Factors in the formation of isomerically and optically pure alkyl halides. Part XI. Vilsmeier reagents for the replacement of a hydroxy-group by chlorine or bromine

Synthesis of tri- and tetrasaccharide haptens related to the Asialo forms of the gangliosides GM2 and GM1

“…The chromatographic separation of 10 from the 1-nitrates (8 and 9) complicates the preparation of the bromide 11. It is now found that the treatment of the crude reaction mixture with Vilsmeier reagent (N, N-dimethy lbromoforminium bromide (27)) rapidly converts 10 to 11. This reaction is followed by the addition of the lithium bromide to convert the nitrates 8 and 9 into the desired bromide 11 which was isolated as a syrup by column chromatography in 40% overall yield.…”

“…Drorr1ide (18) Vilsmeier bromide (27) (1.31 g, 6.05 mmol) was added to an ice-cold solution of compound 17 (1.88 g, 4.32 mmol) in dichloromcthanc (25 mL) and stirred. sjw-Collidine (0.802 mL, 6.05 mmol) was added dropwise to the rcaction mixture.…”

“…Evaporation of the first and main fraction left a solid (2.7 g, 62% yield) which appeared homogeneous on tlc. ' The analytical sample was prepared by crystallization from (27) (720 mg, 3.31 mmol) was added to a solution (0°C) of compound 29 (1.2 g, 1.65 mmol) in dichloromcthane (1 5 mL). g~rn-Collidine (440 pL, 3.63 mmol) was addcd dropwise and thc mixture was stirred at O°C for 6 h and thcn at room tcrnperature for 18 h. After washing with ice-cold water, dilutc hydrochloric acid, saturated aqueous sodium bicarbonate, and finally with watcr.…”

Novel Synthetic Method for the Vilsmeier-Haack Reagent and Green Routes to Acid Chlorides, Alkyl Formates, and Alkyl Chlorides

“…We have recently reported a new method for the preparation of the Vilsmeier-Haack reagent (VH) [1][2][3][4][5][6]. Our method obviates the use of toxic reagents such as phosgene, thionyl chloride, or phosphoryl chloride, which are used in the conventional method.…”

Syntheses of derivatives of lacto-N-biose. I. 4,6-Di-O-acetyl-3-O-(tetra-O-acetyl-β-D-galactopyranosyl)-2-deoxy-2-phthalimido-α,β-D-glucopyranosyl chloride

“…We conduct the reaction in the presence of sym-collidine to neutralize the liberated hydrogen chloride. Since the Vilsmeier reagent is also available in the bromide form (29,30), the more reactive glycosyl bromides are also available in this way. We would also like to note that the reaction can be applied to such acid-labile compounds as 2,3,4,6-di-0-isopropylidene-D-mann o p y r a n o~e .~ In the phthalimido method, under the conditions for glycosylation which utilize an equimolar mixture of silver triflate and sym-collidine as promotor (6), the more stable chlorides are adequately reactive.…”