Furans in synthesis. 11. Total syntheses of (.+-.)- and (-)-fastigilin C

Enantioselective preparation of (R) and (S)-3-hydroxycyclopentanone by kinetic resolution

“…This is in line with the earlier observation that only cyclopentanol derivatives with large or many substituents give high E value in kinetic resolution [21][22][23][24][25][26][27][28][29][30][31][32][33]. Those with small and few substituents, such as cyclopent-4-ene-1,3-diyl diacetate (80% yield, 20.5% ee) [34], cyclohex-2-en-1-yl acetate [35], 4-hydroxycyclopent-2-en-1-one (E = 11) [36], 4-hydroxy-2-methyl-2-cyclopentenone (60% yield, 60% ee) [37], 3-bromocyclopent-2-enol [38] give less enantiopure products. An exception is the meso compounds [43][44][45][46][47][48][49], however here the stereo differentiation is based on a different principle.…”

“…A general trend observed is that derivatives with large substituents are readily resolved [21][22][23][24][25][26][27][28][29][30][31][32][33], while simple compounds similar to our target molecule tend to give low E values [34][35][36][37][38].…”

Enantioselective Total Synthesis of a trans‐Hydrindane Rings/Side‐Chain Building‐Block of Vitamin D − Asymmetric Induction in an Acid‐Catalyzed Conjugate‐Addition Reaction

“…[27,28] A high degree of induced diastereoselectivity has also been reported in the case of the TrSbCl 6 (Tr ϭ trityl) catalyzed addition of an achiral propionate-derived ketene acetal to optically active 4-methoxy-2-methylcyclopent-2-en-1-one. [29] Analysis of various enantioselective approaches to compound 8 and some preliminary experiments focused our attention on optically active ketene acetals bearing a protected diol functionality, of general structure ii (Scheme 2).…”

A new and efficient chemoenzymatic route to both enantiomers of α′-acetoxy-α-methyl and γ-hydroxy-α-methyl cyclic enones

“…The combined (S)-4 (60% ee) batches were exposed again to b,b,b-trifluoroethyl butyrate and PPL in ether to provide (S)-4 in a 52% isolated yield and >98% ee. 6 In our ongoing investigations, we have published several papers concerning the Mn(OAc) 3 -mediated direct acetoxylation and acyloxylation of enones and aromatic ketones followed by the enzymatic-and fungusmediated resolution of acyloxy enones to obtain enantiomerically pure a-hydroxy ketones. 7 Due to the multi-functional nature of chiral a 0 -hydroxy-a-methyl, a 0 -acetoxy-a-methyl, and c-hydroxy-a-methyl cyclic enones 1-4, they can take part in several stereoselective transformations, which led us to explore a chemoenzymatic method for obtaining them in their enantiomerically pure forms.…”