Chemistry

More Than a Solvent

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Science  17 Dec 2004:
Vol. 306, Issue 5704, pp. 2003
DOI: 10.1126/science.306.5704.2003c

Replacement of a carbonyl oxygen with a methylene (CH2) group is often necessary in organic synthesis, but the typical methods for doing so involve sensitive reagents, such as highly basic ylides (Wittig reaction) or titanocene derivatives (Tebbe's and Grubbs' reagents). In a pair of papers, Yan et al. describe a convenient alternative system, based on a hetero-genous mixture of TiCl4, Mg powder, and tetrahydrofuran, which uses the common solvent dichloromethane as the source of CH2. The readily available reagents are simply mixed with aldehyde or ketone substrate, and the reaction proceeds within an hour. The nonbasic conditions tolerate a wide range of substrates, without disturbing acidic hydrogens or olefins prone to isomerization. Moreover, the reaction can proceed under severe steric constraints that block the titanocene systems. The second paper shows that increasing the Mg-to-TiCl4 ratio broadens the scope to include esters. — JSY

Org. Lett. 10.1021/ol0478887; 10.1021/ol047887e (2004).

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