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Synthesis 2010(7): 1209-1216  
DOI: 10.1055/s-0029-1218670
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Reactions of 2-Methyl- and 1,2-Dimethyl-1,4,5,6-tetrahydropyrimidine with Aroyl Chlorides: Diverse Reactivities of Cyclic Ketene N,N′-Acetals Generated in situ

Guozhong Yea, Sabornie Chatterjeea, Aihua Zhoub, Bobby Lloyd Barkera, Chunlong Chenc, Yingquan Songa, Charles U. Pittman Jr.*a
a Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, USA
b Pharmacy School, University of Wisconsin-Madison, WI 53706, USA
c Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
Fax: +1(662)3257611; e-Mail: cpittman@chemistry.msstate.edu;
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Publication History

Received 6 November 2009
Publication Date:
05 February 2010 (online)

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Abstract

2-Methyl-1,4,5,6-tetrahydropyrimidine reacted with two equivalents of aroyl chloride in tetrahydrofuran-triethylamine to give N,N′-diaroyl cyclic ketene N,N-acetals that are inert to excess aroyl chlorides. No carbon-carbon bond was formed in these reactions. Conversely, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine reacted with three equivalents of aroyl chloride under the same conditions to give N-aroyl N′-methyl β,β-dioxo cyclic ketene N,N′-acetals, with formation of two carbon-carbon bonds. Various reactions of cyclic amidines with aroyl chlorides were observed and are discussed in terms of the effects of the ring size and substituents on the reactivities of the cyclic ketene N,N′-acetals generated in situ.

Key words

acetals - aroyl chlorides - cyclic amidines - pyrimidines