Preparation of (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate via Novozym-435® catalyzed desymmetrization of cis-3,5-Diacetoxy-1-cyclopentene
2018
Putta, Shekhar | Reddy, Annem Mallikarjun | Sheelu, Gurrala | Reddy, B.V Subba | Kumaraguru, Thenkrishnan
Photooxidation of cyclopentadiene has been carried out in methanol using white light of LED lamp, rose bengal as photo initiator, and compressed air at 0 °C. Under conditions of [thiourea] ≫ [cyclopentadiene], the consumption of thiourea follows a pseudo-first-order reaction kinetics with half life of 75 ± 10 min; corr. coeff. r = 0.989. Slow addition of the monomer and maintaining excess thiourea concentration in reaction mass improves the yield. cis-3,5-Dihydroxy-1-cyclopentene is acetylated without isolation to obtain cis-3,5-Diacetoxy-1-cyclopentene of high purity (>99%) with overall isolated yield of 30%. Desymmetrization of the diacetate to (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate has been carried out via enzymatic transesterification with methanol in methyl tert-butyl ether (MTBE) at 5 °C using Novozym-435®. The enantiomerically pure monoacetate (e.e. >99%) was obtained in 95% isolated yield. The recovered enzyme was reused for more than 10 times without loss in yield and selectivity. The entire protocol does not require purification of final product by chromatography.
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