Nitration by oxides of nitrogen, part 3: Reactions of dinitrogen pentoxide with mono- and dioxacycloalkanes with 5-, 6- & 7-membered rings

Tetrahedron Printed in

Letters,Vol.30,No.46,pp Great Britain

6431-6434,1989

NITRATION BY OXIDES OF NITROGEN, PART WITH MONO- AND DIOXACYCLOALKANES

0040-4039/89 $3.00 Pergamon Press plc

3: R E A C T I O N S W I T H 5-, 6-

+

.OO

OF DINITROGEN PENTOXIDE & 7-MEMBERED RINGS

p Golding, R W Millar*, N C Paul and D H Richards (deceased) Ministry of Defence, R.A.R.D.E., Powdermill Lane, Waltham Abbey, Essex EN9 lAX. Reaction of m e d i u m ring cyclic ethers with N205 in halogenated solvents gave only low yields of the corresponding dinitrates. On the other hand, cyclic formals (1,3dioxolane and its homologues) gave moderate yields of unstable ring-opened products (hemiformal nitrates), together with variable amounts of rearranged products containing formate ester groups. The formates are believed to result from attack of N205 on the heterooycle by a hydride abstraction route. We have reported previously I that dinitrogen pentoxide (N205) cleaves small-ring (3- & 4-membered) oxygen heterocycles, i.e. epoxides and oxetanes, to form the corresponding nitrate ester derivatives (1,2- or 1,3-dinitrates) in high yield. The driving force for the reaction is release of ring strain in the heterocycle, and the ring cleavage proceeds rapidly with simple substrates, that is, those not bearing other ring substituents. We wished to extend the scope of this reaction to other, larger, ring systems, in particular cyclic ethers such as tetrahydrofuran (THF, i) and oxepane (i), and dioxa-analogues of the 5-, 6- & 7-membered systems (dioxolanes, dioxanes and dioxepanes, as their 1,3-isomers, ~ , ~ & ~). In addition, some related compounds were

CL 0V

X

O~

X

0v

X

X = C H 2, !

X = C H 2, 2

X = C H 2, 3

X=O,

X=O,

X=O,

4_

5

6

briefly studied - a linear formal, and two 2-substituted 1,3-dioxolanes (see later). Comparisons of conventional ring strain energies (CRSEs) 2 indicated that the cyclic ethers, THF and oxepane, although possessing lower ring strain (CRSEs 23 & 33 kJmol -I respectively) than their small-ring homologues (CRSEs ca Ii0 kJmol-l), might react similarly to the epoxides and oxetanes, although more sluggishly. The dioxa-analogues were selected for study on account of their ready availability and the possibility of providing a convenient synthesis of the hemiformal nitrate (-O-CH2-ONO 2) group, accessible only with difficulty by known methods 3-5. We now report that reaction 6 of the cyclic ethers THF and oxepane with N205 gave only small amounts of the corresponding ~,~-dinitrates (I & ~), detected by hplc 7, after reaction periods of several hours (cf minutes for small-ring compounds), and also they

O2N O -

(CH2) 4 -- O N O 2

O 2 N O - - (CH2) 6 - - O N O 2

Z were minor components of complex mixtures which contained and/or oligomerisation products (the presence of aldehyde was inferred from the i.r. and nmr spectra of the product examination of the reaction of the six-membered homologue

6431

predominantly oxidation and carboxylic acid products mixtures). A brief (tetrahydropyran, ~)

6432

indicated that no ~ , ~ - d i n i t r a t e was formed, with m u c h u n c h a n g e d s t a r t i n g m a t e r i a l remaining after a m u l t i - d a y reaction period, in c o m p l e t e a c c o r d with the very low ring strain of this substrate. Therefore the reaction of such m e d i u m - r i n g oxygen h e t e r o c y c l e s with N205 does not c o n s t i t u t e a useful m e t h o d for the p r e p a r a t i o n of ~ , ~ dinitrates. T u r n i n g to the d i o x a c y c l o a l k a n e s , we f o u n d that, in the case of the cyclic formals (i.e. f o r m a l d e h y d e acetals) 1 , 3 - d i o x o l a n e (~), 1,3-dioxane (~) a n d 1 , 3 - d i o x e p a n e (~), a more rapid reaction took place 6 (essentially c o m p l e t e within several hours) to y i e l d the e x p e c t e d ring c l e a v a g e products, n a m e l y the h e m i f o r m a l n i t r a t e s 4, I0 & 118 , but v a r y i n g amounts of u n e x p e c t e d p r o d u c t s r e s u l t i n g from a c o m p e t i n g ring cleavage/ o x i d a t i o n reaction, n a m e l y the formates 12, 13 & 149 , were also obtained. The formation of such products, which was most p r o n o u n c e d in the case of 1,3-dioxolane, is b e l i e v e d to involve as the initial step a h y d r i d e a b s t r a c t i o n b y N205 f r o m the bridging m e t h y l e n e g r o u p to give d i o x o l e n i u m ions of type 15, which r e a r r a n g e to give the o b s e r v e d p r o d u c t s (see Scheme). Hydride a b s t r a c t i o n s f r o m 1 , 3 - d i o x o l a n e s are well known I0 but n o r m a l l y are i n d u c e d b y common Lewis acids (BF3, t r i t y l salts II (e.g.

ring

O2NO--CH2CH 2 - O - - C H 2 - ONO 2

9

o./o

N2Os

F-Z

NO2 +

4

0~0

. HNO 2

H

,

/

%I

% %

., ~ (CH2)n

CH2CH 2 -- O _ C OO

I

H

15

N O 3"

O2NO-CH2CH 2 - O - C~~O H 12

Scheme

6433

O2NO(CH2)nOCH2ONO2 n=3, n=4,

O2NO(CH2)nOCHO

10 11

n=3, n=4,

O2NOCH2OCH2ONO 2

13 14

16 -

-

Ph3C+BF4 -) etc); the reaction r e p o r t e d here is the first case, to our knowledge, of a h y d r i d e a b s t r a c t i o n i n d u c e d by N205. In the case of Lewis a c i d initiated o l i g o m e r i s a t i o n s / p o l y m e r i s a t i o n s , g e n e r a t i o n of formate e s t e r t e r m i n a l groups from d i o x o l a n e is well e s t a b l i s h e d 12. The ratios of the h e m i f o r m a l n i t r a t e and formate products in the above reactions were also interesting, and c o r r e l a t e d with ring size, most formate b e i n g o b t a i n e d with d i o x o l a n e and least with the six- and 3 e v e n - m e m b e r e d h o m o l e g u e 3 (as e v i n c e d by IH nmr integral m e a s u r e m e n t s ) . This is b e l i e v e d to result from the r e l a t i v e stabilities of the i n t e r m e d i a t e cations, with the f i v e - m e m b e r e d case, b e i n g p l a n a r or near-planar, d e l o c a l i s i n g c h a r g e m o r e e f f e c t i v e l y than the n o n - p l a n a r six- a n d s e v e n - m e m b e r e d intermediates. It s h o u l d also be m e n t i o n e d that the product m i x t u r e s which c o n t a i n e d a high p r o p o r t i o n of h e m i f o r m a l nitrates were unstable, even a f t e r t h o r o u g h washing to remove traces of acid; this i n s t a b i l i t y is in a c c o r d with the r e p o r t e d properties of other c o m p o u n d s of this class (e.g. 16), which are known to d e f o r m y l a t e readily 4 . Interestingly, an a c y c l i c formal, d i - n - b u t y l formal (17), when reacted with N205 under

N2Os (Buno)2CH2

~

17

BunoNo2

+

BunocH2ONO2

19

18

similar c o n d i t i o n s y i e l d e d a hemiformal nitrate, 1813 , (together with butyl nitrate ( ~ ) as co-product) but no formate, i n d i c a t i n g that the h y d r i d e a b s t r a c t i o n route makes no c o n t r i b u t i o n in this case, in agreement with the ring size trends noted above. Finally, the e f f e c t of b l o c k i n g the 2 - p o s i t i o n of the d i o x o l a n e ring was b r i e f l y investigated, by e x a m i n i n g the reactions of the cyclic ketal, 2 , 2 - d i m e t h y l - l , 3 d i o x o l a n e (2_Q) and the c o r r e s p o n d i n g acetal (21) with N205. The ketal reacted

~

0~0 Me 2O

Me

O2NOC(Me)2OCH2C HO

0~0 H Me 2=3

22 O2NOCH(Me)OCH2CHO 23

0 ._~0 Me 24

s l u g g i s h l y to p r o d u c e a v a r i e t y of products, amongst which was a c o m p o u n d with spectra consistent with an a l d e h y d e - n i t r a t e s t r u c t u r e (22) 14, b e l i e v e d to result from a hydride a b s t r a c t i o n at the 4-position of the ring, this a l t e r n a t i v e p o s i t i o n b e i n g attacked owing to b l o c k a g e of the 2-position. E t h y l e n e glycol m o n o - a n d d i n i t r a t e s were also identified (by gc-ftir) 15 as minor products. The acetal, on the other hand, b e h a v e d quite differently, with much less a l d e h y d i c product, p r e s u m e d to be 23, being observed; the p r e d o m i n a n t p r o d u c t s were oligomers p r o d u c e d by c a t i o n i c r i n g - o p e n i n g p o l y m e r i s a t i o n via the stable, l o n g - l i v e d d i o x o l e n i u m i n t e r m e d i a t e (24). Such 2m e t h y l d i o ~ o l e n i u m salts have been shown e l s e w h e r e to be i s o l a b l e in m a n y casesl0; moreover, ready o l i g o m e r i s a t i o n of 2 - m e t h y l d i o x o l a n e by strong acids such as HCIO 4 has been r e p o r t e d 16. Thus the b l o c k e d d i o x o l a n e s exhibit c h e m i c a l b e h a v i o u r s t r o n g l y dependent on the d e g r e e of s u b s t i t u t i o n on the 2-position, as expected.

6434

Acknowledcrments Thanks are due to Dr A V C u n l i f f e and Mr R M o r r e l l for r e c o r d i n g the 13C nmr spectra, and to Mr P J H o n e y for a s s i s t a n c e in r u n n i n g g c - f t i r traces. R e f e r e n c e s and Notes i. P Golding, R W M i l l a r N C Paul and D H Richards, Tetrahed. Letts., 29(22), 2731-4 (1988) 2. A R K a t r i t z k y "Handbook of H e t e r o c y c l i c Chemistry", p p 132, 134, P e r g a m o n Press, Oxford, 1985 3. H Bohme and P H Meyer, Synthesis, 207-8 (1971) 4. L T Eremenko, A M Korolev, V N G r e b e n n i k o v and G M Nazin, rzv. Akad. Nauk. SSSR, Set. Khim., 627-9 (1971); Chem. Abstr. 75 48216a 5. G V Oreshko, L B Romanova and L T Eremenko, Izv. Akad. Nauk. SSSR, Set. Khim., 2140-1 (1973); Chem. Abstr. 80 14497f 6. In a typical run, the oxygen h e t e r o c y c l e (30 mmol) d i s s o l v e d in CH2CI 2 or CDCl 3 (15 ml) was a d d e d d r o p w i s e o v e r 15 min. at -10 to 0"C to a s o l u t i o n of N 2 0 5 (35 mmol) in the s a m e solvent (25 ml). The m i x t u r e was s t i r r e d at 0 to 1 0 " C until the rate o f d i s a p p e a r a n c e of s t a r t i n g material h a d l e v e l l e d o f f (monitor b y gc or IH nmr), t y p i c a l l y 16hr, a n d the m i x t u r e was then q u e n c h e d in s a t u r a t e d N a H C O 3 solution, extracted, a n d the e x t r a c t s w a s h e d well with s a t u r a t e d N a H C O 3 s o l u t i o n a n d water. A f t e r d r y i n g o v e r a n h y d r o u s MgS04, removal of s o l v e n t a f f o r d e d the p r o d u c t mixture. •Caution: p r o d u c t s d e s c r i b e d herein a r e e n e r g e t i c c o m p o u n d s and a p p r o p r i a t e p r e c a u t i o n s s h o u l d be taken in their h a n d l i n g . ] 7. RPI8 (Merck) column, m e t h a n o l - w a t e r 60:40 eluant, 30"C, m o n i t o r at 210 nm. 8. Yield; IH nmr*; [13C nmr*]; i.r.**: ~ - 24% (53% with 150% excess N205); 5 4.0(m,2): 4.6-4.7(m, 2); 5.57(s,2); [5 66.49 (-CH-O-); 71.09 (O2NO-CH2-); 94.30 (O-CH2-ON02)] , Vma x 1640,

1283,

856 cm-l;

I0 - T; 5 2.08(t,2);

4.59(t,2);

5.55(s,2); Vma x 1635,

1286,

865 cm-l;

4.48(t,2);

5.52(s,2); Vma x 1631,

1282,

876,

3.88(t,2);

Ii - t; 5 1.79(t,4);

3.77(t,2);

836 cm -I.

9. Yield; IH nmr*; [13C nmr*]; i.r.**: 12 - 8% (17% with 150% excess N205); 5 4.64.7(m, 2); 8.13(s,i), [6 59.45 (-CH2-O-); 70.01 (O2NO-CH2-); 160.40 (-CHO)], Vma x 1730,

i~40,

1283,

Vma x 1726(m),

1173, 855 cm-l;

1637,

1283,

1157,

13 - t; 5 2.1(m, 2);

866 cm-l;

14 - t;

4.0-4o4(m, 4); 8.20(s,I);

(IH nmr s p e c t r u m not a c c u r a t e l y

m e a s u r a b l e - signals too weak); Vma x 1723(w), 1631, 1282, I157(m), 876, 836 cm -I 10.C U Pittman, S P M c M a n u s and J W Larsen, Chem. Rev. (ACS) 72 357-438 (1972) II.A Stolarczyk, P Kubisa and S Penczek, J Macromol. Sci.-Chem., 25 627 (1977) 12.S Inoue a n d T Aida, "Cyclic Ethers" in "Ring O p e n i n g P o l y m e r i s a t i o n " , Eds K J Ivin and T Saegusa, Vol. i, p 196, E l s e v i e r (1984) 13.5 0.9(m, 3); 1.5(m,4); 4.45(t,2); 5.52(s,2); Vma x 1632, 1282, 874 cm -I 14.Vma x (gas phase) 1755, 1665, 1281, 1225, 844 cm -I 15.Gc-ftir a n a l y s e s were p e r f o r m e d u s i n g an A c c u s p e c C o m p a c t II gc and Model 66 I.r. Interface in c o n j u n c t i o n with a N i c o l e t 5SX ftir spectrometer. Chromatograms were run on a 2 m x 3 m m i.d. g l a s s - l i n e d steel column p a c k e d with 10% OVl01 on Carbosorb. 16.Y Eirat and P H Plesch, J Polym. Sci. Polym. Lett., 13 135 (1975) * All nmr s a m p l e s were run as CDCI 3 solutions. Shifts are r e p o r t e d in p p m d o w n f i e l d from TMS (internal standard). ** All i.r. spectra were recorded as liquid films on KBr p l a t e s unless otherwise shown. A b s o r b a n c e s were strong unless o t h e r w i s e indicated (m/w) t Product m i x t u r e s c o n t a i n i n g b o t h h e m i f o r m a l nitrate and f o r m a t e esters, although o b t a i n e d in g o o d (50-70%) yields, d e c o m p o s e d within s e v e r a l hr, p r e c l u d i n g a c c u r a t e y i e l d measurements.

Copyright © Controller HMSO London 1989 (Received in UK 4 September 1989)