Titanium‐Catalyzed Hydroaminoalkylation of Ethylene

Abstract

The first examples of titanium‐catalyzed hydroaminoalkylation reactions of ethylene with secondary amines are presented. The reactions can be achieved with various titanium catalysts and they do not require the use of high pressure equipment. In addition, the first solid‐state structure of a titanapyrrolidine that is formed by insertion of an alkene into the Ti−C bond of a titanaaziridine is reported.

Intermolecular Hydroaminoalkylation of Propadiene

“…Noteworthy, attempts to release the hydroaminoalkylation products from the mixture of the titanapyrrolidines 30 and 31 by simple hydrolysis (wet CH 2 Cl 2 , rt, 1 h) or heating failed. This finding is again in sharp contrast to a recent study with a titanapyrrolidine obtained from 29 and ethylene from which the hydroaminoalkylation product could easily be released in the presence of wet CH 2 Cl 2 [9] …”

“…Recent advances report both the successful use of industrially important small amines (e.g. dimethylamine) [8] and ethylene [9] in this reaction and the performance of this reaction under milder conditions and in significantly shorter reaction times [10] . Another highly desirable continuation in the field of hydroaminoalkylation reactions is the extension of the unsaturated substrate scope to compounds beyond alkenes to gain access to novel functionalized amine scaffolds.…”

“…To get insights into the possibility of a migratory insertion reaction of propadiene ( 2 ) into the Ti−C bond of a titanaaziridine, the reaction of the model titanaaziridine 29 with 2 was performed (Scheme 6), which smoothly gave access to the expected titanapyrrolidines 30 and 31 in 73 % combined yield. Titanaaziridines of type 29 are known to lack any catalytic activity in hydroaminoalkylation reactions and are therefore perfectly suited for the synthesis and characterization of stable five‐membered intermediates of the expected catalytic cycle [9, 18] . Due to similar solubility properties of 30 and 31 in polar and non‐polar solvents (e.g., n ‐hexane, tetrahydrofuran, benzene), 30 and 31 could not be separated.…”

“…This findingi sa gain in sharp contrastt oarecent study with at itanapyrrolidine obtained from 29 and ethylene fromw hich the hydroaminoalkylation product could easily be released in the presence of wet CH 2 Cl 2 . [9] In summary,s uccessful intermolecular hydroaminoalkylation reactions of propadiene with secondary amines giving access to allylamines could be achieved for the first time. While best results were obtained with various N-aryl-and N-alkyl-substituted benzylamines using the aminopyridinato titaniumc atalyst IVa,d ialkylamines, N-alkyl anilines and especially N-methylaniline turned out to be poor substrates.…”

“…Titanaaziridines of type 29 are known to lack any catalytic activity in hydroaminoalkylation reactions and are therefore perfectly suited for the synthesis and characterization of stable fivemembered intermediates of the expected catalytic cycle. [9,18] Due to similars olubility properties of 30 and 31 in polar and non-polar solvents (e.g., n-hexane, tetrahydrofuran, benzene), 30 and 31 couldn ot be separated. However,r esults obtained from multinuclear and 2D NMR spectroscopy unambiguously allowed for the assignment of the connectivity (Figures S60-S63).…”