Stereodivergent Synthesis of Enantioenriched 4-Hydroxy-2-cyclopentenones
作者:Gurpreet Singh、Angelica Meyer、Jeffrey Aubé
DOI:10.1021/jo402539p
日期:2014.1.3
Protected 4-hydroxycyclopentenones (4-HCPs) constitute an important class of intermediates in chemical synthesis. A route to this class of compound has been developed. Key steps include Noyori reduction (which establishes the stereochemistry of the product), ring-closing metathesis, and simple functional group conversions to provide a set of substituted 4-HCPs in either enantiomeric form.
Optically pure 1,3-diols from (2R,4R)- and (2S,4S)-1,2:4,5-diepoxypentane
作者:Scott D. Rychnovsky、George Griesgraber、Sam Zeller、Donald J. Skalitzky
DOI:10.1021/jo00017a032
日期:1991.8
Optically pure (> 97% ee) (2R,4R)-1,2:4,5-diepoxypentane (1) and its enantiomer can be prepared in three steps from 2,4-pentanedione without the need for chromatographic purification. Diepoxide 1 is an efficient precursor to a wide variety of optically pure syn and anti 1,3-diols. Reaction with excess nucleophile gives symmetric[GRAPHICS]anti 1,3-diols in good yield. Reaction with a slight excess of alkyllithium under Ganem's conditions gives the monoepoxides 5 in good yield. Addition of a second nucleophile to monoepoxide 5 gives asymmetric anti 1,3-diols. Mitsunobu inversion of monoepoxide 5 followed by addition of a second nucleophile gives syn 1,3-diols. Optically pure syn and anti 1,3-diols are available from diepoxide 1 in one to three steps and good overall yield.
Enantioselective Synthesis of (+)-Obolactone Based on a Symmetry-Breaking Wacker Monooxidation of a Diene
作者:Patrick Walleser、Reinhard Brückner
DOI:10.1021/ol400232m
日期:2013.3.15
A concise synthesis of the dihydro-alpha-pyrone/dihydro-gamma-pyrone natural product (+)-obolactone (13) is disclosed. The dienediol acetonide 23 (>= 97% ee) was obtained from 1,5-dichloropentane-2,4-dione in four steps. A Wacker monooxidation of 23 furnished the monoketone 24 in 64% yield. The OH group of the ensuing dihydro-gamma-pyrone 31 was esterified under Mitsunobu conditions with cinnamic acid (-> 80% inversion and 20% retention of configuration). A ring-closing metathesis formed the dihydro-alpha-pyrone moiety of the target in the terminating step.