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Regioselective Synthesis of6H-Pyrano[3,2-d]pyrimidine-2,4(1H)-diones andFuro[3,2-d]pyrimidine-2,4(1H)-diones

 

作者: Krishna C. Majumdar,  

 

期刊: Journal of Chemical Research, Synopses  (RSC Available online 1997)
卷期: Volume 0, issue 9  

页码: 309-309

 

ISSN:0308-2342

 

年代: 1997

 

DOI:10.1039/a700009j

 

出版商: RSC

 

数据来源: RSC

 

摘要:

N N O HO O Me Me R2 X R1 + N N O O O Me Me R2 R1 1 2 3 R2 Br Br Cl Cl H H CH2OH CH2Cl H Me H H a b c d 2,3 X R1 i N N O O O Me Me R2 R1 3a–d N N O O Me Me O R1 R2 N N O O Me Me O 4a–d 5a–c R2 R1 i ii J. CHEM. RESEARCH (S), 1997 309 J. Chem. Research (S), 1997, 309 J. Chem. Research (M), 1997, 2062–2067 Regioselective Synthesis of 6H-Pyrano[3,2-d]pyrimidine- 2,4(1H)-diones and Furo[3,2-d]pyrimidine-2,4(1H)-diones Krishna C. Majumdar* and Udayan Das Department of Chemistry, University of Kalyani, Kalyani 741235, W.B. India A number of 1,3-dimethyl-6H-pyrano[3,2-d]pyrimidine-2,4(1H)-diones (4a–d) and 1,3-dimethylfuro[3,2-d]pyrimidine- 2,4(1H)-diones (5a–c) have been regioselectively synthesised in 88–94% and 80–90% yields respectively from the thermal [3s,3s] sigmatropic rearrangement of 1,3-dimethyl-5-(prop-2-ynyloxy)uracils (3a–d). We have recently reported1 the regioselective synthesis of pyrano[2,3-c]coumarins from aryloxybut-2-ynyloxy coumarins. There we established that it is possible to cyclise regioselectively the intermediate allenyl enol from the [3s,3s] sigmatropic rearrangement of the propynyl ethers of 3-hydroxycoumarin exclusively either to furo[2,3-c]coumarin or pyrano[2,3-c]coumarin simply by manipulating the reaction conditions.Literature reports2 revealed that Otter et al. studied the Claisen rearrangement of 5-(prop-2-ynyloxy)- uracil under a variety of conditions. Although they succeeded in obtaining a mixture of varying proportions of furo[3,2-d]- pyrimidine-2,4-dione and 6H-pyrano[3,2-d]pyrimidine- 2,4-dione they failed to isolate exclusively either of the products.This prompted us to undertake a study based on our recent experiences with subsequent cyclisation of the o-allenyl enol.3 Here we report the results of this investigation. The starting materials, 1,3-dimethyl-5-(prop-2-ynyloxy)- uracils (3a–d) were prepared in 88–94% yields by the alkylation of 1,3-dimethyl-5-hydroxyuracil4 1 with various prop- 2-ynylic halides (2a–d) in refluxing acetone in the presence of anhydrous potassium carbonate (Scheme 1).The 1,3-dimethyl-5-(prop-2-ynyloxy)uracil 3a was refluxed in purified chlorobenzene (bp 132 °C) to give 1,3-dimethyl- 6H-pyrano[3,2-d]pyrimidine-2,4(1H)-dione 4a as a white crystalline solid (88% yield), mp 202 °C. Other substrates (3b–d) were also similarly treated to furnish products (4b–d) in 90–94% yields (Scheme 2). The exclusive formation of products 4a–d from the ethers 3a–d is explicable4 by a [3s,3s] sigmatropic shift of the propynyl vinyl ether moiety of substrates 3a–d followed by enolisation, a 1,5-H shift and electrocyclic ring closure to give 4a–d.The ethers 3a–d were also heated in basic solvents, e.g., N,N-diethylaniline at 115 °C for 1.5 h to give exclusively the furo[3,2-d]pyrimidine-2,4(1H)-diones (5a–c) in 80–90% yields (Scheme 2). This conversion may also be completed in boiling pyridine (1.5 h).Substrates 3d showed a tendency to decompose when heated in N,N-diethylaniline and no tractable product could be obtained. A mixture of products 4 and 5 was obtained when the reaction was conducted in chlorobenzene in the presence of a small amount of N,N-diethylaniline. The ethers decomposed completely when heated in chlorobenzene in the presence of toluene-4-sulfonic acid. The formation of product 4 was unaffected when a radical initiator, azoisobutyronitrile (AlBN), was added to the reaction mixture.Only the one example each of the furo[3,2-d]pyrimidinedione 5a and the 6H-pyrano[3,2-d]pyrimidinedione 4a in a mixture of varying amounts was reported earlier by Otter et al.,2 the maximum yields reported for the compounds from different experiments being only 49% for 4a and 66% for 5a. The simple reaction conditions reported here seem to be general, as a number of furo- and pyrano-pyrimidines have been synthesised regioselectively in excellent yields, in each case exclusively one product being obtained.In addition the dimer of 4a reported by Otter et al. was not detected in the reaction mixture. We thank the CSIR (New Delhi) for financial assistance. One of us (U. D.) is grateful to U.G.C. (New Delhi) for a fellowship. Techniques used: UV, IR, 1H NMR, mass spectrometry References: 5 Schemes: 2 Received, 2nd January 1997; Accepted, 3rd June 1997 Paper E/7/00009J References 1 (a) K. C. Majumdar, R. N. De, A. T. Khan, S. K. Chattopadhyay, K. Dey and A. Patra, J. Chem. Soc., Chem. Commun., 1988, 777; (b) K. C. Majumdar and R. N. De, J. Chem. Soc., Perkin Trans. 1, 1989, 1901. 2 B. A. Otter, S. S. Saluja and J. J. Fox, J. Org. Chem., 1972, 37, 2858. 3 (a) K. C. Majumdar, A. T. Khan and R. N. De, Synth. Commun., 1988, 18, 1589; (b) K. C. Majumdar, D. P. Das and A. T. Khan, Synth. Commun., 1988, 18, 2027; (c) K. C. Majumdar, P. K. Choudhury and A. T. Khan, Synth. Commun., 1989, 19, 3249. 4 J. Zsindely and H. Schmid, Helv. Chim. Acta, 1968, 51, 1510. *To receive any correspondence (e-mail: kcm@klyuniv.ernet.in). Scheme 1 Reagents and conditions: i, Me2CO–K2CO3, reflux Scheme 2 Reagents and conditions: i, PhCl, reflux; ii, PhNEt2, 115 °C

 



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