Chemistry

Small, Yet Effective

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Science  25 Jan 2002:
Vol. 295, Issue 5555, pp. 589
DOI: 10.1126/science.295.5555.589b

Organic syntheses often require an intricate and ingenious choreography of reactions—to add needed fragments, to subtract excess pieces, and to protect and deprotect otherwise vulnerable parts of the molecule. In this last category, blocking groups usually exert their effects directly through masking; for instance, in the use of t-butyloxycarbonyl to cover up the NH2-terminal amino functionality during peptide synthesis. Vedejs and Little describe how a small blocking group, deuterium, helps to direct an anionic cyclization toward the desired product. The critical difference appears to be a large kinetic isotope effect; indole C-H lithiation is favored over tin-lithium exchange by about 10 to 1, but tin-lithium exchange is favored by about 4 to 1 over indole C-D lithiation. — GJC

J. Am. Chem. Soc.

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