N. Mallesha et al. / Tetrahedron Letters 53 (2012) 641–645
645
Table 6
Wiley: New York, 2007; (c) Pearson, Anthony J.; William, R. Activating Agents
and Protecting Groups In Handbook of Reagents for Organic Synthesis; Wiley: New
York, 1999; (d) Kolienski, P. J. Protecting Groups, 3rd ed.; Thiems: Stuttgart,
2004.
Conversion of 1b–1a with different solvents
Entry
Solvent
Time (h)
Yield (%)
3. Bayerman, H. C.; Heiszwolf, G. J. J. Chem. Soc. 1963, 755.
1
2
3
4
5
Acetonitrile
MDC
Methanol
Ethyl acetate
THF
3
3
3
3
3
70
65
91
50
78
4. Bayerman, H. C.; Heiszwolf, G. J. Recl. Trav. Chem. Pays-Bas. 1965, 84, 203.
5. Bayerman, H. C.; Bontkoe, J. S. Proc. Chem. Soc. 1961, 249.
6. (a) Altschul, R. J. Am. Chem. Soc. 1948, 70, 2569; (b) Altschul, R. J. Am. Chem. Soc.
1946, 68, 2605.
7. Armstrong, A.; Brackenridge, I.; Richard, F. W.; Joanna, M. Tetrahedron. Lett.
1988, 29, 2483.
8. (a) Bartoli, G.; Bosco, M.; Locatelli, M. Org. Lett. 2005, 7, 427; (b) Bartoli, G. .;
Bosco, M.; Locatelli, M. J. Org. Chem. 2006, 71, 9580.
9. Alessandro, B.; Occhiato, E. G.; Cristina, P.; Dina, S.; Silvia, T.; Venturello, P.
Synlett 2010, 812.
10. Kochetkov, H. K.; Derevitskaya, V. A.; Klimov, E. M. Tetrahedron. Lett. 1969, 10,
4769.
11. Derevitskaya, V. A.; Klimov, E. M.; Kochetkov, H. K. Tetrahedron Lett. 1970, 11,
4269.
ambient condition. This method is useful for the preparation of tert-
butyl ethers and laboratory scale preparation of tert-butyl protec-
tion of amino acids under normal laboratory condition and also we
have developed a green protocol for the deprotection of tert-
butyl ether.
12. (a) Tauko, S. J. Chem. Eng. Jpn. 1982, 15, 249; (b) Kiss, J. J. Phy. Chem. A 2011, 115,
7180; (c) Liuha, K. Microporous Mesoporous Mater. 2010, 127, 90.
13. Procedure for the preparation of tert-butyl ethers: 10 mmol of substrate, 2 g of
molecular sieves and 10 mL of MTBE were taken in a 50 mL round bottom flask
fitted with septum and cooled to 25 °C. To this solution 20 mmol of sulfuric
acid was added very slowly using syringe. Reaction was carried out at 25 °C for
given reaction time as shown in Table 4. Reaction mass was slowly quenched
in to 20 mL of saturated aqueous solution of sodium bicarbonate. Organic layer
was separated and washed with water (2 Â 20 mL), dried over anhydrous
sodium sulphate. Unreacted MTBE was recovered and reused. Obtained residue
was purified by eluting through flash column using hexane and MTBE (10:1).
14. Procedure for the preparation of tert-butyl ether and esters of amino acids:
10 mmol of amino acid, 4 g of molecular sieves and 20 mL of MTBE was taken
in a 50 mL round bottom flask fitted with a septum and cooled to 25 °C. To this
solution 30 mmol of sulfuric acid was added very slowly using syringe.
Reaction was carried out at 25 °C for given reaction time as shown in Table 5.
Reaction was slowly quenched in to 25 mL of saturated aqueous solution of
sodium bicarbonate. Organic layer was separated, and aqueous layer was
extracted twice with hexane. Combined organic layer was washed with water,
dried over sodium sulphate and the solvent was removed by distillation.
15. Procedure for the deprotection of tert-butyl ether: Compound 1b (1 g) was
taken in 5 mL of methanol in a 50 mL round bottom flask and 1 g of amberlite
resin 120-H was added. Reaction mass was refluxed for 5 h, filtered and
washed with methanol. Methanol was removed under vacuum to yield pure
compound 1a.
Acknowledgments
The authors NM and SPR thank Mr. Chethan P. Joshi, Managing
Director and Mr. Jayesh P. Joshi, Director, CJEX Biochem for their
encouragement.
Supplementary data
Supplementary data associated with this article can be found, in
References and notes
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