Synthesis and X‐Ray Crystal Structures of Novel Spiro 1,3‐Benzoxazine Dimers.

Abstract

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Synthesis and X-ray Crystal Structures of Novel Spiro 1,3-benzoxazine Dimers

“…The 1 H NMR spectrum of 3a displayed a three-proton singlet at δ 1.99 ppm for the methyl group and two one-proton doublets at δ 3.38 and 3.58 ppm with J = 11 Hz for the non-equivalent protons of the methylene group, besides signals for the aromatic protons. The noise-decoupled 13 C NMR spectrum of 3a showed the expected 26 signals. Four aliphatic signals appeared at δ 32.16, 59.71, 65.50 and 85.35 ppm which are assigned to the methyl and methylene groups, position 10'b, and the spiro carbon atom, respectively.…”

“…[1][2][3][4][5][6] Recently we have been able to obtain spiro-quinazoline dimers from the reaction of 2-aminoacetophenone hydrazones with triphosgene. 13 Hydrazones of 2-hydroxyacetophenone which carry a chlorine or bromine substituent gave 1,3benzoxazines upon treatment with triphosgene. 14 In the present work we report the synthesis of spiro-1,3-benzoxazine dimers in two steps from 2-hydroxyacetophenones.…”

Isolation and synthesis of cryptosanguinolentine (isocryptolepine), a naturally-occurring bioactive indoloquinoline alkaloid

“…88 In that direction, in 2017 Aksenov et al conjectured that PPA could promote a one pot synthesis of the intermediate hydrazone 70 required 89 for Fischer indolization (Scheme 14), as well as drive to completion the formation of the indole moiety (71), and also participate in the subsequent intramolecular Vilsmeier reaction between an aromatic amine and a carboxylic acid, for the nal cyclization leading to isocryptolepine (7). 90 However, PPA failed to promote the synthesis of the hydrazone between ortho-aminoacetophenone (39) and phenylhydrazine (38), favoring self-condensation of the ketone, and this step had to be performed in EtOH under formic acid catalysis 91 or even better, under solventless conditions, for 10 min at 120 C. Furthermore, despite PPA was able to promote the Vilsmeier cyclization with various carboxylic acids, but formic acid proved to be unstable to the reaction conditions, decomposing into CO and CO 2 and furnishing 7 in only 25% yield. 92 Therefore, a formic acid surrogate was sought and triazine was proposed to fulll this place.…”