Cyclomagnesation of cycloalkynes with the use of RMgR’ catalyzed by zirconium complexes

Abstract

The intermolecular cyclomagnesation of cycloalkynes and joint cyclomagnesation of cycloalkynes and disubstituted acetylenes was carried out by treating with RMgR' (R, R' = Et, Bu, Hlg) in the presence of Cp 2 ZrCl 2 as a catalyst. As a result new unsaturated bi-and tricyclic organomagnesium compounds were obtained in high yields.

Alkenyl Magnesium Compounds: Generation and Synthetic Application

“…The main product 124 were generated from the cross‐cyclomagnesation of cycloalkynes and alkynes. The by‐products 122 and 123 were generated from homocyclomagnesation of alkynes or cycloalkynes, respectively (Scheme d) …”

Silver-Catalyzed Regioselective Carbomagnesiation of Alkynes with Alkyl Halides and Grignard Reagents

“…Combinations of this reaction and subsequent trapping with electrophiles or metal-catalyzed coupling provide a useful and practical method for the synthesis of multisubstituted alkenes 2 . Although a variety of transition-metal catalysts, including Zr, Cr, Mn, Fe, Fe/Cu, Ni, Cu, and Ag, have been used in this carbomagnesiation, aryl, vinyl, methyl or allyl Grignard reagents have often been employed . Primary alkyl Grignard reagents have, in some cases, been reported to work, ,,,,− , but the reaction was inefficient , and/or restricted to alkynes having a directing heteroatom group. ,,− Reactions for the introduction of secondary , or tertiary , alkyl groups to alkynes are more limited, and sterically hindered alkyl Grignard reagents are less easily accessible.…”

“…Although a variety of transition-metal catalysts, including Zr, Cr, Mn, Fe, Fe/Cu, Ni, Cu, and Ag, have been used in this carbomagnesiation, aryl, vinyl, methyl or allyl Grignard reagents have often been employed . Primary alkyl Grignard reagents have, in some cases, been reported to work, ,,,,− , but the reaction was inefficient , and/or restricted to alkynes having a directing heteroatom group. ,,− Reactions for the introduction of secondary , or tertiary , alkyl groups to alkynes are more limited, and sterically hindered alkyl Grignard reagents are less easily accessible. As a practical method for overcoming these difficulties, we herein report a new catalytic system which enables the regioselective carbomagnesiation of alkynes with secondary and tertiary alkyl iodides and commercially available i -BuMgCl in the presence of a silver catalyst (Scheme , route B). , In this reaction, the alkyl group of an alkyl halide is transferred to an alkyne carbon to give the corresponding vinyl Grignard reagents 1 , and sterically hindered alkyl Grignard reagents (RMgX) do not have to be preformed.…”