Alkene aldehydes from diene alcohols

In Hanessian s approach to avermectin discussed in Section 3.1.11.4.1, the Julia coupling was used for the trisubstituted alkene and the diene portion of the molecule. The sulfone (439) was deprotonated with Bu"Li and the aldehyde (440) added to it to obtain a 47% yield (77% based on recovered sulfone) of -hydroxy sulfones (equation 103). The alcohol was converted to the chloride and the reductive cleavage carried out with sodium amalgam in 35% yield. The desired diene was the only detectable isomer (441). From the examples cited, it is apparent that the synthesis of ( , )-dienes by the Julia coupling is an extremely successful process, in terms of both yield and selectivity. 

When phenyl(trimethylsilyl)diazomethane (20) is pyrolyzed in the gas phase, typical reactions of carbene 21 can be observed (see Section III.E.4). However, copyrolysis with alcohols or carbonyl compounds generates again products which are derived from silene 2239,40 (equation 6). Thus, alkoxysilanes 23 are obtained in the presence of alcohols and alkenes 24 in the presence of an aldehyde or a ketone. 2,3-Dimethylbuta-l,3-diene traps both the carbene (see Section ni.E.4) and the silene. 

Commercial RuC13 xH20 is widely used as a catalyst (see references 3 and 2320 for details of earlier studies). Examples include the oxidation of amines and alcohols,2321 the production of glycol esters from synthesis gas,2322 and the generation of 1,3-diol derivatives from reaction of dienes and alkenes with aldehydes and carboxylic adds.2323... 

PdCE-catalyzed addition reaction of allyl chloride to alkynes is explained by chloropalladation of a triple bond, followed by insertion of the double bond of allyl chloride to generate 43. No jr-allyl complex is formed from allyl chloride and PdCl2. The final step is elimination of /3-Cl to afford 1-chloro-1,4-diene 44 with regeneration of Pd(ll) [37]. As another example, the Pd(0)-catalyzed Heck reaction of vinyl acetate affords stilbene in this reaction, the primary product is /3-phenylvinyl acetate (45), which reacts again with iodobenzene, and the last step is elimination of /S-OAc to give stilbene. At the same time, Pd(II) is generated, which is reduced to Pd(0) in situ [38]. However, elimination of /3-heteroatoms is not always faster than that of j8-H. For example, the Heck reaction of allyl alcohol with iodobenzene proceeds by preferential elimination of /3-H from the insertion product 46 to afford aldehyde 47, and no elimination of /3-OH from the same carbon occurs to give the alkene 48 [39,40]. 

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