Science of Synthesis

Abbaspour Tehrani, K.; De Kimpe, N., Science of Synthesis, (2004) 27, 318.

The reaction of non-enolizable aliphatic and aromatic aldehydes with N-(trimethylsilyl)pyrrolidines or -morpholines provides an alternative synthesis of ternary iminium salts ‌12‌ (‌Scheme 4‌).[‌35‌,‌36‌] This reaction proceeds via the addition of the silylamine to carbonyl compound ‌10‌ followed by chlorotrimethylsilane-induced ether cleavage of the resulting unstable α-(trimethylsiloxy)amine ‌11‌. However, when enolizable carbonyl compounds are reacted under these conditions, enamines are obtained. In order to avoid this problem, the more efficient ether cleavage reagent trimethylsilyl trifluoromethanesulfonate is used. In this way, a whole range of N-benzylidenepyrrolidinium trifluoromethanesulfonates has been prepared.[‌25‌,‌37‌] [It should be noted that, in some examples, pyrrolidinium trifluoromethanesulfonate (up to 30%) was present as an irremovable impurity.] However, the reaction of N-silylated morpholine, piperidine, or diethylamine with substituted benzaldehydes using the same conditions provides only a small amount of the corresponding iminium trifluoromethanesulfonate salt, while the reaction with ketones does not proceed.[‌25‌] Another limitation of this method is unavoidable epimerization when chiral carbonyl compounds are used.[‌25‌] By treating 3,3-dichloroprop-2-enal (‌13‌) with N-(trimethylsilyl)amines and chlorotrimethylsilane, a mixture of N,N-dialkyl-3,3-dichloroprop-2-eniminium chlorides ‌14‌ and N,N-dialkyl-3-amino-3-chloroprop-2-eniminium chlorides ‌15‌ is obtained.[‌38‌] Compound ‌14‌ (R1 = Me) is the vinyl analogue of dichloro-N,N-dimethylmethaniminium chloride, Viehe's salt.

‌Meeeee 8‌ Meeeeeee ee M-(Meeeeeeeeeeeee)eeeeee ee Meeeeeee Meeeeeeee[‌88‌,‌88‌,‌88‌]

‌Meeeeeeeeee 8‌

Meeeeeeeeeee Meeeeeeee

8-Meeeeeeeeeeeeeeeeeeeeeee Meeeeeee (‌88‌, M8 = Me; M8 = M; MM88 = Meeeeeeeee-8-ee; M = Me):[‌88‌]

Meeeeee eeeeeeeee M-(eeeeeeeeeeeeee)eeeeeeeeeee (8.88 e, 88 eeee) eee MMMMe (8.88 e, 88 eeee) eeee eeeeeeeeeeee eeeee ee ee ee e eeeeeee eeee ee eeeeeeeeeeee (‌88‌, M8 = Me; M8 = M; 8.88 e, 88 eeee) ee eee Me8M (88 eM) eeeee eeeee eeeeeeeeee. Mee eeeeeee eeee eeeeeeeeeeee eeeeeeeeeee, eee eeeee eeeeeeee eee eeeeeeee eeee eeeeeeeee ee eeeeeeeeee eeeee eeeee eeeeeeeeee, eeeeee eeee eee Me8M (8 × 8 eM), eee eeeee; eeeee: 8.88 e (88%). (Meee: Mee eeeeeee eeeeeeeeee eeee eeeeeee.)

References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) M 88e8, 888.