Dienyl aldehydes, preparation

Brown and co-workers developed a novel homoallenyl boronate reagent 169 based on diisopropyl tartrate for the stereoselective homoallenylation of aldehydes 170. The reagent 169 was prepared via homologation of the corresponding allenyl boronate or the alkylation of halomethyl boronate with allenyl Grignard similar to those reported in Scheme 26. The allyl boronate 169 upon reaction with aldehydes furnished the dienyl alcohols 172 with high ee (Scheme 28) <1996JOC100>. 

This method can also be applied to complexes of conjugated trienes. The uncomplexed double bond may be constructed within the complex via Wittig olefination. Cyclopropanation of the uncomplexed double bond of the resulting tricarbonyliron-triene complexes and oxidative decomplexation leads to dienylcyclopropane products. In this manner chiral dienyl-cyclopropanes 4 and 5 were prepared in high enantiomeric excess (> 90% ee) starting from optically active tricarbonyliron-hexatriene complexes 3 obtained from chirally modified sorbic aldehyde complexes. 

In more recent years, the nucleophilic and electrophilic epoxidations of a-hydroxy dienyl sulfoxides as versatile routes to highly functionalized sulfinyl and sulfonyl tetrahydrofurans have been studied in depth.Fernandez de la Pradilla s group has reported that a-hydroxy dienols bearing chiral sulfoxides (267), prepared from the reaction of chiral dienyl sulfoxide lithium compounds with freshly distilled aldehydes, were subjected to epoxidation using m-CPBA as oxidant, leading to monoepoxides 269 as main products in low to moderate yields and low stereochemical selectivities subsequently, monoepoxides 269 were treated with catalytic CSA to afford 96-99% yields of predominantly 2,5-cis mixtures of sulfonyl dihydrofurans 270 (Scheme 4.86). These highly functionalized sulfonyl tetrahydrofurans were also obtained in a... 

Methyl and ethyl-selenuranes, prepared fnxn trimethyl-, methyldi[dienyl- and ethyldiphenyl-selenoni-um salts, respectively, and BuHDK in DMSO, react with aromatic aldehydes and keumes, including those that are a,p-unsaturated, to produce the corresponding epoxides in go yields (Scheme 59). Metal-... 

Allenyl a,/3-unsaturated isoprenoid aldehydes can be prepared in high yields by the rearrangement of propargyl enol carbonates (Scheme 28). The dienyl propargyl carbonate was prepared from /3-ionone and subjected to Pd-catalyzed rearrangement. The allenyl alde-... 

In Scheme 1 is shown the preparation of the dienyl glycosides by reaction of acetobromoglucose with the sodium salt of malonaldehyde followed by Wittig olefination of unsaturated aldehydes, which provided... 

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