Studies of Diastereoselectivity in Diels−Alder Reactions of Enantiopure (SS)-2-(p-Tolylsulfinyl)-1,4-naphthoquinone and Chiral Racemic Acyclic Dienes

Abstract

Enantiopure sulfinylnaphthoquinone (+)-5 reacted with racemic acyclic dienes 1a-f bearing a stereogenic allylic center, through a tandem cycloaddition/pyrolytic sulfoxide elimination, to afford optically enriched compounds 8a-f and 9a-f with good like/unlike selectivities (ca. 75:25) and good enantiomeric excesses (68-82%), arising from the partial kinetic resolution of the racemic dienes. The opposite diastereoselection (8g-i: 9g-i, up to 5:95) was observed in reactions with dienes 1g-i, having an additional methyl group at C-3, the enantiomeric purities being moderate (14-25%). Steric effects and torsional interactions in the corresponding approaches account for the observed diastereoselectivities.

From Central to Helical Chirality: Synthesis of P and M Enantiomers of [5]Helicenequinones and Bisquinones from (SS)‐2‐(p‐Tolylsulfinyl)‐ 1,4‐benzoquinone

“…In accordance with previous conformational studies on 1,4‐dihydronaphthalenes37 and with our own work,38 tetrahydroaromatic derivative 19 would exist as a more stable boat‐like conformation such as I with the aryl substituent at C‐14c in a pseudoaxial disposition to avoid destabilizing interactions with the methylene group at C‐6a and the adjacent carbonyl group,37b,37c present in conformer II . However, a 1 H, 1 H NOESY experiment carried out on ( R )‐ 19 evidenced strong NOE enhancements between H‐14c and H‐5ax as well as with the methoxy group (R=Me) at C‐14.…”

P138: Hypervascular myoma in the right rudimentary horn in a patient with Rokitansky-Kuster-Hauser syndrome

“…In accordance with previous conformational studies on 1,4‐dihydronaphthalenes46 and with our own work,28c, 47 tetrahydroaromatic derivatives 16 a – c and 17 c , d would exist in a stable boat‐like conformation, such as I (Scheme ), in which the aryl substituent at C‐12b is situated in a pseudoaxial disposition to avoid destabilising interactions with the methylene group at C‐6a and the adjacent carbonyl group, present in the other possible conformer II . NOESY experiments carried out on 9,12‐dimethoxy‐substituted derivative 16 a confirmed the existence of a conformation such as I , as a NOE enhancement was observed between H‐8 ax and H‐12b, which is only possible if both hydrogen atoms are spatially close, such as in conformer I .…”

Organocatalyzed benzannulation for the construction of diverse anthraquinones and tetracenediones

“…The structures of the regioisomers, 3q to 3q 0 or 3r and 3r 0 , were confirmed by a comparison with the data of the authentic compounds. 16,17 The signals of one aromatic proton at C-5 for compounds 3q and 3r showed upfield shifts (3q: 7.97 ppm and 3r: 7.86 ppm) with respect to those of compounds 3q 0 and 3r 0 (3q 0 : 7.98 ppm and 3r 0 : 7.90 ppm). On the other hand, the reaction of 1b with (E)-2-methyl-2-butenal (2f) provided products 3q and 3q 0 in 66% yield with a 15 : 85 ratio of regioisomers, whereas the treatment of 1c with 2f afforded 3r and 3r 0 in 77% yield with the reverse isomer ratio of 74 : 26.…”

“…Reactions with only 10 mol% benzoic acid in the absence of L-proline (entry 13) or at room temperature (entry 14) gave no products. With different solvents, such as CH 2 Cl 2 , CH 3 CN, THF, PhF, benzene, and DMF, the desired product 3a was obtained in lower yield (entries [15][16][17][18][19][20]. The structure of compound 3a was determined by a comparison with the spectral data of the reported compound.…”