Magnesium exchangeability

A similar influence of the lithium-magnesium exchange is documented for tetrahydroisoquino-lines, derived from chiral oxazolines (see Section 1.3.2.3.3.2 ). The tuning by magnesium bromide also serves well in the carbonyl addition of lithiated tetrahydro-2-isoquinolinecarboxy-late24, prepared by the Katritzky protection/activation method27,28. 

A New Improved Synthesis of Tricycle Thienobenzazepines Apphcation of chemistry recently developed by Knochel" combined with the well-described halogen dance (HD) reaction, allowed preparation of our key intermediate A in only three synthetic transformations (Scheme 6.4). In this respect, treatment of 2-bromo-5-methylthiophene with hthium diisopropylamide followed by dimethylformamide afforded aldehyde 11 in good yield, lodo-magnesium exchange with conunercial 4-iodo-3-nitro anisole followed by reaction with 11 afforded the thiophene catbinol 12. Dehydroxylation of 12 provided our key intermediate A which presented the requisite functionality to examine our approach to the construction of the seven-member ring system. 

This iodine-magnesium exchange can also be performed with heterocyclic iodides, such as the functionalized pyridine 16 [21] or the iodouracil derivative 17 (Scheme 2.5) [22]. In both cases, the intermediate organomagnesium reagent can... 

Remarkably, halogen-magnesium exchange can also be extended to aryl and heteroaryl bromides [24, 25], Thus, the functionalized aryl bromides 28 and 29 (Scheme 2.7) were converted, at 0 °C and at —30 °C, respectively, into the corresponding Grignard reagents. After treatment with CuCN, the copper derivative 30 and 31 were obtained. Subsequent treatment with typical electrophiles such as benzoyl bromide or allyl bromide furnished the products 32 and 33, in 70 and 80% yields. 

Matsui Y. and Nishizawa O. (1974). Iron magnesium exchange equilibrium between coexisting synthetic olivine and orthopyroxene. Amer. Jour. Set, 267 945-968. 

The functionalized arylzinc reagents are best prepared either starting from an aryllithium obtained by halogen-lithium exchange followed by a low-temperature (-80°C) transmetalation with ZnBrj or by performing an iodine-magnesium exchange reaction. The latter reaction tolerates temperatures up to -30°C and is more convenient for industrial applications. ... 

Aldol reactions of simple amide enolates give poor stereoselection. Stimulated by the interest in /3-lactams, the stereochemistry of aldol reactions of chiral magnesium enolates of /3-lactams has been studied . The best results have been obtained with 6,6-dibromopenams 85 (equation 108). After bromine-magnesium exchange with MeMgBr,... 

In 1931 Pr6vost reported the reaction of cinnamyl bromide (13) to cinnamyhnagnesium bromide (14), which was the first example of a bromine-magnesium exchange reaction (equation 10). ... 

The presence of bis[2-(A,A-dimethylamino)ethyl]ether allows a selective halogen-magnesium exchange of iodo- and bromoaromatics at ambient temperature using iso-propylmagnesium chloride. Sensitive carboxylic ester and cyano groups are well tolerated (equations 29 and 30). ... 

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