Tetrahydro furan synthesis

Shat general strategies can you suggest for the synthesis of Symmetrical 2,3-di substituted tetrahydro-furans (48) ... 

Some A -enecarboxylic acids undergo a rapid intramolecular cyclization reaction of the 5-exo-trig type prior to the radical coupling step. Substituted tetrahydro-furans [95] and pyrrolidines [96] can be prepared by this Kolbe route. It is preferable to protect the amine function in the pyrrolidine synthesis by N-formy ation in... 

The synthesis of 168 has also been completed by using other reaction conditions (Scheme 22). 6,7-Dimethoxyisoquinoline (162) was reacted with potassium cyanide and 2-chloromethylbenzoyl chloride in the presence of a catalytic amount of benzyltriethylammonium chloride, resulting in 164 which on treatment with lithium diisopropylamide in hexamethylphosphoramide-tetrahydro-furan solvent mixture afforded the cyclized product 168 in high yield (40). 

The complex forms purple air-stable crystals and has good solubility in both polar and nonpolar solvents (e.g., acetone, dichloromethane, tetrahydro-furan, benzene, and hexane). It has been characterized crystallographically.7 The structure is an open, but folded, ladder-like array of six metal atoms with the two platinum atoms in the center. The IR spectrum (hexane) exhibits V(co> bands at 2085 (m), 2062 (vs), 2035 (vs), 2016 (w). Pt2Ru4(CO)18 has been found to be very useful for the synthesis of new platinum-ruthenium cluster complexes.10,12,13... 

Several recent reviews have included specific types of electrophilic cyclofunctionalization reactions.1 Important areas covered in these reviews are halolactonization u cyclofunctionalization of unsaturated hydroxy compounds to form tetrahydrofurans and tetrahydropyrans lb cyclofunctionalization of unsaturated amino compounds lc cyclofunctionalization of unsaturated sulfur and phosphorus compounds ld lf electrophilic heterocyclization of unconjugated dienes 1 synthesis of y-butyrolactones 1 h synthesis of functionalized dihydro- and tetrahydro-furans lj cyclofunctionalization using selenium reagents lk lm stereocontrol in synthesis of acyclic systems 1" stereoselectivity in cyclofunctionalizations lP and cyclofunctionalizations in the synthesis of a-methylenelactones.lq Previous reference works have also addressed this topic.2... 

Z. Sun and R. S. Hosmane, Fulgides and photochromism. Synthesis of (E)-and (Z)-5-dicyano-methylene-4-dicyclopropylmethylene-3-[l -(2,5-dimethyl-3-furyl)ethylidene] tetrahydro-furan-2-one, Tetrahedron Lett., 36, 3453-3456 (1995). 

Recently, Potts and Liljegren (97) have synthesized J15> 20-yohimbene (XXXV) by condensation of 3-chloroacetylindole with 5,6,7,8-tetra-hydroisoquinoline, and reduction of the tetracyclic quaternary chloride (XXXIV) so obtained with lithium aluminum hydride in tetrahydro-furan (THF) solution. Since A15> 20-yohimbene (XXXV) has previously been converted by palladium-maleic acid dehydrogenation into 5,6-dihydrosempervirine (XXXIII) (98) and sempervirine (99), this constitutes a third formal synthesis of sempervirine. 

The key step in a short synthesis of ( )-tylophorine77 is an intramolecular double conjugate addition reaction. Reaction of the ( , )-unsaturatcd ester 1 (R2 = 8-phcnylmcnthyl) with ferf-butyldimethylsilyl triflate in the presence of excess of triethylamine in dichloromethane produces an 80 20 inseparable mixture of the indolizidines 2A and 2B78. Treatment of a mixture of 2A and 2B (R2 = 8-phenylmethyl) with sodium hydride in refluxing tetrahydro-furan for 2.5 hours gives the single indolizidine 2 A. Dioxanyl ester 1 furnishes, on reaction with... 

Part A illustrates a general method of preparing a,0-unsaturated j8-keto amines (/3-keto imines cf. synthesis 13), a class of weakly acidic bidentate ligands. Part C illustrates the use of chromium(III) chloride-tris(tetrahydro-furan) in the synthesis of a chromium(III) complex under nonaqueous conditions. 

Cyclkation. Generation of oxonium ions and their intramolecular trapping are conveniently performed in the presence of DBU in the context of a tetrahydro-furan/tetrahydropyran synthesis. O-Mesyloximes possessing an active methine undergo cyclization, and this reaction leads to dihydropyrroles and tetrahydropyridines. 

Oxidation. As one step in the synthesis of furaneol (3, a flavor principle of pineapples and strawberries), Biichi et al. wished to effect hydroxylation of 2,5-dimethyl-2,5-dimethoxy-2,5-dihydrofurane (1). They tried oxidation of (1 15.8 mmole) with potassium chlorate (22.8 mmole) and osmium tetroxide (0.3 mmole) in aqueous tetrahydro-furane containing sodium bicarbonate at 30 for 63 hr.2 however, the expected diol... 

The cleavage of a terminal )3-phenylsulfonyl silyl group to give a methylenecyclopropane is readily accomplished by treatment with tetrabutylammonium fluoride (TBAF) in tetrahydro-furan. Thus, the bis(benzyl) ether of trani-3-methylenecyclopropane-l,2-dimethanol, trans-, 2-bis[(benzyloxy)methyl]-3-methylenecyclopropane (2), was obtained in 91% yield as part of a synthesis of oxetanocin. ... 

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). 

Addition to ketones under similar conditions shows an improved diastereofacial selectivity, with the following examples delivering only a single stereoisomer. The efficiency and control available in these transformations results in a very useful synthesis of a variety of tetrahydro-furans in a stereocontrolled fashion30. 

Dicarbonyldihydridobis(triphenylphosphine)osmium(II) was first prepared by allowing OsH2(CO)4 to react with three equivalents of triphenylphosphine in tetrahydrofuran at reflux temperature for 12 hours.9 It has also been prepared by treatment of Os(CO)3-[P(C6H5)3]2 with hydrogen at 120 atmospheres pressure and 130° in tetrahydrofuran for 12 hours.9 The yield was 50 %, and the product was purified by fractional crystallization from n-heptane-tetrahydro-furan. The procedure described below2 is a rapid, single-stage synthesis. 

Synthesis of monodisperse PHOST was first reported by Nakahama et al. [145], who demonstrated that 4-terf-butyl(dimethyl)silyloxystyrene undergoes living anionic polymerization with butyllithium as the initiator in tetrahydro-furan (THF) at cryogenic temperatures under high vacuum and that desilyla-tion of the resulting polymer with HC1 cleanly yields monodisperse PHOST. It... 

In view of the extremely laborious method employed by Willstatter to obtain cyclooctatetraene, it is noteworthy that a very simple synthesis has been discovered by Reppe (239). A solution of acetylene in tetrahydro-furan is heated to a pressure of 20 atmospheres in the presence of a cat-... 

The most studied are the methods for the synthesis of perfluorinated tetrahydro-furan derivatives. 

---