Vinyl Grignard reagent

Synthesis The vinyl anion synthon can either be the vinyl Grignard reagent or the acetylide arrion, in which case the synthesis becomes ... 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

Geranyl acetones also reacts with vinyl Grignard reagent to produce nerohdol directly (192). 

This procedure illustrates a general method for the preparation of 2-hydroxybicyclo[3.2.0]heptanes by copper(I)-catalyzed photobicyclization of 3-hydroxy-1,6-heptadienes, and a general route to the requisite dienes from allyl alcohols by conversion to 4-pentenals and treatment of the latter with vinyl Grignard reagents. 

Further utility of the Andersen sulphoxides synthesis is demonstrated by the preparation of optically active unsaturated sulphoxides which were first prepared by Stirling and coworkers359 from sulphinate 276 and the appropriate vinylic Grignard reagents. Later on, Posner and Tang360 prepared in a similar way a series of ( )-l-alkenyl p-tolyl sulphoxides. Posner s group accomplished also the synthesis of (+)-(S)-2-(p-tolylsulphinyl)-2-cyclopentenone 287, which is a key compound in the chiral synthesis of various natural products361 (equation 159). 

Alkenyl sulfoxides (42 and 43) were first prepared in optically active form by Mulvaney and Ottaviani , described in an article overlooked by most workers in the field, and a year later by Stirling and coworkers through the reaction of the appropriate vinyl Grignard reagent with sulfinate ester 19. Both groups studied the addition of nucleophiles to the carbon-carbon double bond . More recently, Posner and coworkers reported a similar synthesis of ( )-l-alkenyl sulfoxides, e.g. 44 and In the synthesis of 45,... 

Moreover, the authors were able successfully to apply this process to the synthesis of the antibiotic (+)-CP-263,114 (2-912) (Scheme 2.203) [454]. Transformation of the bromide 2-908 into the vinyl Grignard reagent 2-909, followed by addition to the ketone 2-910, led to the bridged carbocyclic compound 2-911 which was then transformed into the target compound within a few steps. 

Substituted indoles from the reaction of ort/jo-substituted nitroarenes and vinyl Grignard reagents. 

From organyltellurenyl halides and vinylic Grignard reagents... 

Ham et al. [60] used an unselective attack of a vinyl Grignard reagent on the iST-benzoyl-protected phenylalaninal 92 to generate alcohols 93 (Scheme 25). A tmns-selective, Pd(0)-catalyzed oxazoline formation starting from the homoallylic amide 93 was subsequently employed to build up the (S)-configuration at carbon atom C-3 of oxazoline 94. 

Reaction of vinyl Grignard reagents with a-halo ketones. Vinylmagnesium bromide or vinyllithium (2 equivalents) reacts with a-halocycloalkanones to give 1,2-divinylcycloalkanols, used in oxy-Cope rearrangements for synthesis of large ring ketones (c/ 7, 302-303 8, 412 414).8 Examples ... 

Nucleophilic attack by the vinyl Grignard reagent leads to tertiary alcohol 8 11 Grignuril reagents react with formaldehyde to give primary alcohols and with other aldehydes to give secondary alcohols, whereas ketones are transtormed into tertiary alcohols. 

Vinyl Grignard reagent reacts with the aldehyde function in the open-chain form of compound 6. leading initially to diol 25 with a diastereoselectivity of 71 2 antr.syn). The diasteromeric alcohols atn be separated after silylation to 7, but this is unnecessary since both isomers lead to the same product in the subsequent reaction. 

As discussed in connection with olefin-coupling reactions and shown in Fig. 4, the coupling of vinyl Grignard reagents is stereospecific and dependent upon the transition metal catalyst used (32, 33). The dimerization of ethylene, shown in Fig. 6, was also shown to produce primarily the terminal olefin 1-butene (35). The size of the metal has also been shown to influence the course of the catalyzed oligomerization reactions of butadiene. When bis-(ir-allyl) metal complexes are used as... 

Vinyl Grignard reagents are known, although they are a bit more difficult to prepare than simple alkyl Grignard reagents. Either pair of reagents will work. 

The vinyl Grignard reagent was used with Cu(I) catalysis and the reduction of both ester and ketone was achieved with UAIH4. The stereoselectivity was excellent and 75 could easily be separated from the minor equatorial alcohol. In the next chapter we shall revisit both the use of copper in getting regioselectivity and the stereoselectivity of such reactions. 

The divergent epoxide stereoisomers are available via epoxidation of the (E)- or (Z)-vinylsilanes, which in turn are prepared by (1) addition of an (/. )-vinyl Grignard reagent to the chlorosilacyclobutane, or (2) partial hydrogenation of an alkynylsilacyclobutane, respectively (Scheme 37). 

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