Untitled

Synthesis of 2-amino-4H-3,1-benzoxazines and 2-amino-4H-3,1-benzothiazines by the rearrangement of o-cyclopropylphenylureas and o-cyclopropylphenylthioureas

“…There has been considerably less work on the transformations of cyclopropane compounds, in which the substituents, not directly bound to the cyclopropane ring, participate in the reaction. Nevertheless, examples of such transformations [9,[12][13][14] show that the synthetic scope of functionally-substituted cyclopropanes may be considerably expanded. Here, definite promise is found in intramolecular acid-catalyzed ortho-substituted arylcyclopropanes due to the unique ortho-orienting effect of the cyclopropane substituent in electrophilic nitration reactions [15][16][17].…”

“…This hypothesis is supported, for example, by the finding that neither o-nitrophenylcyclopropanes nor o-cyanophenylcyclopropanes rearrange by the action of trifluoroacetic acid, while these compounds are converted quantitatively to the corresponding products of transformation of the three-membered carbocycle by the action of concentrated sulfuric acid [12,18]. It is interesting that phenylcyclopropane lacking electron-withdrawing substituents or phenylcyclopropanes with weak electron-withdrawing substituents in the ortho position [5,14,19] are converted by the action of trifluoroacetic acid, similarly to cyclopropylureas 2a-i, into the corresponding cyclopropane ring transformation products. _______ * Cyclopropane 2a was obtained by the reaction of 2-cyclopropylaniline (1) with potassium cyanate (see Experimental).…”

Cyclization of N-(2-cyclopent-1-en-1-ylphenyl)benzamides in solution and under mass-spectrometric conditions

“…It is known that carbocations of type A are also formed under conditions of mass spectrometry [3] (the direction of the conversion of the molecular ions and the structure of the resulting ions for the initial amides 3 and products 4 are considered by us below).…”

4H-3,1-benzoxazines from o-aminoacylbenzenes

“…As a consequence, only 3,1-benzoxazines with different substituents at C (2) were obtained. The very recently discovered rearrangement of 2-acylaminophenylcyclopropanes opens broader possibilities for the synthesis of substituted 4H-3,1-benzoxazines [7]. However, in this case, even with broad possibilities for varying the substituents both in the fused benzene ring and at C (2) in the 3,1-benzoxazine system, variation of substituents at C (4) of the heterocycle using this scheme is limited only to the most simple alkyl fragments.…”

“…In previous work [7], we have already noted that, in principle, we might expect the formation of 4H-3,1-benzoxazine products if there is a fragment in the starting aromatic substrate undergoing intramolecular acid-catalyzed heterocyclization, from which a benzylic carbenium site may be generated, while an NH-C(R)=O moiety is located in the ortho position to this fragment, permitting formation of a benzoxazine ring. In the present work, we have shown that substrates meeting these requirements may readily be synthesized from o-aminoacylbenzenes.…”