Tetraarylcyclopentadienones 2a-c react with (E)-3,4,5,6,7-penta-0-acetyl-l,2-dideoxy-1-C-nitro-D-galacto-(la) and -Dmanno-hept-I-enitol (lb) to give l-C-(2,3,4,5-tetraaryIphenyl)-D-gakKtO-(3a-c) and -D-manno-penta-0-acetylpentitol (3d-f), respectively, after decarbonylation and HN02 e&-nation from the Diels-Alder cycloaddition intermediates.The interest in the synthesis of aryl C-glycosides [l] has increased in recent years because a few natural products possessing this kind of structure have been found to display potent antitumor activityL21. Most of the synthetic routes to aryl C-glycosides are based on the formation of a C-C bond between a suitable aromatic compound and the anomeric carbon atom of a sugarC3]. We have selected the approach to the formation of the aryl moiety by using cycloaddition of a suitable sugar derivative to an appropriate diene. In fact, carbohydrate derivatives act as dienophiles in Diels-Alder reactionsL4-61. In this way, norbornene-Fsl or cyclohexenealditols~61 have been obtained by uncatalyzed Diels-Alder cycloaddition of l-nitroalkenyl sugars to cyclopentadiene or butadienes, respectively. Since the nitro group in sugar derivatives sometimes acts as a leaving group by HN02 elimination[l, I-nitroalkenyl sugars are suitable candidates for cycloaddition reactions leading to aryl C-glycosides. On the other hand, cyclopentadienones[81 are efficient dienes in Diels-Alder cycloadditions, but their reactions with sugar derivatives are not known. In this paper we report on the cycloadditions of (E)-3,4,5,6,7-penta-0-acetyl-1,2-dideoxy-1 -C-nitro-~-guluctohept-1 -enitol (1 a) and Q-3,4,5,6,7-penta-O-acetyI-1,2-dideoxy-1 -C-nitro-D-rnunno-hept-1-enitol (lb) to 3,4-diaryl-2,5-diphenylcyclopentadienones (2a-c) which afford new l-C-(3,4-diaryl-2,5-diphenylpheny1)alditols (3a-f).Thus, when l a was treated with tetracyclone (Za) an amorphous solid was obtained as the sole reaction product. The 'H-and I3C-NMR spectra of the product only showed signals corresponding to the sugar chain and the aromatic moiety. Thus the arylalditol structure 3a was assigned to the above product which was obtained in 47% yield. The IR, mass spectral, and analytical data confirmed, besides the loss of CO, the elimination of HN02 from the initial Diels-Alder adduct. When 3,4-bis(p-methoxyphenyl)-(2b) or 3,4-bis(p-bromophenyl)-2,5-diphenylcyclopentadienone (2c) were used instead of tetracyclone (Za), the reactions with l a furnished much lower yields (26% for 3b and 19% for 3c). In each case a unique product was obtained. Reaction products for l a are shown in Scheme 1. Similarly, when compound l b was allowed to react with tetracyclone 2a, the arylalditol3d was obtained in 59% yield which was the highest yield in these reactions. As in the case of la, only the product arising from decarbonylation and elimination of HN02 from the initial Diels-Alder adduct was obtained. Unfortunately, when 2a was treated with substituted cyclones 2b and 2c, the yields of the corresponding products were very low (8% for 3e and 20% Evidence...
