391929-00-3Relevant academic research and scientific papers
Synthesis of optically active 2-alkoxy-2H-pyran-3(6H)-ones. Their use as dienophiles in Diels-Alder cycloadditions
Iriarte Capaccio,Varela
, p. 8859 - 8866 (2001)
Optically active 2-alkoxy-2H-pyran-3(6H)-ones (4a-d) were synthesized in one step by the tin(IV) chloride-promoted glycosylation and rearrangement of the 2-acetoxy-3,4-di-O-acetyl-D-xylal (3) prepared from D-xylose (1). The absolute configuration of the new stereocenter at C-2 was determined by chemical transformation of the dihydropyranones 4a and 4b into the known alkyl pentopyranosides (7a and 7b, respectively). Also, from 1H NMR experiments using a chiral ytterbium shift reagent, the enantiomeric excesses for 4a (> 86%) and 4b (>77%) were established. Enantiomerically pure 4c and 4d were obtained by reaction of 3 with chiral 2-octanol (R and S, respectively). Dihydropyranones 4a-d were employed as dienophiles in Diels-Alder cycloadditions with 2,3-dimethylbutadiene and butadiene. Under thermal conditions, only moderate yields (～50%) of cycloadducts 9a-c and 10a were respectively obtained with good diastereofacial selectivity (> 80%). Optimized Lewis acid promoted cycloadditions led to 9a-d and 10a,c in higher yields (～80%) and with higher diastereoselectivities (> 94%). The major products were formed by approach of the dienes from the less hindered face of the dihydropyranones, and the minor products (such as 11a) were formed by addition from the opposite side. Furthermore, cycloadduct 9a was stable in an alkaline solution, whereas 11a underwent epimerization under the same conditions.
Reactions of Diels-Alder adducts of a sugar-derived dihydropyranone leading to fused polycyclic compounds
Capaccio, Christian A. Iriarte,Varela, Oscar
, p. 1207 - 1213 (2007/10/03)
Manipulation of the ketone and alkene functions of cycloadducts 2, 3, and 4, derived from optically active (ee >86%) (S)-2-benzyl-2H-pyran-3(6H)-one (1), led to polycyclic systems having three or four fused rings. Reduction of the carbonyl group of the butadiene adduct (2) took place with low facial selectivity affording the alcohols 5 and 6 in 1:1.4 ratio. In contrast, a higher diastereoselection was observed for the reduction of the carbonyl of the cyclopentadiene adducts 3 and 4 to give the endo alcohols 10 and 13, respectively. The epoxidation of 6 showed low facial selectivity in the formation 7 and 8, whereas epoxidation of 10 and 13 took place from the exo face of the norbornene system to give spontaneously the polycyclic alcohols 11 and 14 by opening of the epoxide by intramolecular attack of the hydroxyl group of the pyranoid ring. Similarly, addition of iodine to 10 led to the polycyclic iodide 12.
