Nucleophilic displacement of methide from silicon. Steric compression of geminal trimethylsilyl groups?

An unexpected cyclization reaction of tert-butyl o-trimethylsilylphenyl sulfoximine

“…Comparable cyclization reactions have been reported for the action of iodine on a β-trimethylsilyl substituted acrylate 8 and as result of an intramolecular alkoxide attack also invoking hypervalent silicon intermediates. 9,10 For highly acidic o-trimethylsilyl α-trifluoromethyl benzyl alcohols the cyclization occurs spontaneously in polar aprotic solvents with extrusion of hydrocarbons. 11 However, this type of reaction was not observed when the title compound 5 was heated in DMSO or acetonitrile.…”

Regiospecific synthesis of 1-silyl substituted 1,4-dienes

“…The sterically fixed six-membered representatives (3d) and (3f) give a slow conversion (5-7 h, 7OoC), whereas (3a) and (3c) are eliminated smoothly (2 h, 50°C) (Table 2). Interestingly, (7) or (8) could not be detected under these conditions (Scheme 3).…”

A “Spacer”‐Modified Trisaccharide as Photolabile Ligand for Affinity Labeling of Antigalactan IgA X24

“…galactopyranosyl-[-l,2 : 3,4-d1-O-isopropylidene-8-azi-]-~-golacto-undeca-1.5pyranose (6) [13]: 2 (0.3 g, 0.84 mmol) was coupled with 3 (680 mg, 9.2 mmol) in the presence of 7 g of silver silicate-alumina catalyst according to a Koenlgs-Knorr synthesis modified by H . Paulsen…”

“…The high affinity of compound 1 (1.1 x lo5 M-'), exceeding by far that of the structurally comparable disaccharide (Table I), indicates an optimal, stable occupation of the four- gel with ethyl acetate/cyclohexane, 1:l; R, = 0.16. After evaporation of the corresponding fractions, 5 [13] was obtained as a colorless, solid foam (10.7 g, 94%; [a]; ' -5" (chloroform)). Bromination of 5 was carrled out by modification of a known procedure [lo] at lower temperature (-5 "C) in the presence of acetic anhydride: 5 (0.2 g, 0.294 mmol) was dissolved in 15 mL of a 2: 1 mixture of acetic anhydride and 30% HBr in acetic acid at 0 "C and the resulting mixture was cooled to -5 "C. After 48 h, the starting material had undergone complete reaction [lo].…”