Conversion of isoxazolines to β-hydroxy esters. Synthesis of 2-deoxy-D-ribose

Pentafulvene for the Synthesis of Complex Natural Products: Total Syntheses of (±)‐Pallambins A and B

“…Most commonly,t hey are converted into b-hydroxy nitriles using either TMSCl/NaI [13a] or NaSEt [13b] or reduced to bhydroxy amines.A fter extensive experimentation, including transition-metal-catalyzed couplings,radical dehalogenations, or substitution reactions with vinyl anions,n oe ffective functionalization of 19 could be established. Additionally, when 19 was converted into the corresponding b-hydroxy nitrile using TMSCl/NaI, reduction to the aldehyde was found to be exceedingly difficult under av ariety of conditions (iBu 2 AlH, iBu 2 AlH·SMe 2 , [14a] Red-Al, Li(iBu) 2 (nBu)AlH, [14b] Ra-Ni/NaH 2 PO 2 [14c] or Ra-Ni/formic acid [14d] )a nd alternative approaches were deemed necessary.T hus,b romide-methoxide exchange, [15] followed by Ra-Ni-mediated hydrogenolysis of the NÀOb ond smoothly provided ester 21 in 91 % overall yield (Scheme 3). While ester reduction with iBu 2 AlH led to decomposition of both starting material and product, the use of non-Lewis-acidic Li(iBu) 2 (nBu)AlH (generated from iBu 2 AlH and nBuLi) [16] cleanly provided the corresponding diol in 89 %yield.…”

Three-Dimensional Heterocycles: New Uracil-Based Structures Obtained by Nucleophilic Substitution at the sp2 Carbon of Bromoisoxazoline

“…The bromonitrile oxide 3 is generated in situ in an AcOEt/NaHCO 3 solution from the corresponding bromoxime 2 [14], which is easily prepared by treating glyoxylic acid with hydroxylamine hydrochloride in the presence of bromine at 5 °C in dichloromethane [15]. Using N-benzoyl-2,3-oxazanorborn-5-ene (1) as dipolarophile, the 1,3-dipolar cycloaddition reaction smoothly occurs affording the regioisomeric compounds 4a,b in 45% and 44% yields, respectively, which are easily isolated upon chromatographic separation (Scheme 3).…”

Pentafulvene for the Synthesis of Complex Natural Products: Total Syntheses of (±)‐Pallambins A and B

“…Additionally, when 19 was converted into the corresponding β ‐hydroxy nitrile using TMSCl/NaI, reduction to the aldehyde was found to be exceedingly difficult under a variety of conditions ( i Bu 2 AlH, i Bu 2 AlH⋅SMe 2 ,14a Red‐Al, Li( i Bu) 2 (n Bu)AlH,14b Ra‐Ni/NaH 2 PO 2 14c or Ra‐Ni/formic acid14d) and alternative approaches were deemed necessary. Thus, bromide–methoxide exchange,15 followed by Ra‐Ni‐mediated hydrogenolysis of the NO bond smoothly provided ester 21 in 91 % overall yield (Scheme ). While ester reduction with i Bu 2 AlH led to decomposition of both starting material and product, the use of non‐Lewis‐acidic Li( i Bu) 2 (n Bu)AlH (generated from i Bu 2 AlH and n BuLi)16 cleanly provided the corresponding diol in 89 % yield.…”