Organomagnesium reagents derivatives

Since it has been reported (57) that transition metal halides will catalyze the RMgX/RX exchange, many of the so-called Kharasch reactions may actually involve transient organomagnesium reagents derived from such processes, and Slaugh has cited the production of bicyclo[3.1.0]hexane from 1,3-dibromocyclohexane and cyclohexene from 1,2-dibromocyclo-hexane. 

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... 

Chiral organomagnesium amides form an efficient method to realize enantioselective conjugate addition. Sibi and Asano have reported the Michael addition of cr-bound magnesium reagents derived from bisoxazolines to enamidomalonates (equation 41). The enantioselectivity of the addition is discussed in Section El. This method allows the preparation of chiral -amino acid derivatives. ... 

Cuprates derived from copper thiophenoxide and 3 mol equiv. of organomagnesium reagent were also shown to undergo conjugate addition with P-monosubstituted enoates.86 The large molar excess of RMgX is necessary and ether is the preferred solvent for the reaction (equation 42). The results with di-substituted enoates have not been reported, and should provide a further test of the utility of this reagent. 

Copper(i) catalysis of the addition of organomagnesium compounds to alkynes has been observed, but stoichiometric organocopper reagents, derived from organomagnesium compounds, are more effective in the absence of other activating features [4],... 

N-Acyl-2,3-dihydro-l,4-benzothiazines and the related phenothiazines react with both organolithium and organomagnesium reagents to give the / -dicarbonyl derivative 116, indicating that the N-acyl derivatives may have a role to play as useful acylating agents.157 Mechanistic studies have provided novel explanations for this behavior and that of the related 1-oxides and 1,1-dioxides (117).158... 

Chiral amines have been transformed into chiral imines RCH=NG, which are usually in equilibrium with the tautomeric enamines. These enamines undergo asymmetric alkylations, and the best results are often obtained with ethers 1.58 or with valine derivatives 1.59 (R = i-Pr, R = tert-Bu) [169, 173,253] in the presence of bases. Enamines, lithioenamines and zinc enamines derived from imines are very potent Michael donors that often participate in highly stereoselective reactions [161, 162, 169, 173, 254, 257, 260, 262, 267], Chiral imines can suffer very selective addition reactions of organomagnesium reagents [139, 253, 254] and allyl-metals [154, 258]. They also suffer stereoselective Ti-catalyzed silylcyanation [268], Strecker reaction [266], and [2+2] or [4+2] cydoadditions [131, 256, 263], When the reaction produces an imine product, the chiral auxiliary is recovered after acidic hydrolysis. However, when an amine is obtained as the product, as is often the case from phenethylamine derivatives, the chiral residue is cleaved by hy-drogenolysis. In such cases, the chiral amine is not, strictly speaking, a chiral auxiliary. But these processes will be discussed anyway because of their importance in asymmetric synthesis. 

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