Dihydrofurans synthesis

Allenyl alcohols have been used as starting materials for a different kind of dihydrofuran synthesis. This is a process with great generality and utility in total synthesis. An example of the process is shown in Eq. 13.43 [42]. Treatment of allenyl alcohol 133 with silver nitrate in aqueous acetone at room temperature leads stereospe-cifically to dihydrofuran 134 in excellent yield. A similar reaction occurs with allenyl ketones, leading to furans. The isomerization is known to take place with Rh(I) [43], Ag(I) [44, 45] Pd(II) [46], Au(III) [47, 48] Cu(I) [49] or Hg(II) [50, 51],... 

Certain acyclic diazoketones react with electron-rich alkenes (such as enol ethers) to form dihydrofurans. The catalyst of choice is Rh2(OAc)4 for these and related transformations, although copper catalysts have been used as well. A variety of ot-diazoketones and ot-diazoaldehydes can be used, including PhCOCHN2, NjCHCOCOOEt, MeCOC(N2)COMe, and MeCOC(N2)COOR (345,346). Wenkert (347) and Alonso (348) studied the scope of this dihydrofuran synthesis [Scheme 8.75 e.g., 304 305 R = H (349), COOEt (350)]. 

To extend this powerful new dihydrofuran synthesis to more complex systems, related reactions with branched /1-dicarbonyl systems were investigated [20]. hi a similar fashion, the cfs-fused furanoids 40 and 41 were prepared from hexane-2,4-dione (37), ethyl isobutyryl acetate (38), and 2. These targets are important chiral synthons, since there are many natural products bearing ethyl and isopropyl residues on furanoid rings. The flexibility of this method was also tested with the aromatic /3-diketone 39 yielding furanoid 42, which is an important system for tetralone synthesis (Scheme 8). 

Kilroy, T.G., Cozzi, P.G., End, N. and Guiry, P.J. (2004) The application of HETPHOX ligands to the asymmetric intermolecuiar Heck reaction of 2,3-dihydrofuran and 2,2-disubstituted-2,3-dihydrofurans. Synthesis, 1879-88. 

Furan and Dihydrofuran Synthesis. Trapping the 3-lithio derivative of (1) with decanal leads to the allenic alcohol (eq 2). Aqueous acid under carefully controlled conditions produces 2-trimethylsilyl-5-nonylfuran. The addition product of the 3-lithio... 

Adam, W, Griesbeck, A.G., GoUnick, K., and Knutzen-Mies, K., 1,2-Dioxetanes derived from 4,5-dimethyl-2,3-dihydrofuran synthesis via photooxygenation, activation parameters and excitation properties, /. Org. Chem., 53,1492, 1988. 

Palladium-carbon Carboxylic acid esters from 2,3-dialkoxy-2,3-dihydrofurans Synthesis with addition of 3 C-atoms... 

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