Stereoselective Synthesis of 3-Oxygenated-<i>cis</i>-dialkyl-2,5-substituted Tetrahydrofurans from Cyclohexadienediols
作者:Margarita Brovetto、Gustavo Seoane
DOI:10.1021/jo800514k
日期:2008.8.1
The 3-oxygenated-cis-dialkyl-2,5-substituted tetrahydrofuran system, present in several natural products, was prepared with good selectivity by acidic cyclization of 5-alkene-1,2,4-triol derivatives. The starting alkenol was obtained in few steps from a chiral cis-diol resulting from microbial oxidation of bromobenzene. The study of the cyclization allowed the rationalization of all experimental results by assuming a complete ionization at the allylic position and a model close to the one proposed by Labelle for homoallylic induction in five-membered ring closures.
Acyloxyalkylidènephosphoranes—I
作者:A. Hercouet、M. le Corre
DOI:10.1016/s0040-4020(01)92355-5
日期:1981.1
The ω-acyloxy n-propylidenephosphoranes give 2,3-dihydrofurans in toluene, and cyclopropylcetones in t-butanol. The mechanism of these reactions was investigated; formation of cyclopropylketone does not result from intramolecular condensation but from two intermolecular condensations.
The PdII-catalyzed tandem cyclization of chiral allylic alcohols possessing an internal epoxide and a terminal alcohol provided a contiguous THF–THP and THF–THP ring units stereospecifically. The cyclizations take place via a 5-exo-tet-5-exo-trig mode, however, the cyclization of methyl substituted epoxy diols proceeded via 6-endo-tet-6-exo-trig fashion in a part to construct the oxygen-fused THP–THP