[116360-40-8]  · C20H35NSn  · N-[(Tri-n-butylstannyl)methyl]benzaldimine  · (MW 408.27)

(synthesis of 2-phenylpyrrolidines by [3 + 2] cycloaddition of the derived 2-azaallyl anion with alkenes;1,2 related compounds allow synthesis of other 2-substituted, 2,2-disubstituted, 2,5-disubstituted, or 2,2,5-trisubstituted pyrrolidines or pyrrolines1-3)

Physical Data: bp 145-155 °C/0.1 mmHg (Kugelrohr air bath).

Solubility: freely sol common organic solvents.

Form Supplied in: clear, colorless oil; not available commercially.

Analysis of Reagent Purity: 1H NMR.

Preparative Methods: prepared by Staudinger reaction between benzaldehyde, Triphenylphosphine, and (azidomethyl)tributylstannane [prepared from (iodomethyl)tributylstannane and Sodium Azide].2 A more convenient procedure for the preparation of similar stannanes by condensation of an aldehyde or ketone with (aminomethyl)tributylstannane has been developed.3 Related 2-azaallylstannanes such as 1-alkyl-, 1,1-dialkyl-, 1,3-dialkyl-, and 1,1,3-trialkyl-2-azaallylstannanes may also be prepared, particularly using the latter method.

Handling, Storage, and Precautions: since tetraalkylstannanes in general are considered toxic,4 handling in a fume hood is recommended. The reagent is stable in a freezer for extended periods, but is easily hydrolyzed by aqueous acids, and is partially hydrolyzed by silica gel chromatography.

Synthesis of 2-Phenylpyrrolidines.

Treatment of N-[(tributylstannyl)methyl]benzaldimine with n-Butyllithium in the presence of stilbene produces 2,3,4-triphenylpyrrolidine in good yield (eq 1).1,2 The reaction proceeds by transmetalation to produce a 2-azaallyl anion, which undergoes a [p4s + p2s] cycloaddition with stilbene, generating an N-lithiopyrrolidine. Quenching the reaction with water or other electrophiles allows the introduction of a variety of N-substitutents. The anionophile must be present during the transmetalation, since the 2-azaallyl anions have a limited lifetime under these conditions. The best anionophiles are those that are relatively stable to butyllithium at low temperature, and are relatively reactive due to the presence of substituents which may stabilize negative charge build up. Successful examples include stilbene, styrene, a-methylstyrene, diphenylacetylene, phenyl vinyl sulfide, phenyl vinyl selenide, and various vinylsilanes.1,2 More electron-deficient anionophiles such as acrylates are unsuccessful. Examples are shown in eq 2.2

Related Pyrrolidine Syntheses using 2-Azaallyl Anion Cycloadditions.

In addition to the synthesis of 2-arylpyrrolidines as shown above, the 2-azaallyl anion method is useful for the preparation of a variety of 2-alkylpyrrolidines.1,2 Similar restrictions regarding the anionophile apply. For example, vinyl selenides are excellent reaction partners (eq 3).2 The phenylseleno group may be reductively or oxidatively removed, producing simple pyrrolidines or pyrrolines (eq 4).2 Intramolecular examples are also known (eq 5).1,2 More recently, 2-azallyl anions bearing two or three alkyl groups have been generated and used in cycloadditions, leading to 2,2-disubstituted, 2,5-disubstituted, and 2,2,5-trisubstituted pyrrolidines.3 Example are shown in eqs 6 and 7. Note that 1,3-dialkyl-2-azaallyl anions produce pyrrolidines with a 2,5-cis-relationship, presumably due to the preferential formation of the W form of the anion (eq 7).

Related Methods for Pyrrolidine Synthesis.

Kaufmann has studied the formation and cycloaddition of 2-azaallyl anions derived from the deprotonation of imines such as N-benzylidenebenzylamine with amide bases.5 Only anions bearing two or more aryl groups may be used, unless the cycloaddition is intramolecular, where one aryl group on the anion is necessary.6 The generation of aryl-substituted 2-azaallyl anions by the desilylation of N-(trimethysilyl)methanimines has been reported.7,8 A variety of 2-azaallyl anions bearing strong electron-withdrawing groups have been generated and used in cycloaddition reactions.9 The lower reactivity of these anions necessitates the use of more reactive anionophiles such as acrylates. Azomethine ylides are closely related to 2-azaallyl anions, and have also been used to synthesize pyrrolidines by dipolar cycloadditions with alkenes.10 A review which compares the two methods has appeared.11

Related Reagents.


1. Pearson, W. H.; Szura, D. P.; Harter, W. G. TL 1988, 29, 761.
2. Pearson, W. H.; Szura, D. P.; Postich, M. J. JACS 1992, 114, 1329.
3. Pearson, W. H.; Postich, M. J. JOC 1992, 57, 6354.
4. Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in Organic Synthesis; Butterworths: London, 1987.
5. Kaufmann, T. AG(E) 1974, 13, 627.
6. Pearson, W. H.; Walters, M. A.; Oswell, K. D. JACS 1986, 108, 2769.
7. (a) Imai, N.; Achiwa, K. CPB 1987, 35, 2646. (b) Achiwa, K.; Imai, N.; Inaoka, T.; Sekiya, M. CPB 1984, 32, 2878.
8. Tsuge, O.; Kanemasa, S.; Yamada, T.; Matsuda, K. JOC 1987, 52, 2523, and references cited therein.
9. Kanemasa, S.; Tsuge, O. In Advances in Cycloaddition; Curran, D. P., Ed.; JAI: Greenwich, CT, 1993; Vol. 3, pp 99-159.
10. (a) Padwa, A. In Advances in Cycloaddition; Curran, D. P., Ed.; JAI: Greenwich, CT, 1990; Vol. 2, Chapter 1. (b) Tsuge, O.; Kanemasa, S. Adv. Heterocycl. Chem. 1989, 45, 231. (c) Vedejs, E. In Advances in Cycloaddition; Curran, D. P., Ed.; JAI: Greenwich, CT, 1988; Vol. 1, pp 33-51.
11. Pearson, W. H. In Studies in Natural Products Chemistry; Atta-ur-Rahman, Ed.; Elsevier: Amsterdam, 1988; Vol. 1, pp 323-358.

William H. Pearson & P. Sivaramakrishnan Ramamoorthy

University of Michigan, Ann Arbor, MI, USA

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