Studies on Ylides: Reactions of N-Pyridinium Phenancylides with «,/MJnsatiirated Ketones, I

Synthesis of 2,4,6-Triarylsubstituted Pyridines

Purshottam S. K endurkar and Ram S. T e w a r i Department of Chemistry, Harcourt Butler Technological Institute, Kanpur-2, India

(Z. Naturforsch. 29b. 552-555 [1974]; received January 17/April 16, 1974)

Ylide. N-pyridinium, Phenacylide, Ketones

Reactions of N-pyridinium phenancylides with different a, /8-unsaturated ketones give 2,4,6-triarylsubstituted pyridines, 2,6-diphenyl-4-(2-pyridyl) pyridines, 2-benzylidene-4,6- diphenyl pyridines and 2,4,6-triphenyl-3-bromopyridine. Ammonium acetate in acetic acid was used as cyclization agent. The structure of the products are supported by IR and NMR spectra.

Our interest in the reactivity of P- and As- studied the reactions of N-pyridinium phenancy­ ylides 1’2 towards carbonyl substrates prompted us lides with different a,/5-unsaturated ketones. to carry out studies on the reactivity of N-ylides with a,/?-unsaturated ketones. Results and Discussion Although K r o h n k e et al.3 have reported such N-pyridinium phenancylides (1 a-d) reacted with type of reactions using pyridinium salts but it could variety of substituted benzylidene acetophenones not be duplicated until recently. With a view to (2) in refluxing glacial acetic acid to afford 2,4,6- explore the studies on the reactivity of pyridinium triarylsubstituted pyridines (4a-r), presumably via ylides toward a./5-unsaturated ketones we have 1,5-dionylpyridinium derivatives (3 a-r)3 (Scheme 1).

1a R'=H 1b R' = 4-0CH3 1c R' = 4-CH3 1d R '= 4-Br

Schem e 1

Similarly when the ylides (le,d) were allowed to react with 2-pyridylidene acetophenone ( 2, C6H 4- R ,,= 2-C 5HiN; R'"=4-Br), pyridines (5a,b) were isolated in 60-62% yields.

Requests for reprints should be sent to Dr. R. S. 5a R‘= 4 -CH3 j R”=4-Br T e w a r i , Department of Chemistry, Harcourt Butler Technological Institute, Kanpur-2, India. 5b R'= 4 -Br ; R"=4-Br P. S. KENDURKAR-R. S. TEWARI • N-PYRIDINIUM PHENANCYLIDES 553

When the ylides (la,d) were made to react with ylide (Id) with a-bromobenzylidene acetophenone dibenzylidene acetone (G) 2-stilbazoles (7a,b) were (8) in presence of ammonium acetate (Scheme 3). obtained analogously (Scheme 2). C6H5

Id + 1a,d

7b R = 4 -B r Scheme 3 Schem e 2 All the pyridines synthesized in this study are The synthesis of 2,3,4,6-tetrasubstituted pyridine listed in Table I. The general applicability of the derivative (9) was achieved by the interaction of synthesis is obvious from the inspection of Table I.

Table I. 2,4,6-Triarylsubstituted pyridines ((4a-r)-9).

Elemental IR data (KBr), Cm- P ro ­ Y ield R ecry stn. m.p. analysis CH stre- C = C and d u ct R'R" R'" [%] solvent [°C] Calcd./Found [%] telling C = N C H N vibrations vibrations

4a H H H 65 C5H 5N -E tO H 133-135a 89.90 5.53 4.56 3012 1603 1560 1502 (1:4) 89.89 5.52 4.56 4b H 3 ,4 -0 2CH 2 H 58 EtOH (90%) 152-153 82.05 4.67 3.97 82.00 4.64 3.96 4c H H 4-Br 65 CHCl3-MeOH 150-152b 71.50 4.04 3.53 (1:4) 71.48 4.01 3.50 4 d H 4-C1 4-Br 68 C5H 5N -M eO H 140 65.63 3.56 3.32 (1:4) 65.60 3.53 3.30 4 e H 2,4-diCl 4-Br 55 C5H 5N -M eO H 238-240 60.65 3.07 3.07 3021 1608 1541 1495 (1:4) 60.55 3.02 3.05 4f H 3 ,4 -0 2CH 2 4-Br 60 Et0H-H20 136-138 66.98 3.72 3.25 3003 1600 1546 1491 (1 : 1) 66.953.693.24 4g H 4 -N 0 2 4-Br 90 C5H 5N -M eO H 210-211 64.03 3.48 6.49 3012 1603 1548 1502 (1:4) 64.003.46 6.48 4h H 3 ,4 -0 2CH 2 4-O CH 3 62 CH Cl3-M eO H 103-105 78.74 4.98 3.67 3021 1610 1541 1502 (1:4) 78.72 4.96 3.66 4i H 4-OCH3 4-OCH3 60 C5H 5N -M eO H 101-104 81.74 5.72 3.81 3007 1608 1546 1511 (1:4) 18.73 5.73 3.80 4 j 4-OCH, 3,4-OoCH, 4-Br 58 CHCl3-MeOH 196-198 65.21 3.90 3.04 3021 1603 1548 1506 (1:4) 65.20 3.92 3.06 4k 4-OCH3 3,4-diOCH, H 60 C5H 5N -M eO H 170-172 78.58 5.79 3.52 3003 1616 1546 1511 (1:4) 78.38 5.74 3.50 41 4-CH3 4-C1 4-Br 60 E tO H (90% ) 132-133 66.28 3.91 3.22 3003 1600 1541 1506 66.24 3.90 3.20 4m 4-CH3 2,4-diCl H 55 C5H 5N -E tO H 78-80 73.84 4.35 3.58 (1:3) 73.82 4.30 3.54 4n 4-Br 4-OCH3 4-OCH3 65 CH Cl3-M eO H 149-151 67.26 4.48 3.13 3007 1603 1553 1493 (1:4) 67.25 4.43 3.12 4o 4-Br 4 -N 0 2 4-OCH3 85 C5H 5N -M eO H 235-236° 62.47 3.90 6.07 (1:4) 62.46 3.89 6.05 4p 4-Br 3 ,4 -0 2CH 2 4-OCH3 58 Me0H-H20 178-181 65.21 3.91 3.04 (1 : 1) 65.203.893.00 554 P. S. KENDURKAR-R. S. TEWARI • N-PYRIDINIUM PHENANCYLIDES

Elemental IR data (KBr),Cm -1 Pro- Yield Recrystn. m.p. Analysis CH stre- C = C and duct R' R" R"' [°/0] solvent [°C] Calcd./Found [°/0] telling C=N C H N vibrations vibrations

4q 4-Br 3,4-diOCHa 4-OCH3 55 C5H 5N -M eO H 112-115 65.54 4.62 2.98 (1:4) 65.50 4.61 3.00 4r 4-Br 3 ,4 -0 2CH 2 4-Br 63 CHCI3- M eOH 193-195 56.58 2.94 2.75 3021 1608 1551 1517 (1:4) 56.53 2.93 2.74 5a _-- 60 C5H 5N -M eO H 138-140 68.82 4.27 6.98 (1:4) 68.83 4.29 6.98 5b — -- 62 C5H 5N-MeOH 160-163 56.65 3.00 6.00 3040 1603 1548 1506 (1:4) 56.64 3.00 6.02 7 a — -- 60 CHCI3--MeOH 105-106d 90.09 5.70 4.20 (1:4) 90.05 5.69 4.20 7b __- 65 CHC13--MeOH 152-154 72.81 4.31 3.39 (1:4) 72.804.32 3.40 9 —-- 30 CHCI3--MeOH 92-95 50.75 2.57 2.57 3003 1616 1543 1493 (1:4) 50.73 2.55 2.55

a L it.6 138 °C; b Lit .7 154 °C; c L it.6 228-229 °C; d Lit .7 107 °C.

All the products, most of which are new, gave Pyridinium ylides (la-d) were prepared by treat­ correct elemental analysis. Their structures were ing cold aqueous solution of pyridinium salt with aqueous potassium carbonate or by treating pyri­ supported by IR (Table I) and NMR spectroscopy dinium salts with sodium hydride in dimethyl- (Table II). formamide solvent, according to the procedure of H e n r i c k et al.'°. All the reactions were carried out Table II. NMR spectra (CDC1;,) of 2,4,6-triarylsubsti- with freshly prepared pyridinium ylides. tuted pyridines. Preparation of 2,4,6-triarylsubstituted pyridines P ro d u ct ö [ppm] Number of Group (4a-r-5b), (Table I ) protons A general procedure was used in all the reactions. A mixture of N-pyridinium phenancylides (1 a-d) 4b 7.30--8.42, m 13H Phenyl 7.08, s 2H P y rid v l (0.003 mole) and ammonium acetate (3 g) in glacial 6.08, s 2H - o c h 2o - acetic acid was stirred at 80 °C. Benzylidene ketone 4i 7.50- 8.41, 111 13H Phenyl (2) (0.003 mole) in glacial acetic acid (10 ml) was 7.13, s 2H Pyridvl added dropwise during 1 h, after which time the 3.90, s 6H T w o ÖCH3 temperature was allowed to rise to 120 °C and 7 b 7.35--8.40, m 14H P henyl heating was continued for additional 3 h. The 7.14, s 2H P y rid y l mixture was left overnight at room temperature and 6.86, q 2H -C H = C H - ice-cold water (20 ml) w'as added to precipitate a

9 7.45- GC m 13H P henyl solid which was separated, washed with methanol 7.10, S 1 H P y rid y l and crystallized from appropriate solvent to yield 2,4,6-trisubstituted pyridine. ni = multiplet; s = singlet; q = quartet. Preparation of 2-benzylidene-4, 6-diphenyl pyri­ dines (7a-b) (Table I). Experimental Same procedure was used, except dibenzylidene- acetone ( 6) was used instead of benzylidene ketone. Melting points were measured on a Gallenkamp apparatus and are uncorrected. The IR spectra were recorded on Perkin-Elmer infracord spectro­ Preparation of 2.6-di-(4-bromop}ienyl)-4-phemyl-3- photometer in potassium bromide. The nuclear bromo pyridine (9) (Table I) magnetic resonance spectra (CDC13) were run using Above procedure was used, except a-bromobenzyl- a Varian A-60 spectrometer using tetramethylsilane idene acetophenone ( 8) was used in place of benzyl­ as an internal standard. Analytical samples were idene ketone. purified by column chromatography over neutral alumina. Purity was checked by thin layer chroma­ The authors wish to thank Dr. S . D. S h u k l a , tography (tic). Director and Professor R. C. S r i v a s t a v a , H. B. Pyridinium salts were prepared by the treatm ent Technological Institute, Kanpur-2, for providing of a-bromoketone or by heating a methyl ketone with facilities. PSK is thankful to the CSIR. New Delhi, iodine and pyridine using the procedure of K i n g 4. for the award of a Senior Research Fellowship. P. S. KENDURKAR-R. S. TEWARI • N-PYRIDINIUM PHENANCYLIDES 555

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