2.5- Dihydrofurans stereoselective synthesis

S. Arai, K. Nakayama, Y. Suzuki, K. Hatano, T. Shioiri, Stereoselective Synthesis of Dihydrofurans under Phase-Transfer-Catalyzed Conditions , Tetrahedron Lett. 

The stereoselective synthesis of c/.v-fused pyrano and furanobenzopyran can be achieved through the one-pot three-component reaction of o-hydroxy benzaldehyde, aromatic amines, and cyclic enolethers in the presence of catalytic amounts of Bi(OTf)3 (10 mol%) in air and the moisture-stable ionic liquid [bmim]PF6 [116]. The reaction of salicilaldehyde, aniline and 2,3-dihydrofuran furnishes the c/.v-fused furanochroman. In a similar fashion, various substituted salicilaldehydes and... 

Nacci, whose procedure involved the use of the ionic solvent n-butylpyridinium tetrafluoroborate, reported a stereoselective synthesis of 2,3-dihydrofurans <03JOC4406>. 

A stereoselective synthesis of 2,5-dihydrofurans has been accomplished by sequential SN2 cleavage of alkynyloxiranes (mainly anti SN 2 product) with Me2CuLi and silver(I)-catalyzed cyclization of the allenylcarbinol products <93JOC7180>. 

A novel and stereoselective synthesis of tmrw-2,5-disubstituted 2,5-dihydrofurans was reported recently <01T9335>. As can be seen below, a nucleophilic attack of phenyllithium... 

One of the more fascinating applications of the chelating effect is the stereoselective synthesis of 2-aryl-3-sullinyl-2,5-dihydrofurans (Scheme 14). The high stereocontrol is attributed to the Pd(ll) coordination with the dimethylamino group and the subsequent selective presentation of the tr-adduct during the insertion step (de = 70-88%). Consistent with this scenario, Heck arylations of non-amino-containing 4-arylsulfinyl-2,3-dihydrofurans resulted predominantly in the opposite diastereomers (de = 34-56%). 

In 2006, Gagosz and coworkers developed a stereoselective synthesis of functionalized dihydrofurans from butynediol monobenzoates (eqs 6 and 7) using 1 as catalyst. This reaction also employed an initial Au-catalyzed 3,3-rearrangement of propargylic carboxylates, followed by intramolecular stereos-... 

In 2006, Gagosz reported the gold-mediated stereoselective synthesis of 2,5-dihydrofurans from butynediol monobenzoates at room temperature. The transformation involved two sequential gold-catalysed reactions the formation of an allene derivative followed by a cyclisation. The reaction was... 

Scheme 16.60 Stereoselective synthesis of functionalised 2,5-dihydrofurans mediated by gold.

One of the more fascinating applications of the chelating effect is the stereoselective synthesis of 2-aryl-3-sullinyl-2,5-dihydrofurans (Scheme The high stereocontrol... 

An extensive study was undertaken to optimize the carbonyl-ene reaction between benzaldehyde (143, Scheme 30) and 3-methylene-2,3-dihydrofuran 144, which was utilized in the enantioselective synthesis of fluoxetine hydrochloride, a selective seratonin reuptake inhibitor.89 The degree of hydration of the molecular sieves proved important in the stereoselectivity of the reaction, with lower enantioselectivities reported both with highly active... 

Dihydrofuran reacts with /3,7-unsaturated a-keto esters with copper or zinc complex catalysts to generate furo[2,3-/ ]pyran derivatives in good yields with high stereoselectivity. The synthesis proceeds via an inverse electron demand hetero-Diels-Alder reaction <2000CC459>. 

Key step of Nicolaou s synthesis is the stereoselective hydrogenation of the unsaturated cyclo-dodecanone 17 which was obtained via intramolecular acetylide-aldehyde condensation of 6. The intermediate (Z)-olefm immediately rearranges to the tricyclic dihydrofuran 18 (Scheme 2). Solely the hydroxyl group at the quaternary carbon atom... 

An intermolecular Pauson-Khand reaction of a dihydrofuran intermediate was used to prepare a benz[ indenone, allowing for the first synthesis of a zirconocene benz[/]indene complex <03OL3153>. A stereoselective intermolecular Pauson-Khand reaction of 3-(R)-methyldihydrofuran was used to construct the desired diastereoisomer of oxabicyclo[3.3.0]octanone ring shown below in the total synthesis of the sesterterpene terpestacin <03JA11514>. 

The first total synthesis of the cytotoxic agent (+)-euplotin A was completed by the research team of R.L. Funk. The key step of the synthetic effort was the intramolecular hetero DIels-Alder cycloadditlon of a 3-acyl oxadiene (generated from 5-acyl-4H-1,3-dioxins via thermal retrocycloaddition) with a substituted dihydrofuran to afford the tricyclic skeleton of the natural product. The correct relative stereochemistry of the required dihydrofuran substrate was established using the Paterno-Buchi reaction between ethyl glyoxylate and furan. Subsequently, the oxetane ring was opened stereoselectively under Lewis acid catalysis. 

Scheme 11.64 Njardarson s synthesis of r+Vgoniothalesdiol utilizing a stereoselective Cu-catalyzed vinyl oxirane-dihydrofuran rearrangement.

Scheme 11.65 Njardarson s synthesis of labdane diterpenoids involving a stereoselective Cu-catalyzed vinyloxirane-dihydrofuran rearrangement.

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