iron

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Science  04 Sep 2009:
Vol. 325, Issue 5945, pp. 1183
DOI: 10.1126/science.325_1183d

Hydroboration is widely used in organic chemistry to append a borane and a hydrogen atom to respective carbons at either end of a double bond; the borane group can then be efficiently replaced to form a range of compounds such as alcohols. Wu et al. now show that an iron catalyst facilitates a variation on this reaction in 1,3-dienes: hydrocarbon derivatives with two double bonds separated by a single bond (C=C–C=C). Instead of adding boron and hydrogen to adjacent carbons, the reaction proceeds to add them at opposite edges of the four-carbon sequence, concomitantly creating a double bond between the central carbons. The catalyst forms in situ through reduction of an iminopyridine iron(II) complex by magnesium. In substrates substituted at one of the central carbons in the diene framework, the reaction is highly selective for the E product geometry about the newly formed double bond, complementing a previously developed palladium-catalyzed variant of this reaction class that favors the opposite stereochemistry. Varying the imine substituent on the ligand also allows the authors to modulate which end carbon receives the boron.

J. Am. Chem. Soc. 131, 10.1021/ja9048493 (2009).

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