Science of Synthesis

Cherkinsky, M.; Levinger, S., Science of Synthesis, (2010) 47, 481.

General Introduction

The metal-mediated allylic substitution reaction of structurally diverse allylic electrophiles with carbon nucleophiles is an excellent method for forming new, branched alkenes. Generally, allylic alkylation can be catalyzed by many metal complexes, derived from palladium, copper, nickel, platinum, rhodium, iridium, iron, and molybdenum. The major advantage of copper-mediated reactions in contrast to other metals is that copper catalysts allow the use of hard nucleophiles including Grignard, organozinc, and organolithium reagents, and thus are complementary to palladium-catalyzed reactions. Moreover, copper-catalyzed allylic substitutions normally proceed with high SN2′ regioselectivity. A significant advantage of these processes is the high compatibility with many functional groups on both the substrate and the nucleophile. Also important is that copper salts are generally significantly less expensive than those of palladium. The topic has been covered in several reviews.[‌1‌–‌3‌] The usually high SN2′ regioselectivity of copper-catalyzed allylic alkylations may create stereogenic centers by the attack of a nonstabilized carbon nucleophile on an allylic substrate. Thus, copper-catalyzed SN′ reactions have been efficiently exploited for the synthesis of chiral alkenes using either chiral allylic substrates or catalysts with chiral ligands.[‌4‌–‌9‌]

References

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