B u l l . SOC. C h i m . Be lg . vo1.88/no 1-2/1979

PRODUCTS FROM THE ELECTROCHEMICAL REDUCTION OF AN N,N'-DISUBSTITUTED DIHYDROOIAZEPINIUM SALT.

by Douglas L loyd , C o l i n A . Vincent and David J . Walton Department o f Chemistry, Pu rd ie B u i l d i n g , U n i v e r s i t y o f St.Andrews,

St.Andrews, F i v e

and Jean-Paul Oeclercq, Gabr ie l Germain and Maur ice Van Meerssche, Labora to i re de Chimie physique e t de C r i s t a l l o g r a p h i e , Bat iment

L a v o i s i e r , U n i v e r s i t e de Louvain, 1, p lace Lou is Pasteur, 1348-Louvain-la-Neuve, Belgium.

Received 5 / 0 4 / 7 9 -b Accepted 6 / 0 4 / 7 9

E l e c t r o l y t i c r e d u c t i o n o f the 6-phenyl-2,3-dihydro-1,4-diazepinium c a t i o n ( I , R' = R' = H)

o r o f i t s mono-N-alkyl d e r i v a t i v e s ( e . g . I, R'=H, R 4 =Me) i n dimethyl formamide a t e i t h e r a mercury o r a p la t i num e lec t rode s u r p r i s i n g l y gave as produc ts 4,5-pyrrolotetrahydrodiazepines, w h s e fo rma t ion probab ly i nvo l ves d i m e r i s a t i o n o f an i n i t i a l l y formed r a d i c a l f o l l owed b y i n t ramo lecu la r displacement o f e thy lened iamine (lY2),

I I 1 1 1 1

Such a r e a c t i o n i n n o t p o s s i b l e i f bo th n i t r o g e n atoms a re s u b s t i t u t e d . An e l e c t r o l y t i c

reduc t i on under s im i 1 a r cond i t i ons o f 1,4-dibenzyl-6-phenyl-2,3-di hydro- l ,4-diazepinium pe r - ch lo ra te ( I , R' = R 4 = PhCH2) p rov ides th ree produc ts , namely the meso and racemic isomers o f

t he dimer (11, R = PhCH2), and another unexpected rearrangement p roduc t , t h e d i - i m i d a z o l i d i - ny lbu tad iene (111, R = PhCH2), i n a t o t a l y i e l d of 85-90%, t h e r a t i o o f t h e produc ts depen- d ing on cond i t i ons ( 3 ) . The s t r u c t u r e s o f these compounds have been proved by X-ray c r y s t a l l o - g raph ic ana lys i s (3 ) and spec t roscop ic da ta (mass spec t ra , n.m.r., i . r . ) a re i n accord. The

X-ray c r y s t a l l o g r a p h i c i n v e s t i g a t i o n o f t h e di-imidazolidinylbutadiene showed t h a t t he c rys - t a l s examined cons is ted o f t h e geomet r ic isomer (111), b u t 13C-n.m.r. spec t ra o f an o v e r a l l

sample o f t h i s p roduc t i n d i c a t e d t h a t i t was a m i x t u r e o f more thanone geomet r ic isomer s i n c e

there were two d i s t i n c t s i g n a l s a t t r i b u t a b l e t o 2 - i m i d a z o l i d i n y l carbon atoms and two s i g n a l s a t t r i b u t a b l e t o benzy l methylene carbon atoms.

Produc t ion o f t he b i s te t rahyd rod iazep ines (11) accords w i t h t h e o r i g i n a l l y suggested r e - duc t i on pa th f o r d ihydrod iazep in ium s a l t s ( l ) . I t remains t o be proved whether convers ion o f t he seven-membered r i n g s i n t o the five-membered r i n g s o f (111) precedes o r f o l l o w s d imer isa- t i o n ; i n e i t h e r case one p o s s i b l e mechanism invo lves a re t ro -M ichae l type o f r e a c t i o n b r i n - g ing about r ing-open ing , f o l l owed by r i n g - c l o s u r e o f t he r e s u l t i n g f r e e amine group on to an im ine carbon atom.

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Whereas solutions o f the pyrrolodiazepines produced by reduction of N-mono- or un-substi- tuted dihydrodiazepinium salts showed reversible changes on addition o f acid, addition o f di- lute aqueous acid to solutions o f either of the products from the presently described reduc- tion produces an irreversible change in their U.V. spectra.

REFERENCES

1. Lloyd, D., Vincent, C . A . , Walton, D.J., Declercq, J.P., Germain, G. and Van Meerssche, M. J.C.S. Chem. Corn., 1978, 499.

2. Declercq, J.P., Germain, G. & Van Meerssche, M.. Acta C r y s t . 1979, acceptedfor publication. 3. Details o f the electrolytic reduction (D.L., C.A.V. and D.J.W.) and X-ray analysis (J.P.D.,

G.G. and M.V.M.) will be published separately.

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