We have studied the reaction of 1-vinyl-2-(2.furyl). and -(2-thienyl)pyrroles with trifluoroacetic anhydride, with hydrogen in the presence of catalysts (Raney nickel, palladium black, palladous chloride), with propargyl alcohol in electrophUic conditions [catalysis by perfluorobutyric acid in the system azoisobutyrodinitrile (AIBN)-CCI 4), and with alkane thiols with AIBN initiation. The products are novel substituted hetwylpyrroles.
The development and successful use of the Trofimov and related reactions [1, 2] applied to furan and thiophene oximes has led to the synthesis of a series of 1-vinyl-2-(2-furyl)-and -(2-thienyl)pyrroles [2, 3]. These compounds are interesting in terms of the comparative reactivity of both heterocycles and the effect of the heterocycle on the course of reactions of 1-vinylpyrroles [2] via the electronic interaction of beteroatoms and vinyl group.
Our study of the trifluoroacetylation of 1-vinyl-(2-furyl)-and -(2-thienyl)pyrroles [4] has been extended to novel compounds in the series with 3-alkyl substitucnts.
Trifluoroacetylation of 1-vinyl-2-(2-thienyl)-3-alkylpyrroles II and III gave only the a-substitution products VIII and IX, respectively. In contrast to 1-vinyl-2-(2-furyl)-pyrrole [4], attack of the furylpyrrole I by the trifluoroacetyl cation is directed principally toward the pyrrole ring. The structurally isomeric trifluoroacetyl pyrroles VI and VII are formed in approximately 35 and 27% yields, respectively. As in [4], and in contrast to [5], the products of simultaneous bis(trifluoroacetylation) on both heterocycles was not observed. Exchange of the vinyl group on the nitrogen atom for ethyl (pyrrole IV) does not change the usual direction of trifluoroacetylation [2]. This is also retained in the presence of a rather bulky group (triethyisilyiethyl), although it is known [6] that the route of electrophilic attack on the pyrrole can be changed by such substituents.
~COCF 3
C5115 N/'~-'t2 0 ~.