The synthesis of some novel benzo-crown ethers by =-amidomethylation is described.
~-Amidomethylation at carbon (the Chernyak-Einhorn reaction) has been the subject of numerous articles and reviews [2, 3], but there have been no reports of the use of benzocrown ethers in such reactions, and only a few examples of the use of PPA as catalyst [6,5]. It is, however, known that PPA is an excellent solvent and catalyst in the alkylation [6,7] and acylation [8] of benzo-crown ethers.
We have now shown that benzo-crown ethers undergo efficient =-amidomethylation on treatment with N-hydroxymethylphthalimide and N-hydroxymethylamides in PPA.
Examination of molecular models shows that it is only possible to introduce two amidomethyl substituents into the aromatic ring in henzo-crown ethers, in positions 4 and 5. This was confirmed by the observation that amidomethylation of dibenzo-18-crown-6 (I) and dibenzo-24-crown-8 (II) with two equivalents of N-hydroxymethylphthalimide gave a mixture of the unsubstituted crown ether together with mono-, di-, and trisubstituted products. Using a crown ether-~lectrophile reagent ratio of 1:4 at 100~ high yields of the tetraphthalimido-compounds (III) and (IV). Under similar conditions, benzo-15-crown-5 gave the diphthalimidocompound (VI). The use of the more reactive N-chloromethy!phthalimide as the electrophile enabled the reaction temperature to be reduced to 70~
Attempts to carry out the reaction in concentrated sulfuric acid were unsuccessful, apparently as a result of hydrolysis of the ether linkages in the macrocycle. I J ~O O" ~'~i-phil---"/" ">~" "O O/~'~ "~--~rPht I, II .0" \ I. |II IL=I: IL IV n=2 X=OH, C1 Z PhtNCH2X PPA PhI=o-C=lla(CO) 2
In.
Vl
Reaction of N-hydroxymethylphthalimide with the crown ether (I) gave the tetraamidomethyl compound (VII), and N-hydroxymethylbenzamide or bis-N-benzamidomethyl ether with crown ethers (I) and (V) afforded compounds (VIII) and (IX).
It was found that under similar conditions N-hydroxymethyl-p-toluenesulfonamide and Nhydrcxymethyi-N-methyl-p-toluenesulfonamide eliminated CH20 at temperatures as low as 30-40~ this then undergoing polycondensation with the benzo-crown ether to give polymeric materials. *For Con~nunication 26, see [i].