Asymmetric Dihydroxylations of 1-Substituted (<i>E</i>)- and (<i>Z</i>)-3-Methylpent-2-en-4-ynes: Full Compliance with the Sharpless Mnemonic Re-established and Embellished
Asymmetric dihydroxylations ("ADs") of the pentenynyl chlorides (E)- and (Z)-1 or the pentenyne-based ester (Z)-3 in the presence of (DHQ)(2)-containing ligands delivered diol stereoisomers (2R,3S)-2, (2R,3R)-2, and (3S,4R)-4, respectively. The ADs of pentenynyl ethers (E)-10 and (Z)-12, respectively, have the same stereochemical preference under analogous conditions; these reattributions correct previous reports of the contrary. The Sharpless mnemonic rationalizes all these results implying that each substrate prefers a Sharpless/Norrby instead of a Chapleur orientation in the transition state.
Asymmetric Dihydroxylations of Enynes with a Trisubstituted C═C Bond. An Unprecedented Route to γ-Lactone Building Blocks with a Quaternary Stereocenter
comprehensive set of hydroxylactone building blocks (4R,5R)-, (4R,5S)-, (4S,5R)-, and (4S,5S)-5a, Sharpless asymmetric dihydroxylations of allylicchlorides (E)- and (Z)-9 were performed. They delivered the four stereoisomers of diol 10 with up to 92% ee and absolute configurations, which were proven to be in accordance with the Sharpless mnemonic.