Facile and Selective O-Alkyl Transesterification of Primary Carbamates with Titanium(IV) Alkoxides

Journal of Organic Chemistry

Volumn 62, Issue 21, 1997, Pages 7096-7097

  Shapiro, Gideon ^a   Marzi, Martin ^a  

^a NOVARTIS PHARMA AG   (Switzerland)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000022459     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo971498z     Document Type: Article

References (17)

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4. (b) Seebach, D.; Jaeschke, G.; Gottwald, K.; Matsuda, K.; Formisano, R.; Chaplin, D. A.; Breuning, M.; Bringmann, G. Tetrahedron 1997, 53, 7539.
5. Oppolzer, W.; Lienard, P. Helv. Chim. Acta 1992, 75, 2572.
6. Froneman, M.; Modro, T. A. Synthesis 1991, 201.
7. (a) Sakaitani, M.; Ohfune, Y. J. Org. Chem. 1990, 55, 870.
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9. (c) Sakaitani, M.; Ohfune, Y. Tetrahedron Lett. 1985, 5543.
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11. Roos, E. C.; Bernabe, P.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1995, 60, 1733.
12. Steglich, W.; Rehwinkel, H. Synthesis 1982, 826.
13. 4 is a highly insoluble species. When absolute methanol was used, the titanium salt precipitate formed slowly, but addition of 5% water accelerated the process dramatically.
14. This is consistent with the selectivity for carboxylic acid esters observed by Steglich using 0.25-0.5 equiv of titanium alkoxide in refluxing THF.
15. At higher temperatures the starting material began to disappear with the desired transesterification remaining undetected.
16. 4 in refluxing toluene twice with an excess, 3-4 equiv, of allyl alcohol with azeotropic removal of 2-propanol. For higher boiling alcohols such as benzyl alcohol, a slight excess of the alcohol is used with a single azeotropic removal of 2-propanol.
17. 1H NMR and MS characterization was performed for all compounds which were also independently prepared by standard procedures using the corresponding amine and an appropriate carbamoylating agent.