Tetrahedron Letters No.8, pp. 585-586, 1970. Pergamon Press. Printed in Great Britain.

Harjit Singh and Santakh %ngh

Department of Chemistry, Panjab University, Chandigarh, India

(Received in I.K 5 January 1970; accepted for publication 16 January 1970)

The amino ketones formed on treatment of<-halocarbonyl compounds with thioureas or

cyclic systems where the ring N attached to the carbon carrying the thio function bears a

mobile H present an interesting amino ketone-carbinolamine tautomerism (1,2). Conclusive

evidences supported by 1.K.) N.d.K. data and chemical studies (3) have been presented in

favour of the entire existence of the amino ketone tautomer (I) when R = aryl and for the

predominance of carbinolamine tsutomer viz. hydroxy thiazolidine (II) when H = H, alkyl in

case of 2-thiobensa~midazolyl deri\ratives.

found that the existence of carbinolnmine

ring ;o be formed and that it exists o?ly

rings. tihereas if the formation of hi$er

strlct~~re prevails.

luring our study on swh compounds we have

tautorsers, is also dependent upon the size of the

when it involves the formation of five member:4

membered rin::s is required. the amino ketone

-Nj4 o=C;-R

’ R I

OH

585

586 No.8

(III) (a, n = 0, m = 2); (C, n = 1, " = 1); (L, n = 1, m = 2) where tie existence of cbrbiool-

amine tautomers re,quir-_s the formatiw of six membered or seven membered rlnys were pre!_fir>r!

by the condensation of 2-mercapto benzimidazole withp-chloro buta,lo?e-2 aid Z-~wcaptom2t!3yi3

benzimidazole witha-chloro acetone andp-chloro hiitanone-3 respectively in aqueo s sodium

nydroxide solutions at room temperature. dhereas III.4 (n = 0, m = i) exists as hydroxy

thiazolidine struc?.!lre (31, the amino ketone structure for IlIE. C and i? were attested b!- their

following spectral data : LIlti&“,~ 3425. 1695 cm-? (-Nti, C = 0);62.22 (s$d3),&3.13

(t, J = 7Hz,-CH2),d4.6 (t, J= 71+2,-CH2),67.2-7.6 (m, aromatic protons). IIlC,vk%385,

1695 cm-1 (NH, C =0),62.25 (s, cd3J.43.36 (s, CH;),63.95 (5, -bi2),67.%7.5 im. arowtic

Likewise,IVA (n = 1) existed as hydroxy thiasolidine derivative (&+a~ 3373, 1'25 cm-l, tertisry Kw2.

-OH) (4) and IVb (n = 2) favoured the amino ketone structure wwal3i20, 1710 cm-l, -,in and

- c == 0).

Chemical evidence to these tautomeric structures is fllmished oy toe <act that whey

capable of existence as carbilol amiws bhey undergo facile d-:oydrations, c '%?racte_ristiL: of

tertiary alcohols, whereas otherwise tney require sow:.hat drastic conditions i'inpublished).

Conversely, these results can predict the conditions for such cyclodehydration-:.

Acknowledgements :- Ihn authors thank Lr T . G.S, sidhu for h?lp in outaislinz the N.PJ.3. soerr,-a

and the U.G.::. for finaric1al assistance.

1.

2.

3.

4.

5.

References

G.Bike in "ddr~ances in detsrocyclic Chetistry", Vol.1, Ed., A.Y. katritzky, A-a,!elnic

Press, Inc., N.Y. 1963, F. 167.

B,Stanovnik, b.Tisler and A.Vrbanic. J_Org.Chem., 3b, 996113691 and ref:r+nces therein. -