[5176-27-2]  · C9H13NO2  · N-(t-Butoxycarbonyl)pyrrole  · (MW 167.21)

(used as a synthetic equivalent of pyrrole; the t-butoxycarbonyl group can be cleaved under acidic or basic conditions1)

Physical Data: bp 98-99 °C/19 mmHg.

Solubility: freely sol common organic solvents.

Analysis of Reagent Purity: 1H NMR.

Preparative Method: see Reese and Dhanak.1

Purification: distillation under reduced pressure.

N-(t-Butoxycarbonyl)pyrrole is prepared by the deprotonation of pyrrole with Sodium Hydride followed by acylation with phenyl t-butyl carbonate.1 Other preparative methods include the acylation of pyrrole with Di-t-butyl Dicarbonate in the presence of Triethylamine and catalytic 4-Dimethylaminopyridine,2 and treatment of the potassium salt of pyrrole with t-Butyl Azidoformate.3

N-(t-Butoxycarbonyl)pyrrole serves as a convenient synthetic equivalent of pyrrole. Many of the synthetically important transformations of pyrrole, substituted pyrroles, and indoles involve strongly basic conditions and it is often necessary to protect the nitrogen. The t-butoxycarbonyl group can be attached and removed under mild conditions and is also stable to a variety of conditions used for functionalization of the pyrrole ring. Thus 2-lithio-N-(t-butoxycarbonyl)pyrrole can be generated quantitatively with Lithium 2,2,6,6-Tetramethylpiperidide and trapped with Chlorotrimethylsilane or other electrophiles. The protecting group can be subsequently removed using a solution of Sodium Methoxide in methanol (eq 1).4 Under these conditions, (1-hydroxy)alkylpyrroles (derived from the addition of the 2-lithiopyrrole to aldehydes) are converted to (1-methoxy)alkylpyrroles. The t-butoxycarbonyl group can also be cleaved under acidic conditions using Trifluoroacetic Acid in CH2Cl2.1,2

N-(t-Butoxycarbonyl)pyrrole also undergoes Diels-Alder reactions with acetylene, benzyne, and their derivatives. Thus reaction of N-(t-butoxycarbonyl)pyrrole with benzyne generated from bromofluorobenzene and magnesium gave the adduct in 41% yield (eq 2).3

Other alternatives to N-(t-butoxycarbonyl)pyrrole that can be used for some of the reactions described above include various N-trialkylsilylpyrroles1,5 and methoxycarbonylpyrrole.6

1. Dhanak, D.; Reese, C. B. JCS(P1) 1986, 2181.
2. Grehn, L.; Ragnarsson, U. AG(E) 1984, 23, 296.
3. Carpino, L. A.; Barr, D. E. JOC 1966, 31, 764.
4. Hasan, I.; Marinelli, E. R.; Lin, L.-C. C.; Fowler, F. W.; Levy, A. B. JOC 1981, 46, 157.
5. Anderson, P. S.; Christy, M. E.; Engelhardt, E. L.; Lundell, G. F.; Ponticello, G. S. JHC 1977, 14, 213.
6. Swenton, J. S.; Oberdier, J.; Rosso, P. D. JOC 1974, 39, 1038.

William H. Pearson & P. Sivaramakrishnan Ramamoorthy

The University of Michigan, Ann Arbor, MI, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.