Organic Syntheses Procedure

^
Top

Org. Synth. 1998, 75, 215

DOI: 10.15227/orgsyn.075.0215

N-VINYLPYRROLIDIN-2-ONE AS A 3-AMINOPROPYL CARBANION EQUIVALENT IN THE SYNTHESIS OF SUBSTITUTED 1-PYRROLINES: 2-PHENYL-1-PYRROLINE

[ 2H-Pyrrole, 3,4-dihydro-5-phenyl- ]

Submitted by Kirk L. Sorgi, Cynthia A. Maryanoff, David F. McComsey, and Bruce E. Maryanoff¹ .

Checked by Christopher Deur and Louis S. Hegedus.

1. Procedure

A. 3-Benzoyl-N-vinylpyrrolidin-2-one . A dry, 2-L, three-necked, round-bottomed flask, equipped with a mechanical stirrer, addition funnel, heating mantle, and reflux condenser, is charged with 26.7 g (0.665 mol) of 60% sodium hydride (NaH, (Note 1)) and 250 mL of dry toluene (Note 2). The stirred suspension is heated at reflux while a mixture of 55.0 g (0.50 mol) of freshly distilled N-vinylpyrrolidin-2-one (Note 3) and 75.0 g (0.50 mol) of ethyl benzoate (Note 4) is slowly added (Note 5). Heating is continued for 10 hr (Note 6). The reaction mixture is cooled to room temperature and the resultant thick slurry is carefully diluted with 250 mL of saturated, aqueous ammonium chloride . The layers are separated and the aqueous layer is extracted again with 250 mL of toluene . The combined organic layers are dried (MgSO₄) and concentrated under reduced pressure to afford 108 g (>100%) of crude keto lactam product as an amber oil that may solidify on standing (Note 7).

B. 2-Phenyl-1-pyrroline . A 2-L, three-necked, round-bottomed flask, equipped with a mechanical stirrer, addition funnel, heating mantle, reflux condenser, and a short-path distilling head, is charged with 0.5 L of 6 N hydrochloric acid and heated at reflux; 100 g (0.46 mol) of crude keto lactam is dissolved in 62.5 mL of tetrahydrofuran (THF) and the solution is slowly added, over 1.5-2 hr. Tetrahydrofuran is collected during the addition by use of the short-path distilling head (Note 8). Following the addition, the distilling head is removed and the solution is heated at reflux for 4 hr, cooled to room temperature, filtered through a plug of glass wool, cooled to 0°C, made basic to pH 12 by using aqueous 50% sodium hydroxide , and extracted with methylene chloride (3 × 100 mL). The combined organic layers are dried (MgSO₄) and concentrated under reduced pressure to afford 69.2 g of crude product as an amber oil. The residue is distilled at reduced pressure (1-3 mm) and the fraction boiling at 75-85°C is collected to afford 41.0 g (61% yield) of purified product as a clear, colorless oil that solidifies on standing (Note 9).

2. Notes

1. Sodium hydride was a 60% dispersion in mineral oil; 80% or 95% NaH can also be used.

2. Reagent grade toluene should be dried over 4 Å molecular sieves. Anhydrous tetrahydrofuran in SureSeal bottles from the Aldrich Chemical Company, Inc. , can also be used.

3. Higher yields are obtained when freshly distilled N-vinylpyrrolidin-2-one is used.

4. Ethyl benzoate was used as received from the Aldrich Chemical Company, Inc.

5. The addition rate is determined by the rate of hydrogen evolution. Hydrogen evolution ceases before addition of the mixture is complete.

6. A thick precipitate forms at this time.

7. The crude keto lactam is used without further purification. However, the crude solid can be crystallized from warm 2-propanol to yield 68 g of material (63%): mp 66.5-69.5°C; ¹H NMR (400 MHz, CDCl₃) δ: 2.13-2.37 (m, 1 H), 2.65-2.75 (m, 1 H), 3.42-3.58 (m, 1 H), 3.58-3.74 (m, 1 H), 4.31-4.51 (m, 2 H), 4.57 (dd, 1 H, J = 9.4, 5.2), 7.01 (dd, 1 H, J = 15.9, 9.0, CH vinyl), 7.30-7.63 (m, 3 H), 7.64-7.47 (m, 2 H) ; IR (KBr) cm⁻¹: 1697, 1673, 1635, 1394, 1278, 816 ; MS (FAB) m/z 238 (M⁺ + Na), 216 (MH⁺), 105 .

8. This high-dilution technique minimizes polymerization. To avoid formation of the brown polymer, the addition must be slow. The submitters recommend adding the keto lactam/THF solution over 1.5-2.0 hr to a vigorously boiling solution of 6 N hydrochloric acid. This addition time leads to high yields of product with minor amounts of dark polymer. It is also important to prevent hydrochloric acid vapors from coming in contact with the keto lactam/THF solution while it is in the addition funnel. This can be accomplished by passing a slow stream of an inert gas over the solution from the top of the addition funnel or by using an addition funnel without a pressure equalizing arm.

9. This material, which yellows on standing, was >95% pure by GLC analysis (DB-5 capillary column, 110°C for 2 min, increase at 30°/min to 290°C). Overall yields should range from 70-75%. The physical properties of 2-phenyl-1-pyrroline are as follows: mp 41.5-44.0°C; ¹H NMR (CDCl₃, 90 MHz) δ: 1.70-2.10 (m, 2 H), 2.60-2.97 (m, 2 H), 3.80-4.13 (m, 2 H), 7.13-7.47 (m, 3 H), 7.56-7.93 (m, 2 H) ; ¹³C NMR (100 MHz, CDCl₃) δ: 22.41 (CH₂), 34.56 (CH₂), 61.34 (CH₂), 127.36 (CH), 128.12 (CH), 129.96 (CH), 134.40 (C), 172.69 (C=N) ; IR (CHCl₃) cm⁻¹: 3061, 2948, 2864, 1616, 1575, 1496, 1447, 1340, 1310, 1049, 991, 961 ; (EI, 70 ev) m/z 145 (M⁺), 117, 104, 89, 77, 63, 51 .

Handling and Disposal of Hazardous Chemicals

The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.

These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.

3. Discussion

This method for preparing 2-phenyl-1-pyrroline, and assorted 2-substituted 1-pyrrolines, is one of the best currently available, particularly because it reproducibly affords clean materials. Generally, the procedure is amenable to various aromatic esters;² ³ ⁴ it has also been applied successfully to aliphatic esters (Table I).⁵ An advantage of this method is the use of readily available, inexpensive N-vinyl-pyrrolidin-2-one as a key starting material. This compound serves effectively as a 3-aminopropyl carbanion equivalent. The method illustrated in this procedure has been extended to include the synthesis of 2,3-disubstituted pyrrolines. Thus, alkylation of the enolate of the intermediate keto lactam, followed by hydrolysis, leads to various disubstituted pyrrolines in good yields (see Table II).⁵

TABLE I
PREPARATION OF 2-ALKYL-1-PYRROLINES


Entry	Ester	1	Yield 1 (%)^a	2	Yield 2 (%)^b

1	PhCH₂CO₂Et		96 ^c		66
2	c-C₆H₁₁CO₂CH₃		99		73
3	CH₃(CH₂)₈CO₂CH₃		99		81
4	BnO(CH₂)₃CO₂CH₃		96		95 ^d
5	i-PrCO₂CH₃		99		98
6	t-BuCO₂CH₃		99		98

a) Crude yield. b) Isolated purified yield from N-vinylpyrrolidin-2-one. c) Two equiv of NaH were used.
d) Benzyl group was removed during the hydrolysis.

TABLE II
PREPARATION OF 2,3-DISUBSTITUTED-1-PYRROLINES


Entry	R	R'-X	3	Yield 3 (%)^a	4	Yield 4 (%)^b

1	Ph	PhCH₂Br		99 (70)		94 ^c
2	Ph	CH₃I		99		87
3	Ph	H₂C=CHCH₂Br		92		86
4	t-Bu	CH₃I		97		82
5	i-Pr	PhCH₂Br		99		77
5	i-Pr	CH₃I		77		51

a) Crude yield. Bracketed yield is after purification by crystallization. b) Isolated purified yield from 1.
c) Yield from purified 3.

Other methods are available for the synthesis of 2-substituted 1-pyrrolines. A comparison study of their preparation from organolithium reagents and N-vinyl-pyrrolidin-2-one has been reported.⁶ Additions of phenyllithium to N-acylpyrrolidin-2-one ⁷ and phenyl Grignard reagents to a methyl imidate derived from 2-pyrrolidinone ⁸ are also useful (although the latter process requires a strong methylating agent). Two Friedel-Crafts methods⁹ ¹⁰ ¹¹ and the reaction of aroyl chlorides with 2-pyrrolidinone ¹² have been described. There is also a useful procedure, similar to the one presented here, that employs N-trimethylsilylpyrrolidin-2-one.¹³ ¹⁴

2-Phenyl-1-pyrroline is useful for various purposes.¹⁵ ¹⁶^,¹⁷ In particular, its reduction product, 2-phenylpyrrolidine, is important in the synthesis of pyrroloisoquinoline antidepressants,⁴^,¹⁸ ¹⁹ ²⁰ and can be a starting point in alkaloid synthesis.²¹ ²² The overall reaction sequence described here has been used to prepare nicotine derivatives such as myosmine.²^,³

References and Notes

The R. W. Johnson Pharmaceutical Research Institute, Welsh & McKean Roads, Spring House, PA 19477.
Brandange, S.; Lindblom, L. Acta Chem. Scand. Ser. B 1976, 30, 93;
Jacob, P., III J. Org. Chem. 1982, 47, 4165;
Sorgi, K. L.; Maryanoff, C. A.; McComsey, D. F.; Graden, D. W.; Maryanoff, B. E. J. Am. Chem. Soc. 1990, 112, 3567.
Haslego, M. L.; Maryanoff, C. A.; Scott, L.; Sorgi, K. L. Heterocycles 1993, 35, 643.
Bielawski, J.; Brandange, S.; Lindblom, L. J. Heterocycl. Chem. 1978, 15, 97.
Giovannini, A.; Savoia, D.; Umani-Ronchi, A. J. Org. Chem. 1989, 54, 228.
Etienne, A.; Correia, Y. Bull. Soc. Chim. Fr. 1969, 3704.
Koller, W.; Schlack, P. Ber. 1963, 96, 93;
Cheng, S.-S.; Piantadosi, C.; Irvin, J. L. J. Med. Chem. 1966, 9, 945;
Cheng, S.-S., Piantadosi, C.; Irvin, J. L. J. Pharm. Sci. 1968, 57, 1910.
Mundy, B. P.; Larsen, B. R.; McKenzie, L. F.; Braden, G. J. Org. Chem. 1972, 37, 1635.
Hu, M. W.; Bondinell, W. E.; Hoffmann, D. J. Label. Compounds 1974, 10, 79;
Seeman, J. I.; Secor, H. V.; Armstrong, D. W.; Timmons, K. D.; Ward, T. J. Anal. Chem. 1988, 60, 2120.
Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 8952;
Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 11703.
Mariano, P. S. Tetrahedron 1983, 39, 3845; Mariano, P. S. Acc. Chem. Res. 1983, 16, 130.
Maryanoff, B. E.; McComsey, D. F.; Gardocki, J. F.; Shank, R. P.; Costanzo, M. J.; Nortey, S. O.; Schneider, C. R.; Setler, P. E. J. Med. Chem. 1987, 30, 1433;
Maryanoff, B. E.; Shank, R. P.; Gardocki, J. F. Drugs of the Future 1986, 11, 18;
Maryanoff, B. E.; McComsey, D. F. J. Heterocycl. Chem. 1985, 22, 911.
For reviews, see: (a) Ikeda, M.; Sato, T.; Ishibashi, H. Heterocycles 1988, 27, 1465;
Rajeswari, S.; Chandrasekharan, S.; Govindachari, T. Heterocycles 1987, 25, 659.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

N-Vinyl-2-pyrrolin-2-one:
2-Pyrrolidinone, 1-vinyl-; 2-Pyrrolidinone, 1-ethenyl- (9); (88-12-0)

2-Phenyl-1-pyrroline:
1-Pyrroline, 2-phenyl- (8);
2H-Pyrrole, 3,4-dihydro-5-phenyl- (9); (700-91-4)

3-Benzoyl-N-vinylpyrrolidin-2-one:
2-Pyrrolidinone, 3-benzoyl-1-ethenyl-, (±)- (12); (125330-80-5)

Sodium hydride (8,9); (7646-69-7)

Ethyl benzoate:
Benzoic acid, ethyl ester (8,9); (93-89-0)

Notes

References/EndNotes

Article Compounds

Authors