Fifth International Electronic Conference on Synthetic Organic Chemistry (ECSOC-5), http://www.mdpi.org/ecsoc-5.htm, 1-30 September 2001
[E0001]

Rearrangement of ammonium ylides under microwave irradiation

Séverine Torchy, Guy Cordonnier and Didier Barbry*

Laboratoire d’Ingénierie Moléculaire, Université des Sciences et Techniques de Lille, F-59655 Villeneuve d’Ascq (France)
Tel. / Fax +33 (0)320 434974, E-mail: [email protected]

Received: 15 August 2001 / Uploaded 22 August 2001

Abstract : Ammonium ylides rearrangement is carried out using microwave irradiation or conventional heating. A strong microwave effect is noticed.
Keywords : Ammonium ylide rearrangement, microwave irradiation 

Introduction

Ammonium ylides can be generated by treatment of ammonium salts with strong bases1, or with cesium fluoride (non-basic medium) when the ammonium bears a trimethylsilylmethyl group2. These ylides isomerise to (1,2) rearrangement products or to (2,3) shift products when allyl or benzyl substituents are located on the nitrogen atom (in some cases, (1,4) rearrangement has been also reported).

The Sommelet-Hauser rearrangement is a (2,3) sigmatropic shift whereas the Stevens rearrangement may follow one of three processes :

In this work, we describe the evolution of ammonium ylides under microwave irradiation and we compare their behaviour under conventional heating.
  Ammonium salts were obtained from N,N-dimethylbenzylamine for entries 1, 2 and 5 , from N,N-dimethylallylamine for entry 3 and from N-benzyl, N-methylphenacylamine for entry 4. Yields are excellent for entries 1 and 3 ; in the other cases, the oily products were directly used in the rearrangement reactions to limit their decomposition. All the compounds gave nmr spectra in agreement with their structure. The ammonium salts are treated in a focused microwave reactor (45W; Synthewave 402) with 1.25 equivalent of a 10 % solution of sodium hydroxide, except for entry 5 (benzylcyanomethyldimethylammonium chloride). In that latter case, we used sodium methanolate in dimethylformamide to avoid degradation of the cyano group as noticed by Stevens3. The results were compared with those obtained with similar temperature rising using conventional heating (Scheme).
 
 

Scheme – Temperature rising (Table 1, entry 1) using microwaves and conventional heating





The rearrangement of ammonium ylides is especially related to the following parameters : steric hindrance of nitrogen substituents, temperature, medium polarity and strength of the base.
 
 
 
AmmoniumSalt
Yield %
Rearrangement product
Reaction time (min)
Yield

(Microwaves)

%
Yield

(Conventional heating) %

1
90
2
95
15
2
58
3
63
5
3
96
1.5
98
46
4
45
1.5
94
76
5
51
2
69

(A:B 70:30)
56

(A:B 10:90)

Table – Ammonium salts formation and ammonium ylides rearrangement under microwave irradiation or using conventional heating.
 

We isolated the same products under microwave irradiation and by classical heating. In particular, the benzyl group has a larger ability to migration than the allyl group and mixtures of products are obtained in the case of the entry 5.

However we have noticed a strong microwave effect: in all cases the reactions are faster and microwave irradiation promotes the Stevens reaction while conventional heating favours the (2,3) shift in benzylcyanomethyldimethylammonium ylide. Studies are in progress to explain that particular behaviour and to perform the tandem ammonium salt formation-ylide rearrangement under microwave irradiation with a-aminonitriles4 and a-aminoesters5.
 
  1. Pine, S.H. Org. React. 1970, 18, 403-464.
  2. Nakano, M. ; Sato, Y. J. Org. Chem. 1987, 52, 1844-1847.
  3. Paton, J.M. ; Pauson, P.L. ; Stevens, T.S. J. Chem. Soc. 1969, 2130-2131.
  4. Stella, L. ; Amrollah-Madjdabadi, A. Synth.Commun. 1984, 14, 1141-1147.
  5. Coldham, I. ; Middleton, M.L. ; Taylor, P.L. J. Chem. Soc. Perkin Trans. 1 1998, 2817-2821.