Benzyl-Grignard reagents

Unfortunately this route gives only a 40% yield IJ. Amer. Cham. Soc 1951, 73, 3237) in the Grignard reaction, largely because benzyl Grignard reagents easily give radicals which polymerise. In any case, it s poor tactics to chop off carbon atoms one at a time, and a better disconnection would be ... 

Very recently, a dry-stir method for the mechanical activation of commercial magnesium turnings was reported16. The procedure is also excellently suited for the preparation of allylic and benzylic Grignard reagents (Table 1, method B). 

Zinc bromide promoted addition of a functionalized benzyl Grignard reagent to the a,/ -unsat-urated y-lactone, 3-(4-methylphenylsulfinyl)-2(5//)-furanone, via a zinc-chelated intermediate, gave, after several synthetic steps, (-)-podorhizon with 95% ee18. 

C. Reactions of Phosphoric and Phosphinic Acid Derivatives.—The optically active phosphinate ester (90) has been shown to react with benzyl Grignard reagents or lithium anilide with inversion of configuration. Oxidation of... 

In the similar reaction of 2-pyridyi benzylic sulfoxides with benzylic Grignard reagents, the incoming benzylic group seemed to couple pref-... 

As shown in Scheme 78, with or without zinc chloride, benzylic Grignard reagents couple with vinyl bromide to form allylbenzene derivatives in high ee (188). This method has been used to prepare optically active allylsilanes in up to 95% ee. Vinylic bromides with E configurations lead to the E allylsilanes with high ee, and Z bromides lead to Z allylsilanes with lower ee. 

Coles, S. J. Mellor, J. M. El-Sagheer, A. H. Salem, E. E.-D. M. Metwally, R. N. Reaction of benzyl Grignard reagents with trifluoroacetyl-dihydropyrans and other cyclic /3-alkoxy a,/ -unsaturated trifluoromethyl ketones. Tetrahedron 2000, 56, 10057-10066. 

Reactions of allylic and benzylic Grignard reagents with alkyl nitro compounds can, under the right conditions, provide an acceptable route to nitrones [11]. Lack of regio- and stereoselectivity may be a problem, though the former can be controlled to some extent by varying the acid used for protonation, e.g. 

The carbinol precursor of propoxyphene is made by treating the Mannich base 21a with a benzyl Grignard reagent. The major (a) diastereoisomer 21b is separated, resolved with (+)-camphor-10-sulfonic acid, and finally acylated to yield the active drug. Pyrrolidino analogs of propoxyphene are more potent than the parent (acetate, 2 x, propionate,1 x pethidine in mice),(51) while the halogenated acetates 22 (X = F or Cl) have similar activities to morphine in mice.(58) Replacement of terminal phenyl of propoxyphene by 2-pyridyl achieves a potency rise, as occurs also in the cyclic analog 23/59 ... 

Cyclopropyl phenyl sulfones. 3-Bromo-l-(phenylsultonyl)-l-propene (1), prepared as shown, reacts with allyl, propargyl, aryl, and benzyl Grignard reagents to give (E)-2-substituted cyclopropyl phenyl sulfones (2) in moderate to good yield. This reaction is not observed with alkyl Grignard reagents. 

Diphenylacetoin, a hydroxy ketone, has been prepared in 45-60% yield by the action of benzyl Grignard reagent on phenylacetaldehyde cyanohydrin. ... 

Two notable total syntheses of pentacyclic triterpenoids have been reported. In the synthesis of ( )-germanicol (115), the tricyclic ketone (116) was conceived as a general intermediate which embodies the features of rings A, B, and c of many triterpenoids. Conjugate addition of the benzyl Grignard reagent to the... 

Benzylethyl silicon dichloride is obtained as above, using the benzyl Grignard reagent. To avoid formation of too much dibenzyl, the reaction is carried out at 0° C. The two products obtained are benzylethyl silicon diehloride and dihemylethyl silicon chloride. The former is a mobile, fuming liquid, B.pt. 160° C. at 100 mm. 

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