Novel approach to stereoisomerically full set of optically pure 2,3-epoxyesters from tartaric acids

Novel Approach to the Zaragozic Acids. Enantioselective Total Synthesis of 6,7-Dideoxysqualestatin H5

“…In the first, dimethyl tartrate ( 20 ) was protected as its mono-THP derivative 21 (Scheme ). Chemoselective reduction of the ester moiety α to the hydroxy group in 21 was best achieved using BH 3 ·SMe 2 in the presence of catalytic NaBH 4 to give an inseparable mixture (3:1) of the 1,2 and 1,3-diols . After selective protection of the primary alcohol as its TBDPS ether, the diprotected alcohol 22 was isolated in 50% yield by column chromatography.…”

Application of Chiral 2-Isoxazoline for the Synthesis of syn-1,3-Diol Analogues

“…Either syn-or anti-1,3-diol could be prepared from enantiomerically pure β-hydroxy ketone via β-hydroxy directed carbonyl reduction in Evans' 3 or Prasad's [4][5][6][7][8][9][10][11] method. Narasaka-Prasad reduction of the δ-hydroxy-β-keto-ester derived from a β-hydroxy ester [12][13][14][15][16][17][18][19][20][21][22][23] is widely used to prepare t-butyl (3R)-3,5-O-isopropylidene-3,5-dihydroxyhexanoate (Scheme 1a) [24][25][26][27][28][29][30][31][32][33][34][35][36][37] , which is a building block for synthetic statins, [38][39][40][41] though enzymatic synthesis [42][43][44][45][46][47][48] of chiral β-hydroxy-δ-lactone moiety or its equivalents, pioneered by Wong, 42 is equally competitive. Here, we report the pr...…”

First Unambiguous Characterization of a Novel RO-BH2 Intermediate by 1H{11B} and 1H{13C,11B} NMR Spectroscopy. Proof of Boron−Carbonyl Interaction through Innovative Use of NMR Techniques

“…Reaction of BH 3 ·THF with hydroxy groups is well documented and widely believed to yield species containing an O-BH 2 functionality. , Coordination of nitrogen stabilizes such species, and a few cases have been reported where such compounds were characterized. For example, 11 B NMR chemical shift arguments, 11 B NMR multiplicities, and IR stretching frequencies have been used to show that stable compounds comprising a cyclic O-BH 2 ← N structure are formed when BH 3 ·THF reacts with 8-hydroxyquinoline derivatives. , Equivalent five- and six-membered rings comprising an O-BH 2 ← O unit, where the BH 2 group is stabilized by the weaker interaction with an oxygen atom of a carbonyl group, have been proposed as intermediates, but so far none of these proposed structures has been verified by spectroscopy. In this paper we report on the first full characterization of an intermediate 2 using NMR spectral through-bond correlation experiments to prove the presence of a cyclic O-BH 2 ← OC unit.…”