Alkyl conjugates, development indicators

Asymmetric conjugate addition of a-substituted-oc-cyanoacetates 77 to acetylenic esters under phase-transfer conditions is somewhat of a challenge, because of the difficulty encountered in controlling the stereochemistry of the product. In addition, despite numerous examples of the conjugate additions to alkenoic esters, no successful asymmetric conjugate additions to acetylenic esters have been reported to date. In this context, Maruoka and coworkers recently developed a new morpholine-derived phase-transfer catalyst (S)-76 and applied it to the asymmetric conjugate additions of a-alkyl-a-cyanoacetates 77 to acetylenic esters, as indicated in Table 5.11 [40], In this asymmetric transformation, an all-carbon quaternary stereocenter can be constructed with a high enantiomeric purity. 

Conditions have been developed that allow the alkyl groups in organoboranes to be alkylated by certain conjugated olefins and reactive halides. Typical a,/3-unsaturated carbonyl compounds such as acrolein and methyl vinyl ketone (see Scheme 3.7 for other examples) alkylate organoboranes. Evidence has been developed that indicates that the alkylation proceeds via free-radical intermediates. It therefore cannot be assumed that such alkylations will always proceed with the retention of configuration that is characteristic of oxidations and carbonyla-tions of organoboranes. ... 

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