N-(1-Acylaminoalkyl)amidinium salts derived from DBU or related bases as reactive intermediates in .-amidoalkylation reactions
Agnieszka Pa.dzierniok-Holewa, Jakub Adamek, Katarzyna Zieli.ska,
Katarzyna Piernikarczyk, and Roman Mazurkiewicz*
Department of Organic and Bioorganic Chemistry and Biotechnology, Silesian University of
Technology, Krzywoustego 4, PL 44-100 Gliwice, Poland
E-mail:
[email protected]
Dedicated to Prof. Pawe. Kafarski in honor of his life time achievements in chemistry
---
Abstract
1-(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 .-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 .-dicarbonyl compounds in the presence of corresponding base under microwave irradiation at 60 oC to give the expected product of .-amidoalkylation of the enolate anion. The role of 1-(N-acylamino)alkylamidinium or guanidinium salts 5 as reactive intermediates in .-amidoalkylation with 1-(N-acylamino)alkyltriphenylphosphonium salts is discussed.
Keywords: 1-(N-Acylamino)alkyltriphenylphosphonium salts, 1-(N-acylamino)alkylamidinium salts, .-amidoalkylation, N-acylimines, enamides, non-nucleophilic bases
---
Introduction
N-Acylimines 2 and N-acyliminium cations 3 are highly reactive short-lived intermediates of many important transformations in organic synthesis, notably, the .-amidoalkylation of a wide variety of O, N, S, P and C-nucleophiles.1-5 Most frequently, N-acylimines or N-acyliminium cations are generated in situ from .-substituted N-alkylamides with a nucleofugal leaving group Z at the .-position by a base-catalysed .-elimination of HZ (to give the N-acylimine) or by an acid-catalysed loss of the Z group (to give the N-acyliminium cation) (Scheme 1).1,6-8
