Rearrangements of Haloalkynol Derivatives of Glucofuranose

Abstract

Bromoalkynol derivatives of diacetone glucose undergo rearrangements to dihaloenol ethers contained in furo[3,4-b]furan cores when treated with halonium-producing reagents. [reaction: see text]

Facile Synthesis of 4‐(Trifluoromethyl)‐1 H‐isochromenes from Alkynols

“…[7,16] The Lewis acid [PdCl 2 (PPh 3 ) 2 ]a nd ZnCl 2 coordinates to thet riple bond and activates it to produce intermediate A,w hich is protonated to give enol ether intermediate B.T his intermediate reacts with the trifluoromethyl radicalg enerated in situ from Togni's reagent in the presence of CuI to form intermediate C.T his then undergoes single electron transfer (SET) [17] followed by deprotonation to generate the product 2a.…”

“…[4] Metal-catalyzed alkynol cyclization offers ar eliable and atom-economic methodo fo btaining highly functionalized, oxygen-containing heterocycles, [6] but this cyclization approachoften leads to protonation products withoutfurther derivatization. [7] Since incorporating atrifluoromethyl group into apotentially useful organic molecule can dramatically enhancei ts chemical and physicalp roperties, numerous efforts have been invested in developing facile and efficient syntheses of CF 3 -containing organic compounds. [8,9] Many electrophilic or nucleophilic trifluoromethyl reagents and trifluoromethanesulfinate salts act as efficient CF 3 sources.…”

Electrophilic halogenations of propargyl alcohols: paths to α-haloenones, β-haloenones and mixed β,β-dihaloenones

“…44,45,47,49 Instead, the haloalkynols of the two furanoses participated in a 5-exo-dig cyclisation or a haloetherication reaction (Schemes 45 and 46). 54,55 3-Haloethynyl-1,2-O-isopropylidene-5-O-methyla-D-pentofuranose 95a-b, converted from a series of reactions to the haloalkynol adduct from commercially available 1,2-O-isopropylidene-a-D-xylofuranose 94, was iodinated at room temperature with either NIS and catalytic TsOH combination or HTIB and iodine mixture in 5% water-solution and dry acetonitrile, respectively, to give a haloetherication product in high yields. Although both the haloetherication and the ring expansion (alkyl shi) are intramolecular, it appears that the intramolecular cyclisation of the primary methyl ether with the vinyl cation at the internal ethyne carbon, produced by alkyne iodination, is preferred over the C-4 alkyl shis of the 5membered ring (Scheme 45).…”

Synthesis of Heterocycles and Carbocycles by Electrophilic Cyclization of Alkynes

“…For example, an alkynyl acetal of diacetone glucose [34] Propargylic o-(1-alkynyl)phenyl ethers will rearrange in the presence of a Pd catalyst to afford mixtures of 3-allenyl-and 3-propargylbenzofurans (Equation 2.37) [37]. In a similar manner, analogous allylic ethers have been rearranged to 3-allylic benzofurans under similar conditions [26].…”