A-silyl Grignard reagents

Reactions of a-Silylated Grignard Reagents with Alkenyl Halides... 

The transformation of a silyl Grignard reagent (81, S 0.457 ppm) into a disilylmagme-sium compound (82, S 0.465 ppm) by the action of dioxan in CeDe solution, according to equation 28, could be followed in time by H NMR spectroscopy. It should be noted that the THF ligands are strongly coordinated to the Mg atom °. ... 

Figure 7 Formation of the a-silylated Grignard reagent using magnesium activated by the dry-stir method.

Generation of a-Silyl Grignard Reagents from a-Silylalkyl Halides... 

Extension of the TMM strategy to intramolecular reactions greatly expands the scope of this BCR methodology. Hie precursors are readily available, e.g. from the silyl Grignard reagent (123) and w-oxo-a,3-unsaturated substrates (equation 126). Ester- and sulfonyl-substitutedbicyclo[3.3.0]octane and bicy-clo[4.3.0]nonane systems are readily constructed in a single step from acyclic material (equations 127, 128). 2... 

The optical purity of the recovered hydrosilane indicated 70% retention of configuration in the overall process. In a similar way the reaction of methylmagnesium bromide with the silyl-cobalt complex afforded a chiral silyl-Grignard reagent (equation 27). 

Hydrolysis or condensation with allyl bromide showed retention of configuration to occur at silicon. However, products of low optical purity were obtained. It is difficult to know whether some racemisation had occurred in the silicon-cobalt bond cleavage or whether it is due to a low configurational stability of the silyl Grignard reagent. 

At this stage in the project, we decided to use a model system to try and learn more about the potential of future steps in the synthetic route. As such, the orthoester of acid 35 was formed (36 Scheme 5). Ozonolysis and addition of a vinyl Grignard reagent were not successful however, the failure of this process was possibly due to cleavage and decomposition of the orthoester. To further simplify the process, the acid was protected by reduction to the alcohol (38) and formation of the sUyl ether 39. While this was not ideal for an eventual synthetic route for reasons of step/atom/redox economy, a silyl ether would be more stable to future conditions and help determine... 

Silyl ketones are hydrolytically unstable and can be converted to the desilylated ketone by simple acid or base treatment, or used in a Peterson alkenation reaction to provide enones. They are also precursors to silyl enol ethers by rearrangement. Reaction of the /3-silyl ketone with a vinyl Grignard reagent provides a rapid entry to 2-substituted 1,3-dienes by a Peterson protocol. ... 

Trialkylsilanes are usually formed by the addition of a lithium or Grignard reagent to the silyl chloride, and thus, discussions related to the formation of the silyl acetylene bond will be kept to a minimum. Silyl acetylenes are prepared from the alkynylcopper(I) reagents in the presence of PPh3, Zn or TMEDA in CH3CN at 100°, 36-98% yield. It is interesting to note that the... 

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