Reagent self-protection

Persistency can be conferred on the stannenes by steric protection to hinder self-reaction. For example, bis(2,4,6-triisopropylphenyl)(fluorenylidene)stannene can be prepared as the ether complex (6n9Sn = 288, <513C = 133.9, UV Amax = 542 nm), as violet crystals, by dehydrofluorination as shown in Scheme 21.573-576 At room temperature, it slowly converts into the head-to-tail dimer. Protic reagents and methyl iodide add across the double bond, and the bond is reduced by lithium aluminum hydride. 

One way to make it is to add a Grignard reagent twice to ethyl formate. But, of course, a ketone-containing Grignard is an impossibility as it would self-destruct, so an acetal-protected compound was used. 

Synthesis of aldehydes and ketones. This substance can function as a protected cyanohydrin of formaldehyde in an extension of Stork and Maldonado s synthesis of ketones from aldehydes, RCHO —> RCOR, by way of cyanohydrins (4, 300-301). Thus the anion of 1, generated with LDA, does not undergo self-condensation, but can be alkylated the product on hydrolysis gives the homologous aldehyde of the alkyl halide. Thus the reagent serves as the latent anion of formaldehyde, HC=0. An example is shown in equation (I). 

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