An efficient chemoselective synthesis of O-vinylaryl systems using acetylenic esters and dihydroxybenzenes in the presence of triphenylphosphine or alkyl isocyanides

Article abstract of DOI:10.1016/j.cclet.2009.10.007

The addition of 2,4-dihydroxyaceto(and benzo)phenone to propiolic ester is catalyzed by triphenylphosphine or tert-butyl isocyanide to form O-vinyl aryl derivatives in fairly good yields.

Full text of DOI:10.1016/j.cclet.2009.10.007

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Chinese Chemical Letters 21 (2010) 175–178
www.elsevier.com/locate/cclet
An efficient chemoselective synthesis of O-vinylaryl
systems using acetylenic esters and dihydroxybenzenes
in the presence of triphenylphosphine or alkyl isocyanides
*
Robabeh Baharfar , Mohammad Javad Taghizadeh,
Majid Ahmadian, Seyed Meysam Baghbanian
Department of Chemistry, University of Mazandaran, Babolsar 47415, Iran
Received 6 July 2009
Abstract
The addition of 2,4-dihydroxyaceto(and benzo)phenone to propiolic ester is catalyzed by triphenylphosphine or tert-butyl
isocyanide to form O-vinyl aryl derivatives in fairly good yields.
# 2009 Robabeh Baharfar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: 2,4-Dihydroxyaceto(and benzo)phenone; Triphenylphosphine; Propiolic ester; tert-Butyl isocyanide
Vinyl ethers of alcohols and phenols are well established monomers, building blocks and auxiliaries in organic
synthesis, steadily expanding their scope of applications [1–4]. The O-alkylated phenols have numerous industrial
applications, particularly in the production of dyes and agrochemicals [5–7].
We have already described the synthesis of O-vinyl, S-vinyl and N-vinyl systems from the reaction of
triphenylphosphine with propiolic esters and enols or thiols (as an OH- or SH-acid) [8–10]. With the purpose of the
study of chemoselectivity in bifunctional reagents, we selected 2,4-dihydroxy benzo(and aceto) phenones (2), which
have two OH acidic groups.
Therefore, the chemoselective reactions between OH-acids (1a,b) and propiolic esters in the presence of
triphenylphosphine or tert-butyl isocyanide lead to the synthesis of O-vinyl systems (3a–d) and C-vinyl systems (4a–
b) as by-products (Scheme 1).
1. Experimental
Melting points were measured on an Electrothermal 9100 apparatus. IR Spectra were measured on a Shimadzu IR-
460 spectrometer. 1H and 13C NMR spectra were measured with a Bruker DRX-500 AVANCE instrument with CDCl3
as solvent at 500.1 and 125.7 MHz, respectively. Mass spectra were recorded on a Finnigan-Matt 8430 mass
spectrometer operating at an ionization potential of 70 eV. 2,4-dihydroxy (aceto and benzo)phenone, propiolic esters,
* Corresponding author.
E-mail address: Baharfar@umz.ac.ir (R. Baharfar).
1001-8417/$ – see front matter # 2009 Robabeh Baharfar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2009.10.007

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R. Baharfar et al. / Chinese Chemical Letters 21 (2010) 175–178
Scheme 1. .
triphenylphosphine, tert-butyl isocyanide were obtained from Fluka (Buchs, Switzerland) and were used without
further purification.
1.1. General procedure
To a magnetically stirred solution of 2,4-dihydroxy aceto (or benzo)phenone (2 mmol) and propiolic ester (2 mmol)
in 10 mL of toluene was added dropwise at À10 8C over 10 min triphenylphosphine (1 mmol, 0.262 g) or tert-butyl
isocyanide (1 mmol). The reaction mixture was then allowed to warm up to room temperature and stand for 24 h. The
solvent was removed under reduced pressure and the residue was separated by silica gel column chromatography
(Merck 230–400 mesh) using n-hexane: ethylacetate as eluent.
Methyl-(E)-3-(4-acetyl-3-hydroxyphenoxy)-2- acrylate (3a): Yellow powder, mp 91–95 8C, yield 70%; IR
(KBr)(ymax, cmÀ1): 1640 (C O), 1735 (C O), 3400–3500 (OH); 1H NMR (500 MHz, CDCl3): d 2.61 (s, 3 H, CH3),
3.76 (s, 3 H, OCH3), 5.73 (d, 1 H, 3JHH =12.1 Hz, CH), 6.61(dd, 1 H, 3JHH = 8.8, 4JHH = 2.4 Hz, CH), 6.64 (d, 1 H,
3JHH = 2.4 Hz, CH), 7.75 (d,1 H, 3JHH = 8.8 Hz, CH), 7.81 (d, 1 H, 3JHH = 12.1 Hz, OCH), 12.57 (s, 1 H, OH); 13
C
NMR (125 MHz, CDCl3): d 26.6 (CH3), 51.5 (OCH3), 104.3 (C CH), 105.7, 108.5 and 132.8 (CH), 116.8, 161.4,
164.4 (3C), 156.1 (OCH CH), 167.0 (C O, ester), 203.0 (C O, ketone); MS, (m/z, %): 236 (M+, 57), 221 (M+–Me,
100), 177 [M+–(COCH3, Me, H), 34], 43 (COCH3 , 48).
+
Ethyl-(E)-3-(4-acetyl-3-hydroxyphenoxy)-2- acrylate (3b): Yellow powder, mp 95–99 8C, yield 65%; IR
1
(KBr)(ymax, cmÀ1): 1625(C O), 1765 (C O), 3360–3480 (OH); H NMR (500 MHz, CDCl3): d 1.28 (t, 3 H,
3JHH = 7.1 Hz, CH3), 2.56 (s, 3 H, CH3), 4.20–4.28 (m, 2 H, OCH2), 5.89 (d, 1 H, 3JHH = 12.1 Hz, CH), 6.35(dd, 1 H,
4
3
3
3JHH = 8.8, JHH = 2.4 Hz, CH), 6.41 (d, 1 H, JHH = 2.4 Hz, CH), 7.64 (d, 1 H, JHH = 8.8 Hz, CH), 7.71 (d, 1 H,
3JHH = 12.1 Hz, OCH), 12.69 (s, 1 H, OH);13C NMR (125 MHz, CDCl3): d 14.0 (CH3), 26.2 (CH3), 61.6 (OCH2),
103.5 (C CH), 103.6, 107.7 and 133.1 (CH), 114.3, 162.7, 165.1 (3C), 156.2 (OCH CH), 165.9 (C O, ester), 202.7
(C O, ketone); MS, (m/z, %): 250 (M+, 60), 221 (M+–Et, 100), 177 [M+–(COCH3, Et, H), 34], 43 (COCH3 , 50).
+
Methyl-(E)-3-(4-benzoyl-3-hydroxyphenoxy)-2-acrylate (3c): Yellow powder, mp 91–93 8C, yield 80%; IR
(KBr)(ymax, cmÀ1): 1625 (C O), 1765 (C O), 3300–3500 (OH); 1H NMR (500 MHz, CDCl3): d 3.76 (s, 3 H, OCH3),
5.75 (d, 1 H, 3JHH = 12.1 Hz, CH), 6.58 (dd, 1 H, 3JHH = 8.8, 4JHH = 2.4 Hz, CH), 6.74 (d, 1 H, 3JHH = 2.4 Hz, CH),
7.50–7.64 (m, 5 H, CH), 7.65 (d, 1 H, 3JHH = 8.8 Hz, CH), 7.84 (d, 1 H, 3JHH = 12.1 Hz, OCH), 12.44 (s, 1 H, OH); 13
C
NMR (125 MHz, CDCl3): d 51.5 (OCH3), 104.5 (C CH), 105.8, 108.2, 128.5, 129.0, 132.0, 135.8 (CH), 156.0
(OCH CH), 116.1, 137.8, 161.4, 165.6 (4C), 167.0 (C O, ester), 200.4 (C O, ketone); MS, (m/z, %): 298 (M+, 100),
105 (Ph–C O+, 92), 239 (M+–CO2Me, 35), 77 (ph+, 45).
Ethyl-(E)-3-(4-benzoyl-3-hydroxyphenoxy)-2-acrylate (3d): Yellow powder, mp 95–97 8C, yield 85%; IR
1
(KBr)(ymax, cmÀ1): 1625 (C O), 1770 (C O), 3350–3500 (OH); H NMR (500 MHz, CDCl3): d 1.31 (t, 3 H,
3
3
3JHH = 7.1 Hz, CH3), 4.22 (q, 2 H, JHH = 7.1 Hz, OCH2), 5.74 (d, 1 H, JHH = 12.1 Hz, CH), 6.58 (dd, 1 H,
3JHH = 8.8, JHH = 2.4 Hz, CH), 6.74 (d, 1 H, JHH = 2.4 Hz, CH), 7.49–7.64 (m, 5 H, CH), 7.65 (d, 1 H,
3JHH = 8.8 Hz, CH), 7.82 (d, 1 H, 3JHH = 12.1 Hz, OCH), 12.44 (s, 1 H, OH); 13C NMR (125 MHz, CDCl3): d 14.3
(CH3), 60.4 (OCH2), 104.9 (C CH), 105.8, 108.2, 128.4, 129.0, 132.0, 135.8 (CH), 155.9 (OCH CH), 116.1, 137.8,
161.5, 165.6 (4C), 166.6 (C O, ester), 200.4 (C O, ketone); MS, (m/z, %): 312 (M+, 100), 105 (Ph–C O+, 96), 239
(M+–CO2Et, 40), 77 (ph+, 39).
4
3

R. Baharfar et al. / Chinese Chemical Letters 21 (2010) 175–178
177
Methyl-2-(3-acetyl-2,6-dihydroxyphenyl)acrylate (4a): Yellow powder, mp 120–122 8C, yield 15%; IR
1
(KBr)(ymax, cmÀ1): 1625 (C O), 1765 (C O), 3400–3480 (OH); H NMR (500 MHz, CDCl3): d 2.68 (s, 3 H,
3
CH3), 3.80 (s, 3 H, OCH3), 6.11 (s, 1 H, OH), 6.47(s, 1 H, CH), 6.88 (d, 1 H, JHH = 9.0 Hz, CH), 7.96 (d, 1 H,
3JHH = 9.0 Hz, CH), 8.18 (s, 1 H, CH), 13.51 (s, 1 H, OH); 13C NMR (125 MHz, CDCl3): d 26.7 (CH3), 52.4 (OCH3),
107.7 and 133.8 (CH), 109.2, 115.3, 158.6 and 160.7 (4 C), 129.6 (C CH2), 135.8 ( CH2), 165.8 (C O, ester), 203.6
(C O, ketone); MS, (m/z, %): 236 (M+, 60), 221 (M+–Me, 100), 177 [M+–(COCH3, Me, H), 37], 43 (COCH3 , 40).
+
Ethyl-2-(3-acetyl-2,6-dihydroxyphenyl)acrylate (4b): Yellow powder, mp 140–145 8C, yield 20%; IR (KBr)(ymax,
cmÀ1): 1625 (C O), 1765 (C O), 3400–3450 (OH); 1H NMR (500 MHz, CDCl3): d 1.32 (t, 3 H, 3JHH = 7.1 Hz, CH3),
3
2.67 (s, 3 H, CH3), 4.29 (q, 2 H, JHH = 7.1 Hz, OCH2), 6.10 (s, 1 H, OH), 6.50 (s, 1 H, CH), 6.86 (d,1 H,
3JHH = 8.9 Hz, CH), 7.87 (d, 1 H, 3JHH = 8.9 Hz, CH), 8.18 (s, 1 H, CH), 13.50 (s, 1 H, OH); 13C NMR (125 MHz,
CDCl3): d 14.1 (CH3), 26.7 (CH3), 61.5 (OCH2), 107.7 and 133.5 (CH), 109.5, 115.3, 158.8 and 161.2 (4C), 129.4
(C CH2), 135.7 ( CH2), 165.4 (C O, ester), 203.6 (C O, ketone); MS, (m/z, %): 250 (M+, 60), 221 (M+–Et, 100),
177 [M+–(COCH3, Et, H), 35], 43 (COCH3 , 43).
+
2. Results and discussion
On the basis of the chemistry of trivalent phosphorus nucleophiles, it is reasonable to assume that O-vinyl and C-
vinyl 2,4-dihydroxyaceto(and benzo)phenone derivatives 3 and 4 result from the initial attack of triphenylphosphine
at the b–carbon atom of the propiolic ester to form dipolar intermediate (5). Then, concomitant protonation of
Scheme 2. .

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R. Baharfar et al. / Chinese Chemical Letters 21 (2010) 175–178
this 1:1 adduct by the OH-acid (1) leads to the corresponding phosphonium salt (6). The addition of the anion of (1)
(from O-head or C-head) to the (- or (-position of triphenylphosphonium acrylate counterpart (6) followed by
elimination of the triphenylphosphine to be recycled as a catalyst would lead to the O-vinyl and C-vinyl systems 3 and
4, respectively, Scheme 2. Tert-butyl isocyanide also catalyze this reaction via similar mechanism to produce the
same products.
The chemoselectivity of this reaction is explained by the deactivation of the hydroxy group by an intramolecular
hydrogen bonding with the neighboring carbonyl group. The structures of final products (3a–d) and by-products (4a–
1
b) were assigned to the isolated adducts on the basis of their elemental analysis, IR, H NMR, 13C NMR and mass
spectral data. Observation of two characteristic doublets with 3JHH of about 12 Hz in the 1H NMR spectra of (3a–d) is
consistent with O-vinylation of the aromatic ring and formation of alkyl (E)-aryloxy propenoates (3a–d). 1H NMR
spectra of (4a–b) revealed in each case, two single peaks at about ( = 6.50 and 8.18 ppm in agreement with the
diastereotopic protons in olefin moiety. The 13C NMR spectra of (3a–d) and (4a–b) show distinct resonances in
agreement with the proposed structures. Partial assignments of these resonances are given in the experimental section.
3. Conclusions
We have found a tri-component synthetic method for the preparation of some O-vinyl aryl derivatives of potential
synthetic interest. The present method carries the advantage that not only is the reaction performed under neutral
conditions, but also the starting materials and reagents can be mixed without any activation or modification.
References
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