Loganin aglycone

Sultam-modified acrylates undergo [4 + 2]-cy-cloadditions with 1,3-dienes with excellent endo- and side-selectivity in the presence of EtAlCl2 or TiCl4 [7-9]. This feature could be used for an effective synthesis of the loganin-aglycon 9 (Scheme 2) [10] ... 

Activattd dimethyl sulfoxide oxidations have been fairly well used in the synthesis of monoterpenes, as seen in the oxidation to an aldehyde of the alcohols (40), en route to loganin aglycone, and (41), a precursor in a synthesis of specionin (equation 16). ... 

Tietze etal. have described efforts to convert 7-0-acetyl-loganin aglycone into loganin and the corresponding a-glucoside by standard glucosylation proce-dures. ... 

Figure 6.15. Natural products synthesized using asymmetric cycloadditions to chiral dienophiles as the key stereodifferentiating step sarkomycin [167,195] brefeldin A [168] (of the 3 stereocenters formed in the asymmetric acrylate/cyclopentadiene cycloaddition, the indicated stereocenter is the only one retained) 0-methyl loganin aglycone [196] bilabolide [197] yohimbine [198].

The first two syntheses of loganin aglycone 58 have been performed in a similar manners by Buchi, Tietze et al. ( see scheme 10-13, ref 23 ) and by Partridge et ai. 

This olefin undergoes photoannelation in regioselective and stereoselective manner with methyl-diformyl acetate 48 to produce directly the loganin aglycone derivative 58 in about 20% yield. Classical treatment with 2,3,4,6-tetra-O-acetyl-D-glucose in anhydrous conditions, in the presence of boron trifluoride etherate, afforded loganin pentaacetate 59. 

Alkylsilanes react with acid chlorides under catalysis with AICI3 to give unsym-metrical ketones.Compound (45) is obtained by reaction of 5-tri-methylsilylcyclopentadiene with dichloroacetyl chloride in the presence of tri-ethylamine, and it may be converted into prostaglandins or into loganin aglycone acetate (46), by subsequent modifications. Compounds (47) and (48) are obtained from photochemical cycloadditions of alkynylsilanes, RC=CSiMe3, with cyclopent-2-enone. ... 

The appreciable synthetic potential of the de Mayo reaction has been applied to the preparation of polycyclic natural products. Some recent developments are shown in Table 4. The de Mayo reaction was used as the key step in the synthesis of hirsutene (entry 1), fusicoccin H aglycone (entry 2), taxanes (entries 3 and 4), loganin (entries 8 and 9), sarracenin (entry 10) and iridoid intermediates (entry 11). 

The classical glucosylation with 2,3,4,6-tetraacetylglucose, afforded the acetate of loganin 59, via the aglycone 58. 

Oppolzer et al. developed useful auxiliaries based on a camphor precursor,231 and one of the best was a sultam (277). When this sultam was converted to an acrylamide (278) and reacted with butadiene, cycloadduct 280 was produced (85% yield, 95 % ee).232 Selectivity in this Diels-Alder reaction is due to chelation of the amide oxygen and the sulfonyl group, as shown in 279. Oppolzer and co-workers applied this methodology to a chiral synthesis of the aglycone of loganin.233... 

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