Base-promoted reactions of epoxides. VI. Bicyclo[2.2.1]heptene and bicyclo[2.2.2]octene oxides

Abstract

The details of the previously observed lithium diethylamide isomerization of 2,3-epoxybicyclo [2.2.1] heptane to nortricyclanol have been examined. By deuterium labeling methods, it has been shown that reversible metalation occurs a t the epoxide ring and that base attack does not remove the ex0 hydrogens of the transannular bridge.The endo-5-methyl derivative 5 is transformed into the analogous tricyclic alcohol 7, whereas epoxide 6, with both transannular endo positions blocked with methyl groups, isomerizes to bicyclic ketone 9. Bornylene oxide gives camphor, epicamphor, and tricyclic alcohols 13 and 14. 2,3-Epoxybicyclo [2.2.2]octane gives ketone 19 along with minor amounts of tricyclic alcohol 20. 2,3-Epoxybicyclo[3.3.0]octane yields allylic alcohol 25 as well as lesser amounts of ketones 23 and 24. These results are used to outline the scope of the base-promoted isomerization of epoxides as a source of products derived from carbenoid insertion into transannular C-H bonds.These observations support a carbenoid mechanism for the rearrangement.

Oxiranyl Anions and Aziridinyl Anions

“…Heating of norbornene oxide ( 79 ) with lithium diethylamide in benzene gave nortricyclanol ( 80 , Scheme ) . The carbenoid mechanism of this reaction was confirmed by using deuterium-labeled epoxide 81 . When epoxide 81 was treated under the same conditions, nortricyclanol 83 was obtained and it was found that all the deuterium label was retained.…”

Reactivity of Oxiranes with Organolithium Reagents

“…The predominance of this pathway over other possible pathways has been attributed to conformational properties of the lithiooxirane intermediate 5,26 ; for the same reason, this predominance can be precluded for substituted medium-size oxiranes 244 . This reaction is also widely observed in the case of bicyclic oxiranes where Bredt's rule and the blocked conformation (see Section II.A) precludes the allylic alcohol formation, such as norbornene oxide 17 254,255 . However, it has been very seldom reported in the case of linear oxiranes 256 .…”

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

“…This epoxide is known to give the 1,3-carbenoid C-H insertion product (alcohol 40) upon treatment with organolithium reagents (Scheme 9). [36,[40][41][42] Scheme 9.…”