A full account is given of the chemical behavior observed for 7,
9
-dialkyladeninium salts (16). On treatment with boiling 1N aqueous NaOH for 60min, 16a,
b
,
d
,
e
(X=I), 16c (X=Br), and 16
f
(X=ClO
4) rearranged to isomeric
N6
, 7-dialkyladenines (21a-
f
) in 50-91% yields. Treatment of the salts with 0.
5
N aqueous
Na2CO3
at room temperature for 30-90min or with Amberlite CG-400 (OH
-) in H
2O at room temperature gave the ring-opened derivatives
22
a-
f
(in the trans-formamide form) in 56-
83
% yields, and rate constants for the ring-opening reactions of 16a,
b
,
d
-g (X=ClO
4) and 16c (X=Br) leading to
22
a-g were determined in H
2O at pH
9
.
84
and ionic strength 0.50 at 25°C. Cyclization of
22
a with NaH in AcNMe
2 at room temperature or with boiling 1N aqueous NaOH produced 21a in
84
% or 72% yield, respectively.In solution, the trans-formamides
22
seemed to transform slowly into the cis-formamides 23, attaining equilibria. The existence of such an equilibrium in
D2O
or Me
2SO-
d6
at 25°C or in H
2O at pH
9
.
84
and ionic strength 0.50 at 25°C was kinetically confirmed in the case of
22
a, and the mechanism of the rearrangement of 16 to 21 through
22
is discussed on the basis of the above kinetic results and Deslongchamps' theory of stereoelectronic control. On treatment with NaBH
4 in MeOH at room temperature, 16a (X=I) furnished the 7,
8
-dihydro derivative 28 (
84
% yield), which slowly decomposed in H
2O at 60°C to give
22
a in 49% yield.The 7,
9
-dialkyladeninium salts (16) were found to be obtainable from N'-alkoxy-1-alkyl-
5
-formamidoimidazole-4-carboxamidines (
9
) through an alternative synthetic route : Alkylations of
9
with alkyl halides in HCONMe
2 in the absence of base, followed by hydrogenolysis of the N'-alkoxy group and cyclizatio (or vice versa) produced 16 in acceptable yields. In order to interpret the proton nuclear magnetic resonance spectrum of
22
a, the 2-deuterated species 26 was also synthesized from 24 via 25 and 27.
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