Stereochemistry of crotylboronate additions to .alpha.,.beta.-dialkoxy aldehydes

Abstract

Errors are reported as standard deviations. 6Average of two experiments. c Average of three experiments.Fund, administered by the American Chemical Society, and in part by a generous grant from the Humphrey Chemical Company, North Haven, CT.

Cornforth–Evans Transition States in Stereocontrolled Allylborations of Epoxy Aldehydes

“…For less electronegative groups X a similar minimization of 1,3 syn ‐pentane interactions should be realized in the anti ‐PFA TS [ TS‐B cis ( a ‐PFA) ] leading to a 2,3‐ syn ‐3,4‐ syn stereochemistry . This divergent interplay between electrostatic, steric and hyperconjugative contributions could account for the poor stereocontrol sometimes found for allylboration of polar aldehydes …”

A Stereoselective Synthesis of Dihydrosphingosine

“…The commercially available palmityl alcohol (3) was converted into the corresponding aldehyde, which on treatment with (ethoxycarbonylmethylene)triphenylphosphorane in THF under reflux gave the Wittig product 4 in 89% yield. Compound 4 was subjected to DI-BAL-H reduction to furnish the corresponding allylic alcohol 5 [8] in 92% yield. The dihydroxylation of olefin 5 with osmium tetraoxide and potassium ferricyanide as co-oxidant in the presence of 1,4-bis(dihydroquinidin-9-O-yl)-phthalazine [(DHQD) 2 PHAL] ligand under the Sharpless asymmetric dihydroxylation reaction conditions [9] gave the (2R,3R)-triol 6 in excellent yield, with [α] D 20 ϭ ϩ7.2 (c ϭ 1.0, CHCl 3 ).…”

“…47Ϫ48°C (ref. [8] 46Ϫ48°C). Spectroscopic data (IR, 1 H NMR, mass) are in full agreement with those described.…”

“…Spectroscopic data (IR, 1 H NMR, mass) are in full agreement with those described. [8] (2R,3R)-Octadecane-1,2,3-triol (6): To a mixture of K 3 Fe(CN) 6 (4.14 g, 12.6 mmol), K 2 CO 3 (1.74 g, 12.6 mmol) and (DHQD) 2 PHAL (33 mg, 42.4 µmol, 1 mol-%) in tBuOH/H 2 O (1:1, 50 mL) at 0°C was added osmium tetraoxide (170 µL, 0.1  solution in toluene, 0.4 mol-%), followed by methanesulfonamide (0.4 g, 4.2 mmol). After stirring for 5 min at 0°C, the olefin 5 (1.13 g, 4.2 mmol) was added in one portion.…”

Quantum chemical study on asymmetric allylation of benzaldehyde in the presence of chiral allylboronate

“…In the asymmetric addition of aldehydes to allylboronates, modifying different chiral auxiliaries resulted in good to excellent enantioselectivity (Roush et al, 1985a;Jadhav et al, 1986;Brown et al, 1990;Racherla and Brown, 1991). And tartrate esters modified allylboronates from several laboratories have been studied thoroughly because of its simple preparation and high enantioselectivity (Haruta et al, 1982;Roush et al, 1985b;Roush et al, 1988;Roush et al, 1990a).…”