N-(1-acyloaminoalkyl)amidinium salts derived from DBU or related bases as reactive intermediates in α-amidoalkylation reactions

Katarzyna Piernikarczyk,Roman Mazurkiewicz,Jakub Adamek,Agnieszka Pazdzierniok-Holewa,Katarzyna Zielińska,Gyorgy Hajos

doi:10.3998/ark.5550190.0013.423

Abstract

N-Acylamino)alkyltriphenylphosphonium salts 4, when treated with DBU, DBN or TBD in CD3CN or MeCN, were transformed immediately into the corresponding 1-(N- acylamino)alkylamidinium or guanidinium salts 5. Salts 5 with a proton at the α-position underwent slow transformation to the corresponding enamides 6. 1-(N- Acylamino)alkyltriphenylphosphonium salts 4, amidinium or guanidinium salts 5, as well as enamides 6 reacted readily with β-dicarbonyl compounds in the presence of corresponding base under microwave irradiation at 60 o C to give the expected product of α-amidoalkylation of the enolate anion. The role of 1-(N-acylamino)alkylamidinium or guanidinium salts 5 as reactive intermediates in α-amidoalkylation with 1-(N-acylamino)alkyltriphenylphosphonium salts is discussed.

Highlights

1-(N-Acylaminoalkyl)triphenylphosphonium salts 4a-j (Table 1) reacted immediately with DBU, DBN or TBD in MeCN or CD3CN, which allowed the reaction to be monitored directly by 1H NMR spectroscopy
In the present communication we report our investigations of some unexpected reactions of phosphonium salts 4 with DBU and related bases (e.g., DBN or TBD), which generate the corresponding N-(1-acylaminoalkyl)amidinium or N-(1acylaminoalkyl)guanidinium salts
High-resolution mass spectroscopy with ESI-ionisation of the obtained compounds revealed that, in all of the cases, the molecular formula of the molecular ion matched the cation of the corresponding N-(1-acylaminoalkyl)amidinium or N-(1-acylaminoalkyl)guanidinium salts 5 formed by amidoalkylation of DBU, DBN or TBD (Scheme 3, Table 1)

Summary

Introduction

1-(N-Acylaminoalkyl)triphenylphosphonium salts 4a-j (Table 1) reacted immediately with DBU, DBN or TBD in MeCN or CD3CN, which allowed the reaction to be monitored directly by 1H NMR spectroscopy. Scheme 4 Investigations on this reaction are in progress; it is evident that compound 7 results from a novel aza-Morita-Baylis-Hillman-like reaction between the corresponding Nacylimine (as the electrophilic component) and N-deprotonated amidinium salt 5h (as the nucleophilic component).[42] It seems, that dimer 7 is formed mainly during the work-up of the reaction mixture, as the isolated yield of this compound is much higher than its contents in the reaction mixture before the work-up.

Results

Conclusion