Novel nitrosation of cyclic N-alkyl enamines

TetrsbedronLetters

NOVEL NITROSATION

Departamento

in &eat

Britain.

OF CYCLIC N-ALKYL ENAMINES'

G.A.L. Ferreira,

J.R. Mahajan*,

Printed

Pergamon Prerr.

35, pi 3025 - 3028, 1974.

NO.

de Quimica, Universidade

H.C. AraGjo and B.J. Nunes

de Brasilia,

Brasxlia-DF,

Brasil

(Receivedin USA 15 October 1973; received in UK for publication11 July 1974) We have recently reported the synthesis of oximino-macrolides acetyl oximino-lactams cyclic enol-ethers

by the hydrolytic

and N-acetyl

nitrosation

enamines. 2,3

of the

and

corresponding

In contradistinction,

the

4 same reaction when attempted with the cyclic W-ethyl enamines(I), ed the oximino enamines(IV) Only once, in one case isolated,

yield-

instead of the desired oximino-lactams(III).5

(I,n=2), has the oximino-lactam(III,n=2)

been

also

although in very low yield.

The new compounds were characterized and

N-

1 6 H n.m.r. spectra.

by elemental

Some of their physical

data are recorded

ble 1. The n.m.r. spectra of oximino-enamine(IV,n=2) 1 for quick inspection.

is reproduced

in the reaction behaviour

mines is due to their increased basicity The first reaction

formation of the N-nitrosoammonium

in fig.

troso group to the C-atom bearing

homo-

respectively. of the N-alkyl

over the N-acetyl

ena-

analogs

and

in the present series seems to be ion

(A), which then transfers

a 1:3 &

relationship

to it

the

In accordance with expectation,

ture(V)4 proved unreactive

towards nitrosation'

on elaboration

of the reaction mixture.

ne mixture(V1)

reacted normally

In contrast, the N-acetyl

to furnish the expected

3025

ni-

to

the enamine

and was largely

the

(see sche_

me). To check this point of view, the peri position was substituted prevent oxime formation.

ta-

to fig. 1; the saturated methyl-

having 2 and 4 more hydrogens,

The drastic difference

the enol-ethers.

in

The n.m.r. spectra of other oximino-enamine

logs(IV; n=3 and 4) show broad similarity ene region(Sl.S-2.0)

i-r.

analysis and

mix-

recovered enami -

oximino-lactam(VII).

3026

Evidently, the behavior of N-alkyl enamines towards nitrosation like that of the tertiary amines.'

Smith and Loeppky have

demonstrated

the formation of N-nitrosoammonium salts in the nitrosation of amines.7a

iS

tertiary

In the present case, a circumstantial evidence for N-nitrosa

tion was the immediate appearance of yellow colour instead of the as noticed in our earlier studies involving C-nitrosation.2,3

blue,

Moreover,

tertiary amines in highly acidic solution (pH below 3) and

quaternary ammonium salts are known to be unreactive towards nitrosation.7 Accor-

dingly, in the present case, the nitrosation failed in solutions with pH below 3 and the starting material could be recovered, though with a considerable work-up loss. In nitrosation experiments conducted with

1.1

equivalen'tof perchloric acid, the perchlorate of enamine (I; n=2: color less needles, m.p. 240-241°; max.(KBr)1672 and 1087 cm-') could be direc tly isolated after evaporation of the nitrosation mixture. It is tempting to assume that the reaction proceeds through the

iso-

merit form (II), but there was no detectable evidence (n.m.r.) for

its

presence in the starting material even after refluxing for a couple

of

hours in chloroform or ethanol, containing acid or base. Nitrosation studies at different controlled pH as well as those rected to shed more light on the mechanismof the reaction are under

diway

and will be reported in the detailed publication. TABLE

Compound (IV;n=2)

M.P.

151-152O

125-127O

101-103°

C12H20N203

3135,1631,1610

Found:69.11; 9.49; 13.63

3226,1631,1618

Found:70.30; 9.82; 12.44

3175,3067,1656,1634

Calcd:70.23; 9.97; 12.60

C13H22N20 (VII)

Found:67.95; 9.11; 14.27

umax.(cm-+

Calcd:69.19; 9.68; 13.45

C12H20N20 (IV;n=4)

;H;N%

Calcd:68.01; 9.34; 14.42

C11H18N20 (IV;n=3)

C

1

140-142O

Found:59.72; 8.14; 11.48 Calcd:59.98; 8.39; 11.66

3344,1724,1661,1550

l?O.

3027

35

ll=2-4

i (B)

f’ d y5

-(

a n

w

3028

REFERENCES AND NOTES

1.

G.A.L. Ferreira, S.B.P.C.,

J.R. Mahajan, H.C. de AraGjo e B.J. Nunes,

Ci&cia

2. J.R. Mahajan,

Resumos

e Cultura, 25, 118 (1973).

G.A.L. Ferreira,

and H.C. Araiijo, Chem. e.,

1078

(1972). 3. J.R. Mahajan, G.A.L. Ferreira, H.C. Arafijo, and B.J. Nunes, Synthe*,

313 (1973).

4. The N-ethyl enamines

enamines were prepared

(ref. 3) by reduction with Li.A1H4. Enamine

as a 17:83 mixture 5. The nitrosation equimolar

from the corresponding

(n.m.r.) of the

experiments

quantities

dioxane solution,

*8'9_ :

N-acetyl

(V) was obtained

,9,10_ compound.

were conducted between

10 to 25O

using

of the enamine and n-butyl nitrite in aqueous

containing

a drop or two of 10% hydrochloric

acid

(pH ca. 8-9). 6. The infrared spectra trument. The instrument.

(KBr disc) were taken on a Perkin Elmer 137 ins

1 H n.m.r. spectra The elemental

(CDC13) were taken on a Varian A60-D

analysis were carried out by

Alfred Bern-

hardt, West Germany. I. (a) P.A.S. Smith and R.N. Loeppky, g. &I. s. (b) G.E. Hein, J. -Chem. Eudc., iI, tribe an instructive about the nitrosation

E.,

181 (1963). These two papers des-

account of the over a century-old of tertiary

83,1147(1967);

amines.

controversy