Furan ring tetrahydro

Finally, two termination steps are considered a spontaneous termination with acid expulsion and restoration of a terminal 2,3-dihydro- or furan ring and a recombination of the growing ion pair to give a tetrahydro- or a 2,3-dihydrofuran ester. 

Isosorbide is a rigid diol with two non-equivalent hydroxyl groups (endo-5 and exo-2) and two tetrahydro-furan rings in its structure ... 

Some methods dealing with chain extensions are reviewed in this section. Additional methods dealing with extensions at Cl are then detailed. Selected methods designed for the formation of C-glycosidic bonds, that is, for the formation of tetrahydro-pyrans or furan rings, are described in Section 11.5. 

The hydrolysis (or alcoholysis) of furans involves nucleophilic addition of water (or an alcohol) to an initially formed cation, giving rise to open-chain 1,4-dicarbonyl-compounds or derivatives thereof. This is in effect the reverse of one of the general methods for the construction of furan rings (18.13.1.1). Suc-cindialdehyde cannot be obtained from furan itself, presumably because this dialdehyde is too reactive under conditions for hydrolysis, but some alkyl-furans can be converted into 1,4-dicarbonyl products quite efficiently, and this can be viewed as a good method for their synthesis, and of cyclopentenones derived from them. ° Other routes from furans to 1,4-dicarbonyl compounds are the hydrolysis of 2,5-dialkoxy-tetrahydro-furans (18.1.1.4) and by various oxidative procedures (18.2). 

Furan and its methylated homologues undergo cationic polymerization initiated by both Lewis and Brpnsted acids, but the fact that the ensuing branched products (DP = 50-300) bear complex and irreproducible structures, made up of both dihydro- and tetrahydro-furan rings [4a, 4d], casts serious doubts about their interest as materials. Claims related to the synthesis of regular macromolecular structures with these monomers were not substantiated by convincing spectroscopic evidence. 

The structure of nonactin was elucidated by Gerlach and coworkers, who found that nonactin was a macrocyclic ester consisting of four alternating units of levorotatory and dextrorotatory nonactic acid, a hydroxy acid containing a cis-tetrahydro-furan ring. In 1975, the structure of nonactin was confirmed by total syntheses by Gerlach and by Schmidt. ... 

The 17a-ethynyl compound (59) has been prepared in 88% yield from estr-4-ene-3,17-dione (58) and acetylene, at 2-3 atm pressure in tetrahydro-furan in the presence of potassium t-butoxide. Presumably the A-ring enone system is protected as the enolate anion during the course of the reaction. 

Iodination of 4 with molecular iodine in the presence of mercuric oxide formed the 3-iodo derivative (52JA4951 66CJC2283). Iodine in tetrahydro-furan oxidatively cyclized /3-(3-benzo[b]thienyl)-a-mercaptoacrylic acids rather than iodinating the thiophene ring [70JCS(C)2431]. 

Anew route to 2,5-dihydrofiirans and tetrahydro[3,2-b]furans via ring contraction of pyranoside C-glycosides was reported <96CC1663>. ( )-Homononactic acid and its 8-epimer were synthesized by using a c -selective iodoetherification as the key step (Scheme 21, <96SL777>). 

El3unoclavin und Lysergol durch Reduktion mit LiAlHj in Tetrahydro-furan bewiesen werden. Somit war gesichert, daB in der neuen Saure die Ringe C und D trans verkniipft sind und daB sie am Cg und 0 die gleiche absolute Konfiguration wie Dihydro-lysergsaure besitzen muB. 

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