INTRODUCTION:

Chroman-4-one derivatives are important class of compounds for the variety of biological activities. Major chroman-4-one derivatives are 3-benzylidene 4-chromones, flavanones, flavones, isoflavones and spirochromones. Flavonoids are generally polyphenolic compounds and widely distributed in nature. 3-benzylidene-2-phenylchroman-4-one also known as 3-arylidine flavanone or flavindogenides. Four rings (A,B,C and D) present in 3-benzylidene-2-phenylchroman-4-one.

Figure 1. Structure of 3-benzylidene-2-phenylchroman-4-one

3-benzylidene-2-phenylchroman-4-one derivatives can be synthesized from O-hydroxy acetohenone and substituted benzaldehyde using strong base as catalyst and alcohol as solvent.^1-4 Poor aqueous solubility of these compounds was reported. By using o-hydroxy acetophenone and benzaldehyde, 2’hydroxy chalcone synthesized and isomerizes using variety of catalyst to flavanone.^5-29 Title compounds can synthesize from flavanone and substituted benzaldehydes using acid or base catalyst. Piperidine was used as base catalyst for synthesis of target compounds, but yield was lower.³⁰HCl gas was reported as catalyst for synthesis of target compounds, but major drawback of this method is long reaction time and lower yield.³¹ Still there is no method available which is capable to gives higher yield and purity in very less time.

Chemistry:

Synthesis of 3-benzylidene-2-phenylchroman-4-one derivatives from flavanone and substituted benzaldehydes was carried out by using acid and base catalyzed methods. Anhydrous HCl, HCl 34% and p-TSA used as acid catalyst and piperidine, NaOH and Ba(OH)₂was used as base catalyst. Using different catalyst and conditions, trials was taken for comparison and selection of method for optimization. Method which gives higher yield was continue for examine of parameters effect on yield.

RESULTS AND DISCUSSION:

Table 1. Methods were tried for the synthesis of 3-benzylidene-2-phenylchroman-4-one analogs.

Sr No.	Catalyst	Solvent	Reaction condition	% yield
1	Piperidine	Methanol (if needed)	Reflux 24h	25
2	HCl Gas	Ethanol	28˚C, 48hr	No reaction
3	p-TSA	Methanol	Reflux, 72hr	No reaction
4	10% NaOH	Methanol	Stirred 24hr, 28˚C	5%
5	34% HCl	n-Butanol	Reflux 1h	7%
6	Anhydrous Ba(OH)₂	Methanol	Gradual Trituration	50%
7	NaOH	Methanol	Gradual Trituration	*

* By product formation; Amt. of reactants: 0.001mol

Table 2. Effect of catalyst quantity and solvent on product (3-benzylidene-2-phenylchroman-4-one analogs) yield.

Sr No.	Amount of Catalyst (gm)	Solvent	%yield
1	0.5	Methanol	10
2	1	Methanol	25.45
3	1.5	Methanol	56.12
4	2	Methanol	56.10
5	1.5	Ethanol	97%
6	1.5	IPA	15%
7	1.5	THF	No reaction
8	1.5	DCM	No reaction
9	1.5	ACN	2.47%

Amt. of reactants: 0.001mol, Amt of solvent: 2-5ml

Acid catalyst methods proved not effective for synthesis of compounds. Based catalyst methods like piperidine and 10% NaOH methods proved very less effective. Gradual trituration with barium hydroxide proved beneficial for synthesis of targeted compounds. Amount of barium hydroxide shows drastically change in %yield. % yield extremely increased when ethanol was used as a solvent.

Scheme 1. Synthesis of 3-benzylidene-2-phenylchroman-4-one analogs

Sr No	Comp. Code	R₁	R₂	R₃	R₄	Sr No	Comp. Code	R₁	R₂	R₃	R₄
1	B0	H	H	H	H	11	B10	H	H	N(CH₃)	H
2	B1	H	H	OCH₃	H	12	B11	H	H	Cl	H
3	B2	H	OCH₃	OCH₃	H	13	B12	Cl	Cl	H	H
4	B3	H	OCH₃	OCH₃	OCH₃	14	B13	Cl	H	H	NO₂
5	B4	H	OCH₃	OH	H	15	B14	NO₂	H	H	H
6	B5	H	H	OC₂H₅	H	16	B15	H	NO₂	H	H
7	B6	H	H	OC₃H₇	H	17	B16	H	H	NO₂	H
8	B7	H	H	CH₃	H	18	B17	OH	H	H	H
9	B8	H	H	C₂H₅	H	19	B18	H	H	OH	H
10	B9	H	H	C(CH₃)	H	-	-	-	-	-	-

CONCLUSION:

For the synthesis of 3-benzylidene-2-phenylchroman-4-one variety of acid and based catalyst methods are reported. Acid catalyst methods proved ineffective for synthesis of targeted compounds. Based catalyst methods shows very less efficacy for synthesis. Novel barium hydroxide trituration method proves highly effective. In this method very less amount of solvent required for synthesis. For the completion of reaction hardly 15-30 min required so this method proves time saving method. So our main aim of this study, to develop novel and eco-friendly method for synthesis of 3-benzylidene-2-phenylchroman-4-one derivatives was successfully completed.

EXPERIMENTAL:

Chemistry:

General:

All purchased chemicals were of analytical grade and used without further purification. Synthesis of 3-benzylidene-2-phenylchroman-4-one analogs (B0-B18) were carried out as per the procedure detailed in Scheme 1. The progress of the reactions was monitored by thin‐layer chromatography analysis (Silica gel G60 F254; Merck). Melting points of the synthesized compounds were determined in open capillary tubes using Veego Melting Point Apparatus model VMP-D. Infrared spectra were recorded on Perkin Elmer spectrum GX FTIR spectrophotometer using KBr discs. 1H-NMR was recorded on Bruker Advance–II NMR-400MHz instrument using DMSO as a solvent and tetra methyl silane (TMS) as internal standard. Mass spectra were recorded on LCQ Fleet and TSQ quantum surveyor plus HPLC system spectrophotometer.

General procedure for the synthesis of (E)-3-benzylidene-2-phenylchroman-4-one analogs:

Take equimolar amount of flavanone (0.001mol) and substituted benzaldehydes (0.001mol) in glass mortal pastel. Add 1.5 gm of anhydrous barium hydroxide and 2-5 ml of ethanol. Triturate reaction mixture so color change observed. After completion of reaction add 10% cold hydrochloric acid until mixture became acidify. Pour mixture in separating funnel and add 10ml n-Hexane. Shake well and collect n-hexane layer in porcelain dish. Evaporate n-hexane and collect bright yellow precipitate. Recrystallization was performed by using methanol: water (50:50).

(E)-3-benzylidene-2-phenylchroman-4-one (B0):

Pale yellow solid; %yield 97%; mp 102-104˚C; IR (KBr, cm^-1) vmax: 3065.45 (Aromatic C-H), 2922.21 (Aliphatic C-H), 1640.41 (C=O), 1450.66 (C=C), 1138.51 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 6.32 (s, 1H C₂-H), 7.52 (s, 1H, =CH), 6.88-7.80 (m, 14H aromatic CH); MS (ESI+): m/z 313 [M⁺]

(E)-3-(4-methoxybenzylidene)-2-phenylchroman-4-one (B1)

Pale yellow solid; %yield 95.2%; mp 98-101˚C; IR (KBr, cm^-1) vmax: 3076.13 (Aromatic C-H), 2912.25 (Aliphatic C-H), 1640.41 (C=O), 1470.15 (C=C), 1157.25 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 3.13 (s, 3H –OCH₃) 6.72 (s, 1H C₂-H), 7.85 (s, 1H, =CH), 7.05-7.85 (m, 13H aromatic CH); MS (ESI+): m/z 343 [M⁺]

(E)-3-(3,4-dimethoxybenzylidene)-2-phenylchroman-4-one (B2):

Pale yellow solid; %yield 92%; mp 96-98˚C; IR (KBr, cm^-1) vmax: 3080.13 (Aromatic C-H), 2956.51 (Aliphatic C-H), 1640.13 (C=O), 1518.15 (C=C), 1199.25 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 3.83 (s, 3H –OCH₃), 3.75 (s, 3H –OCH₃), 6.67 (s, 1H C₂-H), 7.40 (s, 1H, =CH), 7.05-7.85 (m, 12H aromatic CH); MS (ESI+): m/z 373 [M⁺]

(E)-3-(3,4,5-trimethoxybenzylidene)-2-phenylchroman-4-one (B3)

Pale yellow solid; %yield 92.5%; mp 95-99˚C; IR (KBr, cm^-1) vmax: 3076.54 (Aromatic C-H), 2937.17 (Aliphatic C-H), 1639.32 (C=O), 1510.54 (C=C), 1210.12 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 3.80 (s, 6H –OCH₃), 3.79 (s, 3H –OCH₃), 5.90 (s, 1H C₂-H), 7.56 (s, 1H, =CH), 6.91.-7.83 (m, 11H aromatic CH); MS (ESI+): m/z 403 [M⁺]

(E)-3-(4-hydroxy-3-methoxybenzylidene)-2-phenylchroman-4-one (B4)

Pale yellow solid; %yield 93.3%; mp 102-106˚C; IR (KBr, cm^-1) vmax: 3467.12 (-OH), 3025.43 (Aromatic C-H), 2984.65 (Aliphatic C-H), 1639.22 (C=O), 1480.65 (C=C), 1255.12 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 3.85 (s, 3H –OCH₃), 5.70 (s, 1H C₂-H), 7.47 (s, 1H, =CH), 6.81.-7.50 (m, 12H aromatic CH), 12.24 (s, 1H -OH); MS (ESI+): m/z 359.45 [M⁺]

(E)-3-(4-ethoxybenzylidene)-2-phenylchroman-4-one B5

Pale yellow solid; %yield 83.4%; mp 104-108˚C; IR (KBr, cm^-1) vmax: 3036.45 (Aromatic C-H), 2981.64 (Aliphatic C-H), 1640.45 (C=O), 1482.15 (C=C), 1243.31 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 2.01 (t, 3H CH₃-CH₂), 3.97 (q, 2H CH₃-CH₂-O), 5.82 (s, 1H C₂-H), 7.45 (s, 1H, =CH), 7.12-8.15 (m, 13H aromatic CH); MS (ESI+): m/z 357 [M⁺]

(E)-3-(4-propoxybenzylidene)-2-phenylchroman-4-one B6

Pale yellow solid; %yield 85%; mp 110-112˚C; IR (KBr, cm^-1) vmax: 3037.42 (Aromatic C-H), 2974.45 (Aliphatic C-H), 1639.35 (C=O), 1484.54 (C=C), 1253.74 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 1.35 (t, 3H CH₃-CH₂), 1.98 (h, 2H CH₃-CH₂-CH₃), 3.83 (q, 2H CH₂-CH₂-O), 5.79 (s, 1H C₂-H), 7.53 (s, 1H, =CH), 7.2-8.01 (m, 13H aromatic CH); MS (ESI+): m/z 371 [M⁺]

(E)-3-(4-methylbenzylidene)-2-phenylchroman-4-one B7

Pale yellow solid; %yield 90%; mp 107-109˚C; IR (KBr, cm^-1 ) vmax: 3067.52 (Aromatic C-H), 2983.42 (Aliphatic C-H), 1639.54 (C=O), 1459.54 (C=C), 1254.74 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 2.12 (s, 3H CH₃), 5.65 (s, 1H C₂-H), 7.43 (s, 1H, =CH), 7.03-7.85 (m, 13H aromatic CH); MS (ESI+): m/z 327 [M⁺]

(E)-3-(4-ethylbenzylidene)-2-phenylchroman-4-one B8

Pale yellow solid; %yield 87%; mp 112-115˚C; IR (KBr, cm^-1) vmax: 3056.54 (Aromatic C-H), 2972.35 (Aliphatic C-H), 1640.53 (C=O), 1480.11 (C=C), 1276.15 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 1.57(t, 3H CH₃-CH₂), 2.52 (q, 2H CH₃-CH₂), 5.72 (s, 1H C₂-H), 7.35 (s, 1H, =CH), 6.93-8.05 (m, 13H aromatic CH); MS (ESI+): m/z 340 [M⁺]

(E)-3-(4-isopropylbenzylidene)-2-phenylchroman-4-one B9

Pale yellow solid; %yield 84.5%; mp 110-115˚C; IR (KBr, cm^-1) vmax: 3078.45 (Aromatic C-H), 2981.21 (Aliphatic C-H), 1640.03 (C=O), 1473.22 (C=C), 1246.51 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 1.57(d, 6H (CH₃)₂-CH), 4.81 (m, 1H (CH₃)₂-CH), 5.52 (s, 1H C₂-H), 7.53 (s, 1H, =CH), 7.03-8.05 (m, 13H aromatic CH); MS (ESI+): m/z 355 [M⁺]

(E)-3-(4-(dimethylamino)benzylidene)-2-phenylchroman-4-one B10

Pale yellow solid; %yield 91.2%; mp 98-104˚C; IR (KBr, cm^-1 ) vmax: 3081.54 (Aromatic C-H), 2942.52 (Aliphatic C-H), 1640.45 (C=O), 1490.25 (C=C), 1250.21 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 3.12(s, 6H (CH₃)₂-N), 5.72 (s, 1H C₂-H), 7.45 (s, 1H, =CH), 6.82-7.95 (m, 13H aromatic CH); MS (ESI+): m/z 356 [M⁺]

(E)-3-(4-chlorobenzylidene)-2-phenylchroman-4-one B11

Pale yellow solid;%yield 90.5%; mp 107-109˚C; IR (KBr, cm^-1) vmax: 3096.02 (Aromatic C-H), 2985.25 (Aliphatic C-H), 1640.42 (C=O), 1459.52 (C=C), 1274.54 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.53 (s, 1H C₂-H), 7.49 (s, 1H, =CH), 6.96-8.15 (m, 13H aromatic CH); MS (ESI+): m/z 346 [M⁺], 348[M⁺²]

(E)-3-(2,3-dichlorobenzylidene)-2-phenylchroman-4-one B12

Pale yellow solid; %yield 95%; mp 101-104˚C; IR (KBr, cm^-1) vmax: 3071.52 (Aromatic C-H), 2965.85 (Aliphatic C-H), 1639.25 (C=O), 1463.45 (C=C), 1265.64 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.61 (s, 1H C₂-H), 7.56 (s, 1H, =CH), 7.06-8.25 (m, 12H aromatic CH); MS (ESI+): m/z 381 [M⁺], 383[M⁺²]

(E)-3-(2-chloro-5-nitrobenzylidene)-2-phenylchroman-4-one B13

Pale yellow solid; %yield 95%; mp 101-104˚C; IR (KBr, cm^-1 ) vmax: 3067.12 (Aromatic C-H), 2950.12 (Aliphatic C-H), 1640.45 (C=O), 1554.12 (N-O), 1472.54 (C=C), 1264.45 (C-O), 1104.12 (C-N); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.72 (s, 1H C₂-H), 7.45 (s, 1H, =CH), 6.97-8.05 (m, 12H aromatic CH); MS (ESI+): m/z 391 [M⁺], 392[M⁺¹], 393[M⁺²]

(E)-3-(2-nitrobenzylidene)-2-phenylchroman-4-one B14

Pale yellow solid; %yield 89.5%; mp 102-105˚C; IR (KBr, cm^-1) vmax: 3084.57 (Aromatic C-H), 2915.21 (Aliphatic C-H), 1643.12 (C=O), 1564.44 (N-O), 1479.12 (C=C), 1276.12 (C-O), 1146.12 (C-N); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.75 (s, 1H C₂-H), 7.51 (s, 1H, =CH), 6.90-8.15 (m, 13H aromatic CH); MS (ESI+): m/z 357 [M⁺]

(E)-3-(3-nitrobenzylidene)-2-phenylchroman-4-one B15

Pale yellow solid; %yield 86.1%; mp 105-107˚C; IR (KBr, cm^-1) vmax: 3074.25 (Aromatic C-H), 2984.01 (Aliphatic C-H), 1647.12 (C=O), 1545.54 (N-O), 1445.45 (C=C), 1284.45 (C-O), 1145.45 (C-N); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.81 (s, 1H C₂-H), 7.38 (s, 1H, =CH), 7.12-8.25 (m, 13H aromatic CH); MS (ESI+): m/z 357[M⁺]

(E)-3-(4-nitrobenzylidene)-2-phenylchroman-4-one B16

Pale yellow solid; %yield 89.8%; mp 109-112˚C; IR (KBr, cm^-1) vmax: 3045.15 (Aromatic C-H), 2965.56 (Aliphatic C-H), 1639.15 (C=O), 1546.12 (N-O), 1435.45 (C=C), 1259.12 (C-O), 1151.12 (C-N); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 5.73 (s, 1H C₂-H), 7.51 (s, 1H, =CH), 7.09-8.17 (m, 13H aromatic CH); MS (ESI+): m/z 357[M⁺]

(E)-3-(2-hydroxybenzylidene)-2-phenylchroman-4-one B17

Pale yellow solid; %yield 86%; mp 95-99˚C; IR (KBr, cm^-1) vmax: 3446.21 (-OH), 3081.12 (Aromatic C-H), 2975.45 (Aliphatic C-H), 1639.55 (C=O), 1453.12 (C=C), 1254.12 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 12.01 (s, 1H -OH), 5.70 (s, 1H C₂-H), 7.80 (s, 1H, =CH), 6.79-8.10 (m, 13H aromatic CH); MS (ESI+): m/z 329[M⁺]

(E)-3-(4-hydroxybenzylidene)-2-phenylchroman-4-one B18

Pale yellow solid; %yield 85.5%; mp 98-100˚C; IR (KBr, cm^-1) vmax: 3481.12 (-OH), 3065.21 (Aromatic C-H), 2965.12 (Aliphatic C-H), 1639.46 (C=O), 1454.12 (C=C), 1272.12 (C-O); ¹H NMR (400 MHz, DMSOd₆) δ ppm: 12.35 (s, 1H -OH), 5.75 (s, 1H C₂-H), 7.65 (s, 1H, =CH), 6.90-7.95 (m, 13H aromatic CH); MS (ESI+): m/z 329[M⁺]

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Received on 29.01.2022 Modified on 05.04.2022

Asian J. Research Chem. 2022; 15(3):195-199.

DOI: 10.52711/0974-4150.2022.00033