Unusual regioselectivity in a Diels-Alder reaction of isoprene with levoglucosenone

Understanding reactivity and regioselectivity in Diels–Alder reactions of a sugar-derived dienophile bearing two competing EWGs. An experimental and computational study

“…This ease of pyramidalization of a CH over a fully substituted sp 2 carbon atom can be seen by measuring the out-of-plane bending angles  (also known as pyramidalization angles), 12 that were computed as described by Winkler and Dunitz to measure the distortion from planarity of amides.23 The average C3 and  C4 in TS-1+3and TS-1+4 are 19.9° and 32.2°, respectively, whereas in TS-2+3 and TS-2+4 the corresponding angles are higher ( C3 28.3º) and lower ( C4 29.5º), respectively, indicating that in 2 the difficulty of pyramidalization at C4 leads to an advanced out-ofplane distortion at C3. The same trend was also found in the case of isoprene(5), both in the para and meta modes of addition. As shown inFigure 1,TS-1+5-XP is slightly more asynchronous than TS-1+5-XM (d 0.23Å vs 0.18Å, respectively).…”

“…Analytical thin layer chromatography was carried out using commercial silica gel plates (Merck, Silica Gel 60 F254) and visualization was effected with short wavelength UV light (254 nm) and a panysaldehyde solution (2.5 mL of p-anysaldehyde + 2 5. mL of H 2 SO 4 + 0.25 mL of AcOH + 95 mL of EtOH) with subsequent heating.…”

Computational Chemistry to the Rescue: Modern Toolboxes for the Assignment of Complex Molecules by GIAO NMR Calculations

“…In 1996, Miftakhov et al. reported an unusual meta selectivity for the the Diels–Alder reaction between levoglucosenone ( 14 ) and isoprene, indicating 15 as the major isolated adduct, both under thermal and Lewis acid promoted conditions . More recently, from the basis of DFT calculations (conceptual DFT, transition state modeling, etc.…”

Reaction of levoglucosenone with Dane’s diene

“…The cycloaddition reaction was also carried out in the presence of such catalysts as ZnCl 2 [4], ZnBr 2 [17], EtAlCl 2 , TiCl 4 [21], BF 3 · Et 2 O [18,24], AlCl 3 -PhNO 2 in toluene [25,26], and 5 M LiClO 4 in Et 2 O [27]; the reactant ratio was 1 : 1, and methylene chloride or diethyl ether was used as solvent. The reaction of 1 with 2 in methylene chloride, catalyzed by ZnBr 2 , EtAlCl 2 , TiCl 4 , BF 3 · Et 2 O, or by AlCl 3 -PhNO 2 in toluene, afforded less than 1% of 3 and 4.…”

“…Cycloadditions of levoglucosenone (1) to 1,3-dienes provide a convenient synthetic route to optically active cyclohexene derivatives, and they follow general rules established for Diels-Alder reactions [1][2][3][4][5][6][7][8][9][10]. With the goal of elucidating the possibility of using levoglucosenone (1) as chiral inductor in the synthesis of steroids and obtaining an estrone analog containing a carbohydrate fragment instead of the D ring, in the present work we studied the reaction of levoglucosenone (1) with Dane's diene (7-methoxy-4-vinyl-1,2dihydronaphthalene).…”