The four isomers of 2,3,5‐trimethylmorpholine and those of 2,3,6‐trimethylmorpholine have been synthesized from appropriately substituted ethanolamines and separated by means of preparative gas‐liquid chromatography. The configuration of each isomer was determined from 270 MHz FT‐nmr studies of the magnitudes of the methine‐methine and methine‐methylene proton coupling constants. The evaluated chemical shifts of axial methyl groups are discussed.
Treatment of (S:R)‐N‐benzyl‐1,1′‐iminobis‐2‐butanol with 70% w/w sulfuric acid gives cis‐ and trans‐N‐benzyl‐2,6‐diethylmorpholines (15 and 74%, respectively) and N‐alkenyl‐4‐ethyl‐1,2,3,4‐tetrahydroisoquinolines (5%). Hydrogenation of the reaction mixture gives cis‐ and trans‐2,6‐diethylmorpholines and N‐butyl‐4‐ethyl‐1,2,3,4‐tetrahydroisoquinoline. Neither N‐benzyl‐N‐crotyl‐(2‐hydroxy‐1‐butyl)amine (4) nor N‐benzyldicrotylamine (5) are intermediates in the reaction. (S:S)‐N‐Benzyl‐1,1′‐iminobis‐2‐butanol gives 95% of cis‐N‐benzyl‐2,6‐diethylmorpholine and 1% of the trans isomer.
The mechanism of cyclization of 3,3′‐iminobis‐2‐butanols to 2,3,5,6‐tetramethylmorpholines in sulfuric acid is studied. Contrary to our prior suggestions, the ring closure seems to be exclusively a normal S N 2‐type substitution. The partial inversion before the cyclization is discussed.
2‐Butenoxid (I) reagiert mit Ammoniak zum Aminoalkohol (II), der mit weiterem (I) das sekundäre Amin (III) gibt und dann zum Tetramethylmorpholin (IV) cyclisiert werden kann.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.