When gold can do what iodine cannot do: A critical comparison

Abstract

Gold catalysis has emerged as one of the most dynamic fields in organic synthesis. Only recently, more and more domino processes, for which gold pre-catalysts were found to be outstandingly effective, were paralleled by employing iodine electrophiles in place of gold compounds. This review highlights how, in certain cases, iodonium activation can match gold-catalyzed reactions to construct identical product scaffolds. Likewise, processes are discussed where mostly identical starting materials are transformed into diverse frameworks depending on whether gold or iodonium activation was used to trigger the reaction.

Keywords: catalysis; cycloisomerizations; domino reactions; gold; iodine.

Scheme 1

Mechanistic scenarios for alkyne activation.

Scheme 2

Synthesis of 3(2H)-furanones.

Scheme 3

Synthesis of furans.

Scheme 4

Formation of dihydrooxazoles.

Scheme 5

Variation on indole formation.

Scheme 6

Formation of naphthalenes.

Scheme 7

Formation of indenes.

Scheme 8

Iodocyclization of 3-silyloxy-1,5-enynes.

Scheme 9

5-Endo cyclizations with concomitant nucleophilic trapping.

Scheme 10

Reactivity of 3-BocO-1,5-enynes.

Scheme 11

Intramolecular nucleophilic trapping.

Scheme 12

Approach to azaanthraquinones.

Scheme 13

Carbocyclizations with enol derivatives.

Scheme 14

Gold-catalyzed cyclization modes for 1,5-enynes.

Scheme 15

Iodine-induced cyclization of 1,5-enynes.

Scheme 16

Diverse reactivity of 1,6-enynes.

Scheme 17

Iodocyclization of 1,6-enynes.

Scheme 18

Cyclopropanation of alkenes with 1,6-enynes.

Scheme 19

Cyclopropanation of alkenes with 1,6-enynes.