Arkady Krasovskiy

Selective Mono-and 1,2-Difunctionalisation of Cyclopentene Derivatives via Mg and Cu Intermediates

A single Br/Mg exchange of 1,2-dibromocyclopentene with iPrMgCl LiCl provides the corresponding beta-bromocyclopentenylmagnesium reagent, which can then be reacted with various electrophiles (yields: 65-82 %). In the presence of a secondary alkylmagnesium halide and Li2CuCl4 (2 mol %), these 2-bromoalkenylmagnesium compounds undergo bromine substitution and can then further react with electrophiles to give 1,2-difunctionalised cyclopentenes (63-79 %). The mechanism of this process is discussed.

Preparation of cyclic alkenylmagnesium reagents via an iodine/magnesium exchange

The reaction of various cyclic alkenyl iodides with i-PrMgCl.LiCl produces the corresponding alkenylmagnesium reagents under mild conditions. After reaction with various electrophiles, like allylic halides, disulfides, aldehydes and acid chlorides, the expected products are obtained in 53-91% yield. Remarkably, the mild conditions of the I/Mg-exchange tolerate the presence of sensitive diene functionalities.

9.03 – Magnesium

Organomagnesium reagents are used widely in all fields of organic synthesis. The development of organomagnesium chemistry for organic synthesis has been accelerated by the extensive use of transition metal catalysis and by the finding of new preparations of polyfunctional Grignard reagents, using the I/Mg- and Br/Mg exchange reactions. The Grignard reagents remain key reagents for the organic synthesis. The rapid growth of the chemistry of Grignard reagents during the last decade is mostly connected with the availability of new methods for their preparation, which are compatible with the presence of the functional groups. The recent developments in the field of organomagnesium chemistry have been reviewed in the last decade.