- Diethoxytriphenylphosphorane: A Mild, Regioselective Cyclodehydrating Reagent for Conversion of Diols to Cyclic Ethers. Stereochemistry, Synthetic Utility, and Scope
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Diethoxytriphenylphosphorane, Ph3P(OEt)2, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild cyclodehydration (40-110 deg C) of diols to cyclic ethers in neutral media.The regioselectivity in the closure of (S)-(+)-propane-1,2-diol and (R)-(-)-pentane-1,4-diol with Ph3P(OEt)2 is high (81-82 percent) while the cyclodehydration of (S)-(+)-phenylethane-1,2-diol gives racemized (+/-)-styrene oxide.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively with Ph3P(OEt)2.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes (or ?-dioxyphosphoranes) in the presence of Ph3P(OEt)2, and, depending on conditions, the 1,3,2-dioxaphospholanes are selectively converted to epoxides, ketones or allylic alcohols.The carbonyl compounds arise from 1,2-hydride and 1,2-methyl migrations; the allylic alcohols are derived from thermolytic eliminations. trans-1,2-Cyclohexanediols afford essentially quantitative yields (>95 percent) of the cyclohexene oxides while cis-1,2-cyclohexanediol gives the stable 1,3,2-dioxaphospholane with Ph3P(OEt)2 which decomposes under thermal conditions to cyclohexanone (90 percent).Ph3P(OEt)2 is extremely useful for conversion of "sensitive" 1,2-diols to acidic and /or thermally labile epoxides as demonstrated by the quantitative conversion of 9,10-dihydro-trans-9,10-phenanthrenediol to 9,10-dihydrophenanthrene oxide and 2α,10-pinanediol to 2α,10-epoxypinane.
- Robinson, Philip L.,Barry, Carey N.,Kelly, Jeffery W.,Evans, Slayton A.
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p. 5210 - 5219
(2007/10/02)
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- Fourier Transform Infrared Studies of the Self-Reaction of C2H5O2 Radicals
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Product studies were made with the FT IR method in the photooxidation of C2H5N2C2H5 and in the Cl-atom initiated oxidation of C2H6 in O2-N2 mixtures at 700 torr and 298 K.The major products were CH3CHO, C2H5OH, and C2H5O2H in both systems.A weak, broad band centered at 1040 cm-1 was assigned tentatively to C2H5O2C2H5.The results are consistent with the occurrence of three channels for the self-reaction of C2H5O2 radicals, i.e., 2C2H5O22C2H5O+O2 (a), CH3CHO+C2H5OH+O2 (b), C2H5O2C2H5+O2 (c), followed by the secondary reactions C2H5O+O2CH3CHO+HO2, HO2+C2H5O2C2H5O2H+O2, and 2HO2H2O2+O2.The ratios of the rate constants for reactions a-c were determined to be ka/kb=1.3 and kc/kb=0.22.
- Niki, H.,Maker, P. D.,Savage, C. M.,Breitenbach, L. P.
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p. 3825 - 3829
(2007/10/02)
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