Proximity Effects. XII. Reaction of cis- and trans-Cycloöctene Oxide with Bases

Organic reactions at alumina surfaces. Mild and selective opening of epoxides by alcohols, thiols, benzeneselenol, amines, and acetic acid

“…T h e results obtained in the reaction of to those for cyclohexene oxide, except that the reaction of cycloheptene oxide with n-butylamine-doped alumina required 24 h for completion. Medium-ring (8)(9)(10)(11)(12) cycloalkene oxides a r e much less reactive than cyclohexene oxides and are difficult to open homogeneously to only 2-functionalized cycloalkanols; direct 1,2-epoxide opening is usually accompanied by substantial amounts of side products derived from transannular interactions. * For example, cyclooctene oxide is inert to refluxing alcoholic sodium methoxide and sodium ethoxide,1° and solvolysis of cyclooctene oxide gives products arising from transannular 1,3-or 1 $hydride shifts (eq S).l cis-Cyclodo-0 1 ; qoA (8) NaOAc/HOAc OAc 45% 0 6 0°C .…”

“…Even acetic acid on alumina produced Al2O3 4% (W-ZOO-N-D) RZH -d' l i " (10) the corresponding secondary acetate regiospecifically as the only observed product; no allylic alcohol was detected. Unsymmetrical steroidal epoxide 6 reacted with benzeneselenol-doped alumina to give trans hydroxyselenide 7 regiospecifically and stereospecifically (eq 1 1).…”

“…-m yield10 Olefinic epoxide 10 has been reported to react with lithium diethylamide to give the mixture of cyclooctene derivatives Journal of the American Chemical Society / 99:2.December eq 12;13 in contrast, n-butylamine-doped alumina produced analytically pure trans amino alcohol 11 in 68% chromatographic purification. Likewise, in sharp contrast to homogeneous acidic solvolysis of olefinic epoxide 10 which gave bicyclic products in 20% yield, acetic acid doped alumina gave no bicyclic products (eq 13).…”

Reactions of steroidal 4,5- and 5,6-epoxides with strong bases

“…Pres~imably, the steric bulk of these reagents prevents hydrogen abstraction in the cases studied. The failure to observe any rearrangements resulting from a hydrogen abstraction (14)(15)(16) by LDA may also be attributable to steric factors. Since reactions with LDA co~ild be carried out only at low temperatures (17), further experii~~ents used the more versatile diethyl amide LDEA.…”

Organolithium/Chiral Lewis Base/BF3: a Versatile Combination for the Enantioselective Desymmetrization of meso‐Epoxides

“…We have already observed that the cyclooctene oxide 24 Scheme 5. provides a mixture of the expected arylcyclooctanol 32 and the (-)-endo-cis-fused bicyclic alcohol 34, as a single diastereoisomer, under our reaction conditions with PhLi. [27,28] This latter compound was first obtained by Cope, [29] starting from the same epoxide and using strongly basic conditions (LiNEt 2 , boiling Et 2 O, 48 h), and was rationalized as a result of an α-deprotonation followed by a transannular C-H insertion of the transient carbenoid species. [30][31][32][33] In our conditions at -78°C, using stronger bases than PhLi and in diethyl ether instead of toluene, the reaction was chemoselective, yielding exclusively the rearranged alcohol 34 in quantitative yields (Scheme 5).…”