Stereocontrolled Preparation of Spirocyclic Ethers by Intramolecular Trapping of Oxonium Ions with Allylsilanes

Vicinal Tetrahydrofuranyl Substitution of Alkyl Chains. Tetra-, Penta-, and Hexafunctionalized Arrays

“…Metal alkoxides have previously been recognized to be effective promoters of the conversion of aldehydes into esters, [23][24][25] with effective reduction of one carbonyl and oxidation of the other. In the present instance, it is conceivable that effective chelation of the metal center in the Grignard reagent to multiple tetrahydrofuranyl oxygens 26 acts to curtail the rate of 1,2addition. With the adventitious buildup of magnesium alkoxides and hydroxides comes the opportunity for Cannizzaro-type chemistry, 27 since neither aldehyde is enolizable.…”

Stereoselective Synthesis of C‐ and N‐Ketosides by Lewis Acid‐Catalyzed C‐ and N‐Glycosidation of Alkynyl, Phenyl, and Methyl Ketoses

“…C 81.30, H 6.67; found C 80.98, H 6.44. 5, 73.0, 73.5, 74.6, 75.0, 75.5, 76.1, 78.0, 82.8, 84.9, 86.6, 89.7, 121.9, 127.4, 127.5, 127.6, 127.7, 127.8, 127.9, 128.0, 128.1, 128.1, 128.2, 128.3, 128.4, 128.5, 129.0, 131.6, 132.8, 138.1, 138.2, 138.5, 197.0 6,6.0 Hz,1 H),4.24 (d,J ϭ 11.4 Hz,1 H),4.43 (d,J ϭ 12.2 Hz,1 H),4.50 (d,J ϭ 11.4 Hz,1 H),4.72 (d,J ϭ 12.0 Hz,1 H),4.80 (d,J ϭ 11.4 Hz,1 H),4.86 (d,J ϭ 6.0 Hz,1 H),4.97 (d,J ϭ 11.4 Hz, 1 H), 6.07 (s, 2 H), 6.12 (s, 2 H), 6.97Ϫ7.47 (m, 25 H) ppm. 13 C NMR (75 MHz, CDCl 3 ): δ ϭ 55.…”

“…[3] Additionally, several C-glycosides are potent antitumor, antiviral, or antibiotic agents. [4] On the other hand, C-ketosides [5] or bis-C,C-glycosides [6] (2) have not found similar favor, [7] although methods for the preparation of spirocyclic bis-C,C-glycosides [6,8,9] and C-glycosides of ulosonic acids [10,11] have been reported by several groups. One of the more extended methods for the stereoselective synthesis of C-glycosides is based in the pioneering work of Kishi and collaborators, [3] and is outlined in Scheme 2.…”

Cascade Rearrangements Following Twofold Addition of Alkenyl Anions to Squarate Esters

“…Previously, halogen atoms and oxygenated substituents were shown to be notably effective in this role. thioallylamine to squarate esters has also been systemati- Scheme 15 For amino groups, the extent of elimination has been found 110a and 110b [43] . Competitive conrotation within either of these diastereomeric coiled conformations will be subject to to be dependent on the structural features of the companion nucleophile [42] .…”