Regioselective syntheses of substituted furans

Silanes have proven extremely useful for the synthesis of multi-substituted furan rings. Their judicious placement on a furan ring can be used to control either the placement of new groups around the furan ring or the silane can be directly replaced via an ipso-substitution. This paper will briefly review the role silicon has played in the preparation of furan rings having a variety of substituent patterns.

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Synthesis of multi-substituted furan rings: the role of silicon

The first total asymmetric synthesis of (+)-xestoquinone (1) has been accomplished in 68% ee by a palladium(0)-catalyzed polyene cyclization of naphthyl triflate 44 using (S)-(+)-BINAP as the chiral ligand. Attempts at an asymmetric polyene cyclization using the corresponding naphthyl bromide 41 gave poor enantioselectivities even in the presence of silver salts, thus exemplifying the effect of the coordination state of palladium on the enantioselectivity. A new method for the preparation of 6,7-dihydroisobenzofurans is also described using a [1,2]-Wittig rearrangement on a seven-membered cyclic ether precursor.

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Total synthesis of (+)-xestoquinone using an asymmetric palladium-catalyzed polyene cyclization

A new stereoselective synthesis of (Z)-vinylsilane allylic alcohols

A palladium catalyzed cross-coupling between furylborates (generated in situ) and organohalides

The 1,4 O→C silyl migrations of various 3-[(trialkylsilyl)-oxymethyl]-furans and -thiophenes

The regiospecific formation and reactions of 4-lithio-2-(t-butyldimethylsilyl)- 3-(hydroxymethyl)furan: An approach to 3,4-disubstituted furans.

Numerous 3-[(trialkylsilyl)oxymethyl]-furans and -thiophenes undergo a 1,4 O→C silyl migration when treated with n-BuLi/HMPA in THF or DME to produce 2-(trialkylsilyl)-3-(hydroxymethyl)-furans and -thiophenes in good yields.

Edward J. Bures

Papers

The 1,4 O→C silyl migrations of various 3-[(trialkylsilyl)-oxymethyl]-furans and -thiophenes

The regiospecific formation and reactions of 4-lithio-2-(t-butyldimethylsilyl)- 3-(hydroxymethyl)furan: An approach to 3,4-disubstituted furans.

The 1,4 O→C Silyl Migrations of Various 3-((Trialkylsilyl)oxymethyl)furans and -thiophenes.