Enolate Claisen rearrangement of esters from furanoid and pyranoid glycals

Synthesis of C‐1 Alkyl and Aryl Glycals from Pyranosyl or Furanosyl Chlorides by Treatment with Organolithium Reagents

“…The former was conveniently transformed into furanosyl chloride 22 upon treatment with PPh 3 and CCl 4 in THF at 60°C. [54] However, unlike previously reported by us, application of these reaction conditions to pyranose 21 caused isomerization previous to chlorination and resulted in the formation of 20. The formation of pyranosyl chloride 22 was carried out without isomerization under the conditions recommended by Hung and Wong [55] by treatment of 21 with nBuLi followed by ClPO(OPh) 2 in THF at -78°C.…”

Electrochemical fluorination of several esters derived from oxolane-2-yl-carboxylic acid, oxolane-2-yl-methanol and oxane-2-yl-methanol

“…Oxolane-2-yl-methyl trifluoroacetate (10) and oxane-2-yl-methyl trifluoroacetate (12) were prepared by the reaction of 2 and 3 with trifluoroacetic acid (Wako Chemicals Co.), respectively. The substrates synthesized for fluorination had the following boiling points: oxolane-2-yl-carbonyl chloride (6), bp 77-82 8C/30 mmHg (reported: bp 80-81 8C/30 mmHg [6]; bp 95-100 8C/33 mmHg [7]) methyl oxolane-2-yl-carboxylate (7), bp 87-92 8C/22 mmHg; oxolane-2-ylmethyl oxolane-2-yl-carboxylate (8), bp 130-132 8C/ 6 mmHg; oxolane-2-yl-methyl trifluoroacetate (10), bp Purity of anhydrous hydrogen fluoride (AHF) (Daikin Industries Co.) was more than 99.9%. The electrolytic fluorination apparatus and operating procedures were similar to those described previously [12].…”

“…It is known that oxolane-2-yl-carbonylchloride (6) is not stable on shelf standing at room temperature [6,7]. Actually, the evolution of large quantities of gases was observed when dissolved in AHF.…”

Synthesis of Pyranoid and Furanoid Glycals from Glycosyl Sulfoxides by Treatment with Organolithium Reagents

“…It has been suggested that heterolytic cleavage of the carbon-halogen bond occurs under these acidic conditions, initially to give an anomeric carbocation that, after taking two electrons from the zinc atom, generates a transient carbanion that evolves through the splitting off of an acetate anion. [10] Other reducing agents used in this transformation with glycosyl halides include sodium and potassium metal, [11] sodium naphthalide, [11] zinc/silver graphite, [12] aluminum amalgam, [13] SmI 2 , [14] potassium graphite, [15] lithium/ammonia, [16] chromium(II), [17,18] zinc/base, [19] cobalt(II), [20] and titanium(III). [21] A glucal derivative has also been prepared by introduction of a halogen atom at C-2, followed by a reductive elimination reaction in the opposite sense.…”