Ethers, diethyl oxidative deprotection

Yamauchi et al. completed an ex-chiral pool synthesis of a samin-type lignan, Scheme (38) [102]. The diprotected tetraol 230 was obtained from Z-glutammic acid by a 15 step procedure in 7-8% overall yield [103]. The diprotected tetraol 230 was treated with boron trifluoride diethyl etherate in dichloromethane to give the tetrahydrofuran 231 in 84%-87% yield. After deprotection with tetrabutylammonium fluoride, the resulting diol was oxidized by dihydridotetrakis(triphenylphospine)ruthenium(II) to provide two lactones 232 and 233 in a ratio of 2 1. Lactone 232 was transformed in samin-type lignan 234 by diisobutylaluminium hydride reduction in 70% yield. 

Theil et al. developed a method for chemoenzymatic synthesis of both enantiomers of cispentacin [89]. frans-2-Hydroxymethylcyclopentanol, obtained by the sodium borohydride reduction of ethyl 2-oxocyclopentanecarboxylate, was monosilylated with tert-butyldimethylsilyl (TBDMS) chloride to afford 55. Lipase PS-catalysed transesterification with vinyl acetate in /erf-butyl methyl ether furnished the ester 56 and the alcohol 57. The deacetylated 58 was obtained by the Mitsunobu reaction with phthalimide, triphenylphosphine and diethyl azodicarboxylate (DEAD) to furnish the cis oriented 59 with inversion of configuration (not retention as mentioned in the original article) (Scheme 9). Desilylation, Jones oxidation and subsequent deprotection with aqueous methylamine gave the ( R,2S) enantiomer 5 [89]. The (15, 2/f) enantiomer was prepared by the same route from the silyl alcohol 57. 

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