The Second Step of the Halogen/Metal Exchange Reaction

Abstract

[reaction: see text] The conversion of the iodine ate-complex 5 to the Grignard reagent 6 follows a rate law first order in 5 and in magnesium ions. In addition to this normal pathway of the halogen-metal exchange process, the conversion of 5 to 6 is catalyzed by a number of diverse "electrophiles". This points to a SET-initiated radical chain process as a second pathway for the conversion of the iodine ate-complex 5 to the Grignard reagent 6.

The quest for chiral Grignard reagents

“…If, however, the diastereomeric ate-complexes 27a and 27b were rapidly to equilibrate, 25 dynamic kinetic resolution 26 of the ate-complexes 27 by the chiral cation in the second step, i.e. the formation of the a-iodoalkyl Grignard reagents 25a and 25b could be expected to be high, as now the magnesium cation with its chiral entourage directly attacks 27 at the new stereogenic centre (Scheme 12).…”

Enantiodivergence in the Reactions of a Highly Enantiomerically Enriched Silyllithium Compound with Benzyl Halides: Control of Inversion and Retention by Selection of Halide

“…Quantum‐chemical studies of Boche et al on methyl‐ate complexes suggest that ate complexes are pivotal intermediates in halogen–lithium exchange reactions with alkyllithium compounds 13e. Experimental and theoretical studies of Hoffmann et al as part of the synthesis of optically active alkylmagnesium compounds show that ate complexes are also involved in iodine–magnesium exchange reactions with alkylmagnesium compounds 13a–c…”

Enantiodivergenz bei Umsetzungen einer hoch enantiomerenangereicherten Silyllithium‐Verbindung mit Benzylhalogeniden: Steuerung von Inversion und Retention durch Wahl des Halogenids

“…Quantenchemische Studien von Boche et al über Methyl‐at‐Komplexe deuten darauf hin, dass at‐Komplexe bei Halogen‐Lithium‐Austausch‐Reaktionen mit Alkyllithium‐Verbindungen entscheidende Intermediate sind 13e. Experimentelle und theoretische Studien von Hoffmann et al im Rahmen der Synthese von optisch aktiven Alkylmagnesium‐Verbindungen zeigen, dass auch beim Iod‐Magnesium‐Austausch mit Alkylmagnesium‐Verbindungen at‐Komplexe beteiligt sind 13a–c…”