Synthesis of functionalized fused-ring heterocycles from tautomers of 2-(thiazole, oxazole, benzothiazole, and benzoxazole)-1-phenylethenols and 1,3-diacid chlorides or N-(chlorocarbonyl) isocyanate

Article abstract of DOI:10.1055/s-0032-1316800

2-Methylthiazole, 2,4,5-trimethylthiazole, 2,4,5-trimethyloxazole, 2-methylbenzothiazole, and 2-methylbenzoxazole were each reacted with benzoyl chloride in acetonitrile-triethylamine to generate (Z)-2-(heterocyclic)-1- phenylvinyl benzoates. Base hydrolysis of these vinyl benzoates formed (Z)-2-(heterocyclic)-1-phenylethenols, which exist in both keto and enol tautomeric forms. These tautomers were used as starting materials for fused-ring heterocycle syntheses. Reactions with 2,2-dialkyl-1,3-diacid chlorides in acetonitrile-triethylamine afforded their corresponding 5,6-ring-fused 8-benzoyl-6,6-dialkyl-6H-thiazolo-, 8-benzoyl-2,3,6,6-tetramethyl-6H-thiazolo-, 8-benzoyl-2,3,6,6-tetramethyl-6H-oxazolo-, 4-benzoyl-2,2-dimethyl-1H-benzo[4,5] thiazolo-, and 4-benzoyl-2,2-dimethyl-1H-benzo[4,5]oxazolo[3,2,-a]pyridinedione derivatives. The 5,6,6-tri-ring fused species, 10-benzoyl-7,8-dihydropyrano[2,3- d]thiazolo[3,2-a]pyridin-5(6H)-one, was formed in the reaction of the tautomers of (Z)-1-phenyl-2-(thiazol-2-yl)ethenol with cyclobutane-1,1-dicarbonyl dichloride via a ring expansion after 5,6-ring fusion. Functionalized 5,6-ring-fused 8-benzoyl-6H-thiazolo- and 8-benzoyl-6H-oxazolo[3,2-f]pyrimidine- 5,7-diones, and 4-benzoyl-1H-benzo[4,5]thiazolo- and 4-benzoyl-1H-benzo[4,5] oxazolo[3,2-c]pyrimidine-1,3(2H)-diones were also synthesized by reacting the (Z)-2-(heterocyclic)-1-phenylethenol tautomers with N-chlorocarbonyl isocyanate in THF-triethylamine. Georg Thieme Verlag KG - Stuttgart - New York.

Full text of DOI:10.1055/s-0032-1316800

Journal of Synthetic 0rganic Chemistry
SUPPORTING INFORMATION
SYNTHESIS
Supporting Information
for DOI: 10.1055/s-0032-1316800
© Georg Thieme Verlag KG Stuttgart · New York 2012
Thieme

Synthesis of functionalized fused-ring heterocycles from tautomers of 2-
(thiazole, oxazole, benzothiazole and benzoxazole)-1-phenylethenols
and 1,3-diacid chlorides or N-(chlorocarbonyl) isocyanate
Hondamuni I. De Silva,*Sabornie Chatterjee, William P. Henry, Charles U. Pittman Jr.*
Department of Chemistry, Mississippi State University, Mississippi State,
MS 39762, USA
Supporting Information
Chemicals were purchased from commercial suppliers and used as received, except that
cyclobutane-1,1-dicarbonyl dichloride was synthesized by treating cyclobutane-1,1-dicarboxylic
acid with thionyl chloride. Acetonitrile and triethylamine were distilled from calcium hydride
under nitrogen. Tetrahydrofuran (THF) was distilled from Na metal/benzophenone ketyl. The
dried CH3CN and THF were freshly distilled prior to use. All reactions were carried out under
nitrogen. Silica gel (230-400 mesh and a pore size 60 Ǻ) purchased from Sorbent Technologies,
was used as the stationary phase for flash chromatography analyses. 1H NMR and 13C NMR
spectra were recorded on a Bruker AVANCE III -300 or -600 spectrometers operating at 300
MHz and 600 MHz for proton, and 75 MHz and 150 MHz for carbon. Chemical shifts were
reported in parts per million (ppm) on the delta (δ) scale relative to the internal standard,
tetramethylsilylane for 1H (δ = 0 ppm) and the center line of the deuterated solvent for 13C
(CDCl3: δ = 77.0 ppm and DMSO-d6: = 39.43 ppm). Splitting patterns are designed as “s, d, t,
q, and m”, and these symbols indicate “singlet, doublet, triplet, quartet, and multiplet,”
respectively. Coupling constants, J, were reported in Hertz (Hz). High-resolution mass spectra
were recorded on a Bruker UHPLC-micro-Q/T MS/MS spectrometer in the ESI mode. Melting

points were recorded with a Mel-Temp apparatus and were uncorrected. IR spectra were
recorded on a Nicolet 6700 FT-IR spectrometer. A Bruker AXS Smart 1000 diffractometer,
upgraded with an APEX II detector and software which incorporates SHELX components,1 was
employed for crystal structure determinations at -173 C. All reactions were carried out under
nitrogen.
Preparation of enol-esters of thiazoles, oxazoles, benzoxazoles and benzothiazoles
(Z)-1-Phenyl-2-(thiazol-2-yl)vinyl benzoate (31)2
Triethylamine (1.83 g, 18.1 mmol, 3.6 eq.) was added to a stirred solution of 2-methylthiazole 29
(0.496 g, 5 mmol, 1 eq.) in CH3CN (25 mL) at room temperature under nitrogen. Benzoyl
chloride (2.13 g, 15 mmol, 3 eq.) in acetonitrile (20 mL) was added dropwise into this solution at
room temperature under nitrogen. This solution was refluxed for 7 h. After cooling to room
temperature, acetonitrile was removed by rotary evaporation. The residue was dissolved in
dichloromethane (30 mL), washed with saturated aqueous NaHCO3 (2 × 30 mL) and dried over
anhydrous sodium sulfate and filtered. After removal of dichloromethane by rotary evaporation,
the crude product was purified by column chromatography (silica gel, ethyl acetate/hexane = 1:3)
to give the title compound 31 (1.364 g, 88.8%). This general procedure was also used for the
syntheses of compounds 32, 33, 34-35 discussed in this section.
Yellow solid; mp = 105-106 C; Rf = 0.39 (ethyl acetate/hexane = 1:3).
IR (neat): 3116, 3069, 3032, 2981, 1732, 1642, 1599, 1448, 1235, 1175, 1076, 1058, 1023, 762,
707, 692 cm-1.
1H NMR (300 MHz, CDCl3): 8.33 (d, J = 7.48 Hz, OCOC6H5 ortho, 2H), 7.82 (d, J = 3.0 Hz,
=NCH=CHS , 1H), 7.71 (t, J = 7.40 Hz, OCOC6H5 para, 1H), 7.63-7.55 and 7.37-7.40 (m,

OCOC6H5 meta, CH=C(C6H5)O ortho, meta and para, and N,SุCCH= , 8H), 7.25 (d, J =
3.0 Hz, =NCH=CHS , 1H).
13C NMR (150 MHz, CDCl3): 163.68 ( OCOC6H5), 161.42 (N,SุC ), 150.18
( CH=C(C6H5)O ), 142.77 (=NCH=CHS ), 134.13 ( OCOC6H5 para), 133.85
( OCOC6H5 ipso), 130.57 ( OCOC6H5 ortho), 129.63 ( CH=C(C6H5)O para), 128.89
( OCOC6H5 meta), 128.85 ( CH=C(C6H5)O meta), 128.82 ( CH=C(C6H5)O ipso), 124.96
( CH=C(C6H5)O ortho), 119.66 (=NCH=CHS ), 112.08 (N,SุCCH=).
DEPT 135 NMR (150 MHz, CDCl3): 142.86, 134.23, 130.62, 129.73, 128.99, 128.92, 125.06,
119.76, 112.18.
(Z)-2-(4,5-dimethylthiazol-2-yl)-1-phenylvinyl benzoate (32)2
The title compound 32 (1.11 g, 66.1%) was obtained using 2,4,5-trimethylthiazole 21 (0.636 g, 5
mmol, 1 eq.), triethylamine (1.84 g, 18 mmol, 3.6 eq.) and benzoyl chloride (2.13 g, 15 mmol, 3
eq.) by the general procedure used for the synthesis and purification of 31. Ethyl acetate/hexane
= 1:3 was used as the eluent for column chromatography.
Yellow solid; mp = 156-158 C.; Rf = 0.50 (ethyl acetate/hexane =1:3).
IR (neat): 3066, 3045, 2951, 2915, 1741, 1655, 1537, 1450, 1432, 1227, 1076, 1050, 1023, 885,
767, 694 cm-1.
1H NMR (300 MHz, CDCl3): 8.33 (d, J = 7.55 Hz, OCOC6H5 ortho, 2H), 7.72 (t, J = 7.40
Hz, OCOC6H5 para, 1H), 7.62-7.56 and 7.38-7.35 (m, OCOC6H5 meta, and CH=C(C6H5)O
ortho, meta and para, 7H), 7.23 (s, N,SุCCH=, 1H), 2.31 (s, =NC(CH3)=C(CH3)S or
=NC(CH3)=C(CH3)S , 3H), 2.28 (s, =NC(CH3)=C(CH3)S or =NC(CH3)=C(CH3)S , 3H).
13C NMR (150 MHz, CDCl3): 163.84 ( OCOC6H5 or N,SุC ), 156.69
( OCOC6H5 or N,SุC ), 148.75 ( CH=C(C6H5)O or =NC(CH3)=C(CH3)S ), 148.38
( CH=C(C6H5)O or =NC(CH3)=C(CH3)S ), 134.03 ( OCOC6H5 ipso), 134.01

( OCOC6H5 para), 130.54 ( OCOC6H5 ortho), 129.29 ( CH=C(C6H5)O para), 129.00
( OCOC6H5 ipso), 128.85 ( OCOC6H5 meta or CH=C(C6H5)O meta), 128.79
( OCOC6H5 meta or CH=C(C6H5)O meta), 127.80 (=NC(CH3)=C(CH3)S ), 124.73
( CH=C(C6H5)O ortho), 112.24 (N,SุCCH=), 14.54 (=NC(CH3)=C(CH3)S or
=NC(CH3)=C(CH3)S ), 11.35 (=NC(CH3)=C(CH3)S or =NC(CH3)=C(CH3)S ).
DEPT 135 NMR (150 MHz, CDCl3): 134.09, 130.81, 129.37, 128.93, 128.87, 124.81, 112.32,
14.62, 11.43.
(Z)-2-(4,5-dimethyloxazol-2-yl)-1-phenylvinyl benzoate (33)2
The title compound 33 (1.26 g, 78.9%) was obtained using 2,4,5-trimethyloxazole 22 (0.585 g, 5
mmol, 1 eq.), triethylamine (1.87 g, 18.5 mmol, 3.7 eq.) and benzoyl chloride (2.15 g, 15.1
mmol, 3 eq.). The general procedure used for both the synthesis and purification of 31 was
followed. The crude product was purified by column chromatography using ethyl acetate/hexane
= 1:4 over silica gel.
Sticky oil; Rf = 0.54 (ethyl acetate/hexane =0.3).
IR (neat): 3062, 2978, 2953, 2923, 2858, 1738, 1633, 1449, 1236, 1175, 1082, 1064, 1024, 1000,
760, 705, 689 cm-1.
1H NMR (300 MHz, CDCl3): 8.27 (d, J = 7.47 Hz, OCOC6H5 ortho, 2H), 7.69-7.37 (m,
OCOC6H5 meta and para, and CH=C(C6H5)O ortho, meta and para, 8H), 6.83 (s, N,SุCCH=,
1H), 2.01 (s, =NC(CH3)=C(CH3)O or =NC(CH3)=C(CH3)O , 3H), 1.92 (s,
=NC(CH3)=C(CH3)O or =NC(CH3)=C(CH3)O , 3H).
13C NMR (150 MHz, CDCl3): 164.62 ( OCOC6H5 or N,OุC ), 155.83
( OCOC6H5 or N,OุC ), 149.71 ( CH=C(C6H5)O or =NC(CH3)=C(CH3)O ), 143.42
( CH=C(C6H5)O or =NC(CH3)=C(CH3)O ), 133.82 ( OCOC6H5 ipso), 133.42
( OCOC6H5 para), 132.00 ( CH=C(C6H5)O ipso), 130.16 ( OCOC6H5 ortho), 129.54

( CH=C(C6H5)O para), 129.73 (=NC(CH3)=C(CH3)O ), 128.69 ( OCOC6H5 meta or
CH=C(C6H5)O meta), 128.37 ( OCOC6H5 meta or CH=C(C6H5)O meta), 124.86
( CH=C(C6H5)O ortho), 103.10 (N,OุCCH=), 10.92 (=NC(CH3)=C(CH3)O or
(=NC(CH3)=C(CH3)O ), 9.59 (=NC(CH3)=C(CH3)O or (=NC(CH3)=C(CH3)O ).
DEPT 135 NMR (150 MHz, CDCl3): 133.62, 130.35, 129.73, 128.88, 128.56, 125.05, 103.29,
11.11, 9.78.
(Z)-2-(benzo[d]thiazol-2-yl)-1-phenylvinyl benzoate (34)
The title compound 17 (1.89 g, 53%) was prepared from 2-methylbenzothiazole 27 (1.51 g, 10
mmol, 1 eq.), triethylamine (3.71 g, 36.7 mmol, 3.7 eq.) and benzoyl chloride (4.26 g, 30 mmol,
3 eq.) by the general procedure used for the synthesis and purification of 31. Ethyl
acetate/hexane = 1:6 was used as the eluent for column chromatography over silica gel.
Yellow solid; mp = 146-148 C; Rf = 0.54 (ethyl acetate/hexane = 1:4).
IR (neat): 3061, 2981, 1739, 1641, 1596, 1452, 1445, 1432, 1227, 1209, 1175, 1080, 1055, 1023,
1000, 850, 754, 656 cm-1.
1H NMR (600 MHz, CDCl3): 8.36 (d, J = 7.80 Hz, OCOC6H5 ortho, 2H), 7.97 (d, J = 8.19
Hz, aromatic H in benzothiazole ring, 1H), 7.73 (dd, J = 7.80 and 7.61 Hz, OCOC6H5 meta,
2H) 7.65 (d, J = 7.65 Hz, CH=C(C6H5)O ortho, 2H), 7.60 (dd, J = 7.65 and 7.56 Hz,
CH=C(C6H5)O meta, 2H), 7.45-7.39 (m, OCOC6H5 para, three aromatic CHs on the
benzothiazole ring and
CH=C(C6H5)O , 5H), 7.31 (t, J = 7.56 Hz, CH=C(C6H5)O para, 1H).
13C NMR (150 MHz, CDCl3): 163.71 ( OCOC6H5 or N,SุC ), 161.38
( OCOC6H5 or N,SุC ), 152.57 ( CH=C(C6H5)O or C next to S in the benzothiazole ring),
152.48 ( CH=C(C6H5)O or C next to S in the benzothiazole ring), 135.05 (C next to N in the
benzothiazole ring), 134.20 ( OCOC6H5 para), 133.73 ( OCOC6H5 ipso), 130.63 ( OCOC6H5

ortho), 130.05 ( CH=C(C6H5)O para), 128.95 ( OCOC6H5 meta or ( CH=C(C6H5)O meta),
128.88 ( OCOC6H5 meta or ( CH=C(C6H5)O meta), 128.80 ( CH=C(C6H5)O ipso), 126.25
and 125.32 (aromatic CHs on the benzothiazole ring), 125.21 ( CH=C(C6H5)O ortho), 123.00
and 121.29 (aromatic CHs on the benzothiazole ring), 112.44 (N,SุCCH=).
DEPT 135 NMR (150 MHz, CDCl3): 134.32, 130.74, 130.17, 129.07, 129.00, 126.37, 125.44,
124.33, 123.12, 121.41. 112.56.
(Z)-2-(benzo[d]oxazol-2-yl)-1-phenylvinyl benzoate (35)
The title compound 35 (2.94 g, 43%) was obtained by the reaction of 2-methyl-benzoxazole 30
(2.69 g, 20 mmol, 1 eq.), triethylamine (7.48 g, 74 mmol, 3.7 eq.) and benzoyl chloride (8.51 g,
60.5 mmol, 3 eq.). The general procedure used for the synthesis and purification of 31 was
employed. The eluent used for column chromatography over silica gel was ethyl acetate/hexane
= 1:5.
White crystalline solid; mp = 97-98 C; Rf = 0.58 (ethyl acetate/hexane = 1:4).
IR (neat): 3078, 1731, 1644, 1605, 1540, 1451, 1234, 1181, 1152, 1084, 1067, 1027, 946, 848,
790, 746, 701, 687 cm-1.
1H NMR (300 MHz, CDCl3): 8.32 (d, J = 7.68 Hz, OCOC6H5 ortho, 2H), 7.71-7.67, 7.60-
7.54, 7.41-7.40 and 7.24-7.18 (m, OCOC6H5 meta and para,
CH=C(C6H5)O ortho, meta and the four aromatic CHs on the benzoxazole ring, 11H), 7.11 (d,
J = 8.04 Hz, CH=C(C6H5)O para, 1H) 7.04 (s, CH=C(C6H5)O , 1H).
13C NMR (150 MHz, CDCl3): 164.47 ( OCOC6H5 or N,OุC ), 159.75
( OCOC6H5 or N,OุC ), 154.09 ( CH=C(C6H5)O or C next to O in the benzoxazole ring),
150.06 ( CH=C(C6H5)O or C next to O on the benzoxazole ring), 141.57 (C next to N on the
benzoxazole ring), 133.67 ( OCOC6H5 para), 133.58 ( OCOC6H5 ipso), 130.45
( CH=C(C6H5)O para), 130.41 ( OCOC6H5 ortho), 129.37 ( CH=C(C6H5)O ipso), 128.87

( OCOC6H5 meta or CH=C(C6H5)O meta), 128.56 ( OCOC6H5 meta or ( CH=C(C6H5)O
meta), 125.48 ( CH=C(C6H5)O ortho), 125.19, 124.39, 119.95 and 110.12 (aromatic CHs on
the benzoxazole ring), 103.22 (N,OุCCH=).
DEPT 135 NMR (150 MHz, CDCl3): 133.84, 130.61, 130.58, 129.04, 128.72, 125.64, 125.36,
124.56, 120.11, 110.29. 103.38.
Synthesis of the equilibrating tautomers of 2-(thiazole, oxazole, benzoxazole and
benzothiazole)-1-phenylethenols
(Z)-1-phenyl-2-(thiazol-2-yl)ethenol (1a) and 1-phenyl-2-(thiazol-2-yl)ethanone (1b)
(Z)-1-Phenyl-2-(thiazol-2-yl)vinyl benzoate 31 (2.144 g, 6.98 mmol, 1 eq.) was dissolved in
anhydrous MeOH (15 mL). KOH (0.788 g, 14.04 mmol, 2 eq.), dissolved in MeOH (10 mL),
was added dropwise into this solution and stirred for 24 h at room temperature. Then MeOH was
removed by rotary evaporation. The residue was dissolved in water (30 mL), neutralized with
1M H2SO4 and extracted with dichloromethane (25 mL × 2). The organic layer was further
washed with water (30 mL), dried over anhydrous sodium sulfate and filtered. After removal of
dichloromethane by rotary evaporation, the crude product was purified by column
chromatography (silica gel, ethyl acetate/hexane = 1:4) to isolate the titled compounds (1.273 g,
89.8%). 1H and 13C NMR in CDCl3 confirmed that the isolated product consists of the
equilibrating tautomers (Z)-1-phenyl-2-(thiazol-2-yl)ethenol 1a and 1-phenyl-2-(thiazol-2-
yl)ethanone 1b in a 1:2.0 ratio.
Tautomers 1a and 1b (0.971 g, 97%) were isolated in another batch by reacting (Z)-1-phenyl-2-
(thiazol-2-yl)vinyl benzoate 31 (1.509 g, 4.9 mmol) and KOH (0.554 g, 9.87 mmol, 2 eq.) in 30
mL of anhydrous MeOH. This general procedure was used for the hydrolysis of enol-esters 32,
33, 34 and 35 to isolate corresponding equilibrating tautomers of 3-6, respectively.
Dark green oil; Rf = 0.48 (ethyl acetate/hexane = 1:3).

IR (neat): 3117, 3084, 3060, 1687, 1622, 1598, 1576, 1494, 1483, 1449, 1263, 1210, 1100, 1070,
752, 686, 632 cm-1.
1H NMR (600 MHz, CDCl3):
(broad OH, 1H), 7.99 (d, J = 7.56 Hz, C6H5 ortho in 1b,
2H), 7.74 (d, J = 7.95 Hz, ortho in 1a, 2H), 7.70 (d, J = 3.25, =NCH=CHS in 1b, 1H), 7.61 (d,
J = 3.32 Hz, =NCH=CHS in 1a, 1H), 7.53 (t, J = 7.37 Hz, C6H5 meta in 1a, 2H), 7.42 (t, J =
7.70 Hz, C6H5 meta in 1b, 2H), 7.35-7.31 (m, para in both 1a and 1b, 2H), 7.26 (d, J = 3.25 Hz,
=NCH=CHS in 1b, 1H), 7.00 (d, J = 3.32 Hz, =NCH=CHS in 1a, 1H), 6.28 (s, =CH in 1a,
1H), 4.69 (s, CH2 in 1b, 2H).
The areas of the peaks for 1a and 1b were considered separately since their mole ratio in the
solution was not 1:1. All peaks were first integrated by setting the area of the vinyl proton (=CH)
peak of the enol tautomer 1a at 6.28 ppm at one versus the rest of the resonances for 1a. The area
of the methylene protons ( CH2) of the keto tautomer 1b at 4.69 ppm was set at two versus the
rest of the resonances for 1b. The integration values of each peak and coupling patterns were
used when assigning proton signals for the each tautomer. To obtain the mole ratio between 1a
and 1b in CDCl3, the integrated area of the CH2 at 4.69 ppm was set at two and then the =CH
peak at 6.28 ppm was integrated and found to have an area of 0.5 versus the integrated area of
the methylene proton peak of the keto form. The enol =CH peak corresponds to one proton per
molecule and the keto CH2 peak corresponds to two protons per molecule. Therefore, to calculate
the mole ratio between 1a and 1b, half of the keto CH2 integrated area (1.0) of 1b was divided by
the enol =CH integrated area (0.5). This gave 1:2.0 ratio for 1a:1b.
13C NMR (150 MHz, CDCl3): 194.46 ( CH2CO in 1b), 168.35 (=C(OH) in 1a), 162.15 and
160.64 (N,SุC in 1a and 1b), 142.10 and 140.11 (>NCH=CHS in 1a and 1b), 135.71 and
134.60 ( COC6H5, ipso in 1a and 1b), 133.71 and 129.63 ( COC6H5, para in 1a and 1b),
128.74 ( COC6H5, ortho in 1b), 128.52 ( COC6H5, meta in 1b), 128.34 ( COC6H5, ortho in 1a),

125.42 ( COC6H5, meta in 1a), 120.04 and 114.39 (=NCH=CHS in 1a and 1b), 90.99
(N,SุCCH= in 1a), 42.65 (N,SุCCH2 in 1b).
DEPT 135 NMR (150 MHz, CDCl3): 142.24, 140.25, 133.85, 129.77, 128.88, 128.66, 128.52,
125.56, 120.18, 114.53, 91.13, 42.78.
(Z)-2-(4,5-dimethylthiazol-2-yl)-1-phenylethenol (3a) and 2-(4,5-dimethyl- thiazol-2-yl)-1-
phenylethanone (3b)
Tautomers (Z)-2-(4,5-dimethylthiazol-2-yl)-1-phenylethenol 3a and 2-(4,5-dimethylthiazol-2-yl)-
1-phenylethanone 3b were synthesized by reacting (Z)-2-(4,5-dimethylthiazol-2-yl)-1-
phenylvinyl benzoate 32 (0.502 g, 1.50 mmol, 1 eq.) in 10 mL of anhydrous MeOH and KOH
(0.168 g, 2.99 mmol, 2 eq.) in 10 mL MeOH by the general procedure used for the synthesis and
purification of equilibrating tautomers of 1. The eluent used for column chromatography over
silica gel was ethyl acetate/hexane = 1:7. Tautomers 3a and 3b (0.308 g, 84.8%) were isolated.
1H and 13C NMR in CDCl3 confirmed that the isolated product consists of equilibrating
tautomers (Z)-2-(4-methylthiazol-2-yl)-1-phenylethenol 3a and 2-(4-methylthiazol-2-yl)-1-
phenylethanone 3b in a 1:1.41 ratio.
Yellow solid; mp = 80-81 C; Rf = 0.44 (ethyl acetate/hexane = 1:6)
IR (neat): 3089, 3055, 3038, 2980, 2918, 1630, 1573, 1555, 1492, 1454, 1268, 1146, 1060, 817,
770, 747, 687, 648 cm-1.
1H NMR (300 MHz, CDCl3): 13.52 (broad OH, 1H), 8.04 (d, J = 7.66 Hz, C6H5 ortho in 3b,
2H), 7.79 (d, J = 7.41 Hz, C6H5 ortho in 3a, 2H), 7.58 (t, J = 7.38 Hz, C6H5 para in 3b, 1H), 7.48
(t, J = 7.57 Hz, C6H5 meta in 3b, 2H), 7.41-7.35 (m, C6H5 meta and para in 3a, 3H), 6.19 (s,
=CH in 3a, 1H), 4.61 (s, CH2 in 3b, 2H), 2.32, 2.31 and 2.30 (s, =NC(CH3)=C(CH3)S and
=NC(CH3)=C(CH3)S in both 3a and 3b, 12H).

The areas of the peaks for 3a and 3b were considered separately since their mole ratio in the
solution was not 1:1. All peaks were first integrated by setting the area of the vinyl proton (=CH)
peak of the enol tautomer 3a at 6.19 ppm at one versus the rest of the resonances for 3a. The area
of the methylene protons ( CH2) of the keto tautomer 3b at 4.61 ppm was set at two versus the
rest of the resonances for 3b. The integration values of each peak and coupling patterns were
used when assigning proton signals for the each tautomer. To obtain the mole ratio between 3a
and 3b in CDCl3, the integrated area of the CH2 at 4.61 ppm was set at two and then the =CH
peak at 6.19 ppm was integrated and found to have an area of 0.71 versus the integrated area of
the methylene proton peak of the keto form. The enol =CH peak corresponds to one proton per
molecule and the keto CH2 peak corresponds to two protons per molecule. Therefore, to calculate
the mole ratio between 3a and 3b, half of the keto CH2 integrated area (1.0) of 3b was divided by
the enol =CH integrated area (0.71). This gave 1:1.41 ratio for 3a:3b.
13C NMR (75 MHz, CDCl3): 194.79 ( CH2CO in 3b), 164.01 (=C(OH) in 3a), 160.45 and
157.33 (N,SุC in both 3a and 3b), 147.50 and 145.00 (=NC(CH3)=C(CH3)S in both 3a and
3b), 135.86 and 135.10 ( COC6H5, ipso in both 3a and 3b), 133.57 and 129.32 ( COC6H5,
para in both 3a and 3b), 128.69 and 128.52 ( COC6H5, ortho in both 3a and 3b), 128.33 (
COC6H5, meta in 3a or 3b), 127.27 (=NC(CH3)=C(CH3)S in 3a or 3b), 125.25 ( COC6H5,
meta in 3a or 3b), 121.56 (=NC(CH3)=C(CH3)S in 3a or 3b), 90.64 (N,SุCCH in 3a), 42.92
(N,SุCCH2 in 3b), 14.52 (=NC(CH3)=C(CH3)S in 3b), 14.24 (=NC(CH3)=C(CH3)S in 3a),
11.23 (=NC(CH3)=C(CH3)S in 3b), 11.14 (=NC(CH3)=C(CH3)S in 3a).
DEPT 135 NMR (150 MHz, CDCl3): 133.68, 129.42, 128.80, 128.44, 125.35, 90.75, 43.02,
14.63, 14.34, 11.34, 11.25.

(Z)-2-(4,5-dimethyloxazol-2-yl)-1-phenylethenol (4a) and 2-(4,5-dimethyl-oxazol-2-yl)-1-
phenylethanone (4b)
Tautomers (Z)-2-(4,5-dimethyloxazol-2-yl)-1-phenylethenol 4a and 2-(4,5-dimethyloxazol-2-yl)-
1- phenylethanone 4b were synthesized by reacting (Z)-2-(4,5-dimethyloxazol-2-yl)-1-
phenylvinyl benzoate (1.6 g, 5.1 mmol, 1 eq.) in 15 mL of anhydrous MeOH and KOH (0.578 g,
10.3 mmol, 2 eq.) in 10 mL MeOH by the general procedure used for the synthesis and
purification of equilibrating tautomers of 1. The eluent used for column chromatography over
silica gel was ethyl acetate/hexane = 1:7. Tautomers 4a and 4b (0.811 g, 73.8%) were isolated.
1H and 13C NMR in CDCl3 confirmed that the isolated product consists of equilibrating
tautomers (Z)-2-(4,5-dimethyloxazol-2-yl)-1-phenylethenol 4a and 2-(4,5-dimethyloxazol-2-yl)-
1- phenylethanone 4b in 1:3.57 ratio.
Dark green oil; Rf = 0.57 (ethyl acetate/hexane = 1:6).
IR (neat): 3059, 2980, 2953, 2924, 2882, 1693, 1633, 1598, 1578, 1532, 1496, 1449, 1293, 1201,
1066, 1012, 756, 713, 688, 639, 618 cm-1.
1H NMR (600 MHz, CDCl3):
OH peak was not seen, 7.94 (d, J = 7.66 Hz, C6H5 ortho in 4b,
2H), 7.71 (d, J = 7.72, C6H5 ortho in 4a 2H), 7.51 (m, C6H5 meta and para in 4a, and C6H5 meta
in 4b, 5H), 7.32 (t, J = 7.56, para in 4b, 1H), 5.91 (s, =CH in 4a, 0.40H), 4.37 (s, CH2 in 4b,
2H), 2.17 (s, =NC(CH3)=C(CH3)S or =NC(CH3)=C(CH3)O in 4a, 3H), 2.14 (s,
=NC(CH3)=C(CH3)O or =NC(CH3)=C(CH3)O in 4b, 3H), 2.03 (s, =NC(CH3)=C(CH3)O or
=NC(CH3)=C(CH3)O in 4a, 3H), 2.02 (s, =NC(CH3)=C(CH3)O or =NC(CH3)=C(CH3)O in
4b, 3H).
The areas of the peaks for 4a and 4b were considered separately since their mole ratio in the
solution was not 1:1. All peaks were first integrated by setting the area of the vinyl proton (=CH)
peak of the enol tautomer 4a at 5.91 ppm at one versus the rest of the resonances for 4a. The area
of the methylene protons ( CH2) of the keto tautomer 4b at 4.37 ppm was set at two versus the

rest of the resonances for 4b. The integration values of each peak and coupling patterns were
used when assigning proton signals for the each tautomer. To obtain the mole ratio between 4a
and 4b in CDCl3, the integrated area of the CH2 at 4.37 ppm was set at two and then the =CH
peak at 5.91 ppm was integrated and found to have an area of 0.28 versus the integrated area of
the methylene proton peak of the keto form. The enol =CH peak corresponds to one proton per
molecule and the keto CH2 peak corresponds to two protons per molecule. Therefore, to calculate
the mole ratio between 4a and 4b, half of the keto CH2 integrated area (1.0) of 4b was divided by
the enol =CH integrated area (0.28). This gave 1:3.57 ratio for 4a:4b.
13C NMR (75 MHz, CDCl3): 193.28 ( CH2CO in 4b), 161.23 (=C(OH) in 4a), 160.92
(N,SุC in 4a), 155.28 (N,SุC in 4b), 143.98 (=NC(CH3)=C(CH3)O in 4b), 140.21
(=NC(CH3)=C(CH3)O in 4a), 135.63
( COC6H5, ipso in 4b), 134.42 ( COC6H5, ipso in 4a), 133.49 ( COC6H5, para in 4b), 130.61
( COC6H5, para in 4a), 129.41 (=NC(CH3)=C(CH3)O in 4b), 128.88 (=NC(CH3)=C(CH3)O
in 4a), 128.57 ( COC6H5, ortho in 4b), 128.36 ( COC6H5, meta in 4b), 128.22 ( COC6H5,
ortho in 4a), 125.08 ( COC6H5, meta in 4a), 84.01 (N,OุCCH= in 4a), 38.81 (N,OุCCH2 in
4b), 10.88 (=NC(CH3)=C(CH3)O in 4b), 10.73 (=NC(CH3)=C(CH3)O in 4a), 9.75
(=NC(CH3)=C(CH3)O in 4b), 9.63 (=NC(CH3)=C(CH3)O in 4a).
DEPT 135 NMR (150 MHz, CDCl3): 133.71, 129.62, 128.78, 128.58, 128.42, 125.30, 84.23,
39.04, 11.05, 10.95, 9.97, 9.86.
(Z)-2-(benzo[d]thiazol-2-yl)-1-phenylethenol (5a) and 2-(benzo[d]thiazol-2-yl)-1-
phenylethanone (5b)
Tautomers (Z)-2-(benzo[d]thiazol-2-yl)-1-phenylethenol 5a and 2-(benzo[d]thiazol-2-yl)-1-
phenylethanone 5b were synthesized by reacting (Z)-2-(benzo[d]thiazol-2-yl)-1-phenylvinyl
benzoate 34 (1.008 g, 2.82 mmol, 1 eq.) in 15 mL of anhydrous MeOH and KOH (0.316 g, 5.63

mmol, 2 eq.) in 10 mL MeOH by the general procedure used for the synthesis and purification of
equilibrating tautomers of 1b. The eluent used for column chromatography over silica gel was
ethyl acetate/hexane = 1:5. Tautomers 5a and 5b (0.516 g, 72.8%) were isolated. 1H and 13C
NMR in CDCl3 confirmed that the isolated product consists of equilibrating tautomers 5a and 5b
in a 1.63:1 ratio.
Yellowish green solid; mp = 111-112 C; Rf = 0.64 (ethyl acetate/hexane = 1:5).
IR (neat): 3057, 2922, 1610, 1596, 1573, 1494, 1473, 1436, 1378, 1264, 1249, 1136, 1057, 751,
729, 687, 668 cm-1.
1H NMR (600 MHz, CDCl3): 13.91 (broad OH, 1H), 8.07 (d, J = 7.68 Hz,
C6H5 ortho in 5b, 2H), 7.99 (d, J = 8.13 Hz, aromatic CH in the benzothiazole ring of 5b, 1H),
7.85-7.87 (m, C6H5 ortho in 5a and aromatic CH in the benzothiazole ring of 5b, 3H), 7.80 (d, J
= 8.10 Hz, aromatic CH in the benzothiazole ring of 5a, 1H), 7.76 (d, J = 7.93 Hz, aromatic CH
in the benzothiazole ring of 5a, 1H), 7.58 (dd, J = 8.13 and 7.91 Hz, aromatic CH in
benzothiazole ring in 5b, 1H), 7.48 (dd, J = 7.68 and 7.53 Hz, C6H5 meta in 5b, 2H), 7.41-7.46
(m, C6H5 meta in 5a and CH in the benzothiazole ring of 5a and 5b, 5H), 7.36 (t, J = 7.53 Hz,
C6H5 para in 5b, 1H), 7.27 (t, J = 7.53 Hz, C6H5 para in 5a, 1H), 6.35 (s, =CH in 5a, 1H),
4.81 (s, CH2 in 5b, 2H).
The areas of the peaks for 5a and 5b were considered separately since their mole ratio in the
solution was not 1:1. All peaks were first integrated by setting the area of the vinyl proton (=CH)
peak of the enol tautomer 5a at 6.35 ppm at one versus the rest of the resonances for 5a. The area
of the methylene protons ( CH2) of the keto tautomer 5b at 4.81 ppm was set at two versus the
rest of the resonances for 5b. The integration values of each peak and coupling patterns were
used when assigning proton signals for the each tautomer. To obtain the mole ratio between 5a
and 5b in CDCl3, the integrated area of the CH2 at 4.81 ppm was set at two and then the =CH

peak at 6.35 ppm was integrated and found to have an area of 1.63 versus the integrated area of
the methylene proton peak of the keto form. The enol =CH peak corresponds to one proton per
molecule and the keto CH2 peak corresponds to two protons per molecule. Therefore, to
calculate the mole ratio between 5a and 5b, half of the keto CH2 integrated area (1.0) of 5b was
used with respect to the enol =CH integrated area (1.63). This gave 1:1.63 ratio for 5a:5b.
13C NMR (150 MHz, CDCl3): 194.05 ( CH2CO in 5b), 168.07 (N,SุC in 5b), 165.46
(N,SุC in 5a), 163.44 (=C(OH) in 5a), 152.68 (C next to N in the benzothiazole rings in 5b),
150.38 (C next to N in the benzothiazole rings in 5a), 135.88 and 135.78 (C next to S in the
benzothiazole rings and COC6H5, ipso in 5b),
134.74 ( COC6H5, ipso in 5a), 133.82 ( COC6H5, para 5b), 131.37 (C next to S in the
benzothiazole rings of 5a), 130.28 ( COC6H5, para 5a), 128.81 and 128.64
( COC6H5, meta and ortho in 5b, 4C), 128.48 ( COC6H5, meta in 5a, 2C), 126.46 and 125.96
(aromatic CH in the benzothiazole ring of 5a and 5b, 2C), 125.89 ( COC6H5, ortho in 5a, 2C),
125.05, 124.11, 122.85, 121.51, 121.37 and 119.95 (aromatic CH in the benzothiazole ring of 5a
and 5b, 6C), 90.83 (N,SุCCH= in 5a), 43.81 (N,SุCCH2 in 5b).
DEPT 135 NMR (150 MHz, CDCl3): 133.91, 130.38, 128.90, 128.73, 128.58, 126.56, 126.06,
125.98, 125.15, 124.20, 122.95, 121.60, 121.46, 120.04, 90.92, 43.91.
(Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenol (6a) and 2-(benzo[d]oxazol-2-yl)-1-
phenylethanone (6b)
Tautomers (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylethenol 6a and 2-(benzo[d]oxazol-2-yl)-1-
phenylethanone 6b were synthesized by reacting (Z)-2-(benzo[d]oxazol-2-yl)-1-phenylvinyl
benzoate 35 (0.844 g, 2.47 mmol, 1 eq.) in 15 mL of anhydrous MeOH and KOH (0.28 g, 5.2
mmol, 2.1 eq.) in 10 mL MeOH by the general procedure used for the synthesis and purification
of equilibrating tautomers of 1. The eluent used for column chromatography over silica gel was

ethyl acetate/hexane = 1:5. Tautomers 6a and 6b (0.541 g, 92.2%) were isolated. 1H and 13C
NMR in CDCl3 confirmed that the isolated product consists of equilibrating tautomers (Z)-2-
(benzo[d]oxazol-2-yl)-1-phenylethenol 6a and 2-(benzo[d]oxazol-2-yl)-1-phenylethanone 6b in
a 1.06:1 ratio.
Greenish white solid; mp = 87-89 C; Rf = 0.64 (ethyl acetate/hexane = 1:5).
IR (neat): 3065, 3032, 3044, 2979, 1625, 1576, 1530, 1453, 1277, 1250, 1164, 1064, 850, 792,
743, 762, 702, 685 cm-1.
1H NMR (600 MHz, CDCl3): 12.62 (broad OH, 1H), 8.05 (d, J = 7.74 Hz,
C6H5 ortho , 2H), 7.88 (m, aromatic CH, 2H), 7.72 (m, J = 4.21 Hz, aromatic CH, 1H), 7.61 (m,
aromatic CH, 2H), 7.52-7.45 (m, aromatic CH, 7H), 7.34-7.31 (m, J = 6.64 Hz, aromatic CH,
3H), 7.28 (t, J = 7.66 Hz, aromatic CH, 1H), 6.21 (s, =CH in 6a, 1H), 4.64 (s, CH2 in 6b,
2H).
The areas of the peaks for 6a and 6b were considered separately since their mole ratio in the
solution was not 1:1. All peaks were first integrated by setting the area of the vinyl proton (=CH)
peak of the enol tautomer 6a at 6.21 ppm at one versus the rest of the resonances for 6a. The area
of the methylene protons ( CH2) of the keto tautomer 6b at 4.64 ppm was set at two versus the
rest of the resonances for 6b. The integration values of each peak and coupling patterns were
used when assigning proton signals for the each tautomer. To obtain the mole ratio between 6a
and 6b in CDCl3, the integrated area of the CH2 at 4.64 ppm was set at two and then the =CH
peak at 6.21 ppm was integrated and found to have an area of 1.06 versus the integrated area of
the methylene proton peak of the keto form. The enol =CH peak corresponds to one proton per
molecule and the keto CH2 peak corresponds to two protons per molecule. Therefore, to
calculate the mole ratio between 6a and 6b, half of the keto CH2 integrated area (1.0) of 6b was
used respect to the enol =CH integrated area (1.06). This gave 1.06:1 ratio for 6a:6b.

13C NMR (150 MHz, CDCl3): 192.38 ( CH2CO in 6b), 166.19 (=C(OH) in 6a), 165.68
(N,OุC in 6b), 160.41 (N,OุC in 6a), 151.24 (C next to O in benzoxazole rings of 6b),
148.69 (C next to O in benzoxazole rings of 6a), 141.26 (C next to N in benzoxazole rings of
6b), 139.85 (C next to N in benzoxazole rings of 6a), 135.66 ( COC6H5, ipso in 6b), 134.03
( COC6H5, ipso in 6a), 133.71
( COC6H5, para in 6b, 130.56 ( COC6H5, meta in 6a), 128.85 ( COC6H5, ortho in 6b, 128.59
( COC6H5, meta in 6b, 128.53 ( COC6H5, meta in 6a), 125.82
( COC6H5, ortho in 6a), 124.98 (aromatic CH on the benzoxazole ring in 6b), 124.61, 124.32
(aromatic CH on the benzoxazole ring in 6b), 124.08 (aromatic CH on the benzoxazole ring in
6a), 119.95 (aromatic CH on the benzoxazole ring in 6b), 117.85 (aromatic CH on the
benzoxazole ring in 6a), 110.61 (aromatic CH on the benzoxazole ring in 6b), 110.19 (aromatic
CH on the benzoxazole ring in 6a), 83.66 (N,OุCCH= in 6a), 39.56 (N,OุCCH2 in 6b).
DEPT 135 NMR (150 MHz, CDCl3): 133.99, 130.64, 128.93, 128.67, 128.61, 125.90, 125.07,
124.69, 124.16, 120.03, 117.93, 110.69, 110.27, 83.74, 39.64.
8-Benzoyl-6,6-dimethyl-6H-thiazolo[3,2-a]pyridine-5,7-dione (36)
2,2-Dimethylmalonyl dichloride (0.53 g, 3.2 mmol, 1.5 eq.) in CH3CN (15 mL) was added
dropwise over a period of 10 min to a stirred solution of the tautomers 1a,b (0.414 g, 2.04 mmol,
1 eq.) and triethylamine (0.726 g, 7.17 mmol, 3.5 eq.) in CH3CN (30 mL) at room temperature
under nitrogen. This solution was refluxed (82 C) for 5 h under nitrogen and then CH3CN was
removed by rotary evaporation. The residue was dissolved in dichloromethane (30 mL), washed
with 10% aqueous sodium bicarbonate (30 mL), followed by water (2 × 30 mL) and dried over
anhydrous sodium sulfate. Sodium sulfate was removed by filtration. After removal of
dichloromethane by rotary evaporation, the crude product was purified by column

chromatography over silica gel (ethyl acetate/hexane = 1:2). 1a,b eluted first followed by 105
and then compound 251. The un-reacted starting tautomers 1a,b (0.065 g, 15%), the vinyl
benzoate ester 105 (0.056 g, 18%; mp = 105-106 C) and the 5,6-ring-fused compound 36
(0.216 g, 35.4%) were isolated.
This reaction was repeated as follows. The tautomer 1a,b (0.582 g, 2.86 mmol, 1 eq.) and Et3N
(1.01 g, 9.98 mmol, 3.49 eq.) were dissolved in CH3CN (30 mL). Then 2,2-dimethylmalonyl
dichloride (0.779 g, 4.8 mmol, 1.68 eq.) in CH3CN (15 mL) was added dropwise over a period of
20 min to the stirred solution of 1a,b and Et3N and refluxed for 7 h. The general procedure
mentioned above was followed for the purification and isolation of products. 10% (0.045 g) of
31 and 65% (0.56 g) of 36 were isolated.
A control reaction was carried out in the absence of 2,2-dimethylmalonyl dichloride to see
whether the 2,2-dimethylmalonyl dichloride is a necessary reagent for the formation of 31 in
refluxing CH3CN. A solution of the tautomers 1a,b (0.205 g, 1.01 mmol, 1 eq.) and Et3N (0.357
g, 3.5 mmol, 3.5 eq.) in CH3CN (35 mL) was refluxed. The spot for 31 did not appear on the
TLC even after refluxing for 12 h. The reaction solution was cooled to room temperature, 2,2-
dimethylmalonyl dichloride (0.265 g, 1.54 mmol, 1.54 eq.) was added dropwise and then the
reaction solution was refluxed for another 8 h. The vinyl ester 31 (0.023 g, 16%) and the 5,6-
ring-fused compound 36 (0.056 g, 19%) were isolated after following the above mentioned
general procedure for purification and isolation.
Yellow solid; mp = 213-214 °C.; Rf = 0.53 (EtOAc-hexane = 2:3).
IR (neat): 3155, 3110, 3095, 2974, 2927, 1741, 1637, 1593, 1568, 1523, 1475, 1386, 1331, 1158,
1096, 914, 874, 803, 768, 734, 710, 676 cm-1.

1H NMR (600 MHz, CDCl3):
(d, J = 4.60 Hz, =NCH CHS , 1H), 7.50 (d, J = 7.65 Hz
C6H5 ortho, 2H), 7.46 (t, J = 7.39 Hz, C6H5 para, 1H), 7.39 (dd, J = 7.65 and 7.39 Hz, C6H5
meta, 2H), 6.77 (d, J = 4.60 Hz, =NCH CHS , 1H), 1.59 (s, CO2C(CH3)2CO2 , 6H).
13C NMR (600 MHz, CDCl3):
COC6H5), 189.64 ( C(CH3)2CO), 172.70 (>NCO ),
167.77 (N,S>C=), 139.96 ( COC6H5, ipso), 130.83 (>NCH=CHS ), 127.68 ( COC6H5, ortho
and para, 3C), 122.82 ( COC6H5, meta), 112.99 (>NCH=CHS ), 106.63 (=C(COC6H5) ), 53.76
( C(CH3)2 ), 23.82 ( C(CH3)2 ).
DEPT 135 NMR (150 MHz, CDCl3): 130.88, 127.73, 122.88, 113.04, 23.87.
HRMS (ESI, [M+H]+): calcd for C16H14NO3S: 300.0694; found: 300.0692.
8-Benzoyl-6,6-diethyl-6H-thiazolo[3,2-a]pyridine-5,7-dione (37)
2,2-Diethylmalonyl dichloride (0.531 g, 2.75 mmol, 1.2 equiv.) in CH3CN (10 mL) was added
dropwise over a period of 20 min to a stirred solution of the tautomers 1a,b (0.479 g, 2.36 mmol,
1 equiv.) and Et3N (0.815 g, 9.51 mmol, 3.3 equiv.) in CH3CN (25 mL). This solution was
refluxed for 5 h. The general procedure mentioned above was used for the purification and
isolation of products. The title compound 37 was isolated in 52% (0.402 g) along with the
starting tautomers 1a,b in 10% (0.047 g) yield.
Yellow solid; mp = 185-186 °C; Rf = 0.67 (EtOAc-hexane = 2:3).
IR (neat): 3161, 3124, 3061, 2962, 2935, 2876, 1729, 1681, 1633, 1601, 1475, 1385, 1331, 1204,
1163, 927, 876, 841, 821, 796, 699, 676 cm-1.
1H NMR (600 MHz, CDCl3):
(d, J = 4.59 Hz, =NCH CHS , 1H), 7.51 (d, J = 7.64 Hz
C6H5 ortho, 2H), 7.47 (t, J = 7.32 Hz, C6H5 para, 1H), 7.40 (dd, J = 7.64 and 7.32 Hz, C6H5
meta, 2H), 6.77 d, J = 4.59 Hz, =NCH CHS , 1H), 2.13 (qt, Jgem = 15.0 Hz, Jvis = 7.42 Hz,

CH2CH3, 2H), 2.01 (qt, Jgem = 15.0 Hz, Jvis = 7.42 Hz, CH2CH3, 2H), 0.87 (t, J = 7.42 Hz,
CH2CH3, 6H).
13C NMR (600 MHz, CDCl3):
COC6H5), 188.93 ( C(CH3)2CO), 172.16 (>NCO ),
168.61 (N,S>C=), 140.21 ( COC6H5, ipso), 130.80 ( COC6H5, para), 127.76 ( COC6H5, ortho),
127.63 ( COC6H5, meta), 122.53 (>NCH=CHS ), 113.03 (>NCH=CHS ), 109.06
(=C(COC6H5) ), 32.37 ( CH2CH3 , 2H), 9.54 ( CH2CH3 , 2H).
DEPT 135 NMR (150 MHz, CDCl3): 130.85, 127.81, 127.69, 122.58, 113.09, 32.43, 9.60.
HRMS (ESI, [M+H]+): calcd for C18H18NO3S: 328.1007; found: 328.0992.
10-Benzoyl-7,8-dihydropyrano[2,3-d]thiazolo[3,2-a] pyridin-5(6H)-one (40)
Cyclobutane-1,1-dicarbonyl dichloride (0.631 g, 3.49 mmol, 1.5 equiv.) in CH3CN (10
mL) was added dropwise over a period of 15 min at room temperature to a stirred solution of the
tautomers 1a,b (0.465 g, 2.29 mmol, 1 equiv.) and Et3N (0.83 g, 8.2 mmol, 3.6 equiv.) in CH3CN
(25 mL). This solution was refluxed 5 h. The general procedure mentioned above for the
purification and isolation of product 36 was followed. The spot corresponding to the staring
tautomers 1a,b was not observed on TLC of the products mixture. The title compound 40 was
isolated in 13% (0.093 g). EtOAc-hexane = 1:1 was used as the eluent for the column
chromatography over silica. Three other liquid fractions were collected through column in
addition to the fraction that corresponds to 40 (Eluent used was EtOAc-hexane = 1:1). These
three fractions eluted before the product. Fraction 1 (0.217 g) eluted first followed by fraction 2
(0.066 g), and then fraction 3 (0.353 g). The 1H NMR spectra of these three fractions were not
clear enough to analyze and identify the structures. These 1H NMR spectra are given in Figures
S1-S3.

This reaction was repeated employing an inverse addition by adding a solution of the tautomers
1a,b (0.423 g, 2.08 mmol, 1 equiv.) and Et3N (0.71 g, 7.02 mmol, 3.4 equiv.) in CH3CN (25 mL)
to a solution of cyclobutane-1,1-dicarbonyl dichloride (0.57 g, 3.15 mmol, 1.5 equiv.) in CH3CN
(10 mL) dropwise over a period of 20 min at room temperature. Then this solution was refluxed
for 5 h. There was no TLC spot detected for 1a,b on the TLC. After following the general work
up procedure 40 was isolated in 34% yield. Two other liquid fractions were also isolated which
eluted before the product (Eluting solvent was ethyl acetate/hexane = 1:1). The fraction 1 (0.102
g) isolated first, followed by fraction 2 (0.207 g). The 1H NMR spectra of fractions 1 and 2 are
appeared in Figure S4 and S5.
White crystalline solid; mp = 226-227 °C; Rf = 0.50 (ethyl acetate/hexane = 3:1).
IR (neat): 3149, 3089, 3066, 2979, 2937, 2904, 1645, 1597, 1530, 1489, 1333, 1308, 1266, 1183,
1158, 1058, 961, 905, 848, 733, 697 cm-1.
1H NMR (600 MHz, CDCl3): 8.24 (d, J = 4.48 Hz, >NCH=CHS , 1H), 7.57 (d, J = 7.69 Hz
C6H5 ortho, 2H), 7.46 (t, J = 7.29 Hz, C6H5 para, 1H), 7.40 (dd, J = 7.69 and 7.29 Hz, C6H5
meta, 2H), 7.04 (d, J = 4.48 Hz, >NCH=CHS , 1H), 3.94 (t, J = 5.13 Hz, OCH2CH2CH2C=,
2H), 2.68 (t, J = 6.46 Hz, OCH2CH2CH2C=, 2H), 1.95 (tt, J = 5.13 and 6.46 Hz,
OCH2CH2CH2C=, 2H).
13C NMR (150 MHz, CDCl3): 190.52 ( COC6H5), 161.37 ( NCO ), 159.08 (=COCH2 ),
153.04 (N,S>C=), 141.02 ( COC6H5, ipso), 130.62 ( COC6H5, para), 127.90 ( COC6H5, ortho),
127.38 ( COC6H5, meta), 123.51 (>NCH=CHS ), 114.00 (>NCH=CHS ) 104.05 (>NCOC=),
99.89 (=C(COC6H5) ), 66.61 ( OCH2CH2CH2C=), 20.69 ( OCH2CH2CH2C=), 19.67
( OCH2CH2CH2C=).

DEPT 135 NMR (150 MHz, CDCl3): 130.74, 128.02, 127.49, 123.62, 114.11, 66.72, 20.80,
19.28.
HRMS (ESI, [M+H]+): calcd for C17H14NO3S: 312.0694; found: 312.0677.
Single crystals of 40 were grown for X-ray crystallography by the vapor diffusion method.
Hexane was diffused into a solution of compound 40 dissolved in chloroform.
8-Benzoyl-2,3,6,6-tetramethyl-6H-thiazolo[3,2-a]pyridine-5,7-dione (38) and bis((Z)-2-(4,5-
dimethylthiazol-2-yl)-1-phenylvinyl) 2,2-dimethylmalonate (41)
2-Dimethylmalonyl dichloride (0.53 g, 3.1 mmol, 1.53 equiv.) in CH3CN (10 mL) was added
dropwise over a period of 20 min to a stirred solution of the tautomers 3a,b (0.465g, 2.01 mmol,
1 equiv.) and Et3N (0.721 g, 7.13 mmol, 3.55 equiv.) in CH3CN (25 mL). This solution was
refluxed for 6 h. There was no spot on TLC corresponding to the starting material. Three spots
with Rf values 0.64, 0.50 and 0.35 (EtOAc-hexane = 1:2) were detected. The general procedure
mentioned above in synthesis of 36 was employed for the purification and isolation of products.
EtOAc:hexane 1:2 was used as the eluting solvent for the column chromatography. The first
fraction (Rf = 0.64; EtOAc-hexane = 1:2) was isolated in 0.099 g. It was unidentified and its 1H
NMR is given in Figure S6. Product 38 (0.221 g, 34%) eluted next, followed by bis-vinyl ester
41 (0.058 g, 10%).
An inverse addition was performed by adding a solution of the tautomers 3a,b (0.463 g, 2.0
mmol, 1 equiv.) and Et3N (0.712 g, 7.04 mmol, 3.52 equiv.) in CH3CN (25 mL) to a solution of
2,2-dimethylmalonyl dichloride (0.523 g, 3.03 mmol, 1.51 equiv.) in CH3CN (10 mL) dropwise
over a period of 20 min. This solution was refluxed for 6 h. Three spots were observed (Rf =
0.67, 0.52, 0.36; EtOAc-hexane = 1:2) on TLC and no spot was seen for 3a,b. Compound 38
(0.322 g, 49%) was isolated using EtOAc-hexane 1:2 as the eluting solvent for the column

chromatography after the general work up procedure. The bis-vinyl ester 41 was also isolated in
5% (0.016 g) yield. The fraction corresponding to Rf = 0.67 has not been collected.
Yellow crystalline solid; mp = 173-174 °C; Rf = 0.50 (ethyl acetate/hexane = 1:2).
IR (neat): 3062, 3022, 2986, 2940, 1741, 1688, 1649, 1589, 1564, 1453, 1386, 1372, 1356, 1220,
1184, 1082, 983, 910, 922, 842, 802, 768, 735, 708, 634 cm-1.
1H NMR (600 MHz, CDCl3): 7.46 (d, J = 7.43 Hz, C6H5 ortho, 2H), 7.42 (t, J = 7.36 Hz,
C6H5 para, 1H), 7.36 (dd, J = 7.43 and 7.36 Hz, C6H5 meta, 2H), 2.44 (s,
>NC(CH3)=C(CH3)S or >NC(CH3)=C(CH3)S , 3H), 2.17 (s, >NC(CH3)=C(CH3)S or
>NC(CH3)=C(CH3)S , 3H), 1.53 (s, C(CH3)2 , 6H).
13C NMR (150 MHz, CDCl3): 190.81 ( COC6H5), 188.79 ( NCOC(CH3)2CO ), 174.50
( NCO ), 168.24 (N,S>C=), 140.48 ( COC6H5, ipso), 130.89 (>NC(CH3)=C(CH3)S ), 130.21
( COC6H5, para), 127.39 ( COC6H5, ortho), 127.35 ( COC6H5, meta), 118.80
(>NC(CH3)=C(CH3)S ), 105.52 (=C(COC6H5) ), 54.70 ( C(CH3)2C ), 23.31 ( C(CH3)2C ),
13.93 (>NC(CH3)=C(CH3)S or >NC(CH3)=C(CH3)S ), 10.68 (>NC(CH3)=C(CH3)S or
>NC(CH3)=C(CH3)S ).
DPET 135 NMR (150 MHz, CDCl3): 130.47, 127.65, 127.62, 23.57, 14.20, 10.95.
HRMS (ESI, [M+H]+): calcd for C18H18NO3S: 328.1007; found: 328.0988.
Bis[(Z)-2-(4,5-dimethylthiazol-2-yl)-1-phenylvinyl] 2,2-dimethylmalonate (41)
Pale yellow solid; mp = 170-172°C; Rf = 0.35 (EtOAc-hexane = 1:2).
IR (neat): 3057, 2981, 2951, 2922, 2858, 1768, 1745, 1632, 1536, 1248, 1129, 1082, 1021, 760,
690 cm-1.
1H NMR (600 MHz, CDCl3): .54 (d, J = 7.41 Hz, C6H5 ortho, 4H), 7.26-7.23 (m,

C6H5 meta and para, 6H), 7.00 (s, CH=C(C6H5)O , 2H), 2.34 (s, >NC(CH3)=C(CH3)S , 6H),
2.32 (s, >NC(CH3)=C(CH3)S , 6H), 1.99 (s, C(CH3)2 , 6H).
13C NMR (150 MHz, CDCl3):
CO2C(C6H5)=, 156.12 (N,S>C=), 148.97
(=C(C6H5)O or >NC(CH3)=C(CH3)S ), 148.32 ( CH=C(C6H5)O or >NC(CH3)=C(CH3)S ),
134.11 ( COC6H5, ipso), 129.26 ( COC6H5, para), 128.62
( COC6H5, ortho), 127.73 (>NC(CH3)=C(CH3)S ), 125.23 ( COC6H5, meta), 111.42
( CH=C(C6H5)O ), 51.16 ( C(CH3)2 ), 23.63 ( C(CH3)2 ),14.61 (>NC(CH3)=C(CH3)S or
>NC(CH3)=C(CH3)S ), 11.29 (>NC(CH3)=C(CH3)S or >NC(CH3)=C(CH3)S ).
DEPT 135 NMR (150 MHz, CDCl3): 129.32, 128.69, 125.30, 111.49, 23.70, 14.68, 11.37.
HRMS (ESI, [M+H]+): calcd for C31H31N2O4S2: 559.1725; found: 559.1659.
8-Benzoyl-2,3,6,6-tetramethyl-6H-oxazolo[3,2-a]pyridine-5,7-dione (39)
2,2-Dimethylmalonyl dichloride (0.301 g, 1.74 mmol, 1.38 equiv.) in CH3CN (10 mL)
was added dropwise over a period of 20 min to a stirred solution of the tautomers 4a,b (0.272,
1.26 mmol, 1 equiv.) and Et3N (0.432 g, 4.27 mmol, 3.39 equiv.) in CH3CN (25 mL). This
solution was refluxed for 7 h. The spot corresponding to the starting tautomers 4a,b was not
detected by TLC. About five to six spots were observed on the TLC analysis of the reaction
products. The general procedure mentioned above was employed for the purification and
isolation of products. The separation of each of them was not easy. EtOAc-hexane 1:2 was used
as the eluting solvent for the column chromatography. Fractions corresponding to all spots were
not isolated. Only three fractions have been collected. The 5,6-ring-fused compound 39 was
isolated in 27% yield (0.106 g) as the first fraction. The isolated fraction 2 was a brown sticky
oil. This compound was identified as the bis-vinyl ester 42 (0.059g, 18%) based on the 1H NMR

spectrum. The 1H NMR spectrum of fraction 3 (0.08 g), which eluted last was unidentified and
its 1H NMR spectrum is given Figure S7.
An inverse addition version of this reaction was also performed by adding solution of the
tautomers 4a,b (0.47g, 2.2 mmol, 1 equiv.) and Et3N (0.781 g, 7.72 mmol, 3.51 equiv.) in
CH3CN (30 mL) to a solution of 2,2-dimethylmalonyl dichloride (0.541 g, 3.14 mmol, 1.43
equiv.) in CH3CN (20 mL) dropwise over a period of 30 min. This solution was then refluxed for
7 h. Several spots were seen on the TLC of the reaction products as in the previous case. Some of
these spots were very close. Therefore, separate fractions were not collected corresponding to all
these spots. EtOAc-hexane 1:3 and then 1:1 were used as the eluting solvent for the column
chromatography. Only four fractions were collected. Fraction 1 (0.089 g) followed by fraction 2
(0.045 g) were collected as the first two fractions. Their 1H NMR spectra are given in Figures S8
and S9, respectively. Compound 39 (0.237 g, 35%) was isolated as the third fraction (fraction 3).
Fraction 4 (0.056 g) was collected as the last fraction and it was also unidentified. The 1H NMR
spectra of fraction 4 is given in Figure S10. The 1H NMR spectra of the isolated unidentified
fractions 1, 2 and 4 do not match up with the spectrum corresponding to bis-vinyl ester 42.
8-Benzoyl-2,3-dimethyl-6H-oxazolo[3,2-a]pyrimidine-5,7-dione (39)
Yellow crystalline solid; mp = 176-178 °C; Rf = 0.36 (EtOAc-hexane = 1:1).
IR (neat): 3053, 2997, 2960, 1739, 1715, 1652, 1599, 1586, 1415, 1258, 1186, 1014, 986, 914,
821, 803, 770, 749, 712, 691, 651 cm-1.
1H NMR (600 MHz, CDCl3): .70 (d, J = 7.7 Hz, C6H5 ortho, 2H), 7.50 (t, J = 7.21 Hz,
C6H5 para, 1H), 7.40 (dd, J = 7.7 Hz and 7.21 Hz, C6H5 meta, 2H), 2.39 (s,
>NC(CH3)=C(CH3)O , 3H), 2.18 (s, >NC(CH3)=C(CH3)O , 3H), 1.54 (s, C(CH3)2 , 6H).

13C NMR (150 MHz, CDCl3):
COC6H5), 190.79 ( NCOC(CH3)2CO ), 173.04 (
NCO ), 164.25 (N,S>C=), 140.88 ( COC6H5, ipso), 139.29 (>NC(CH3)=C(CH3)O ), 132.19 (
COC6H5, para), 128.68 ( COC6H5, ortho), 127.97
( COC6H5, meta), 117.54 (>NC(CH3)=C(CH3)O ), 95.93 (=C(COC6H5) ), 53.63
( C(CH3)2 ), 24.34 ( C(CH3)2 ), 9.69 (>NC(CH3)=C(CH3)O or >NC(CH3)=C(CH3)O ), 9.49
(>NC(CH3)=C(CH3)O or >NC(CH3)=C(CH3)O ).
DEPT 135 NMR (150 MHz, CDCl3): 132.26, 128.74, 128.03, 24.41, 9.76, 9.56.
HRMS (ESI, [M+H]+): calcd for C18H18NO4: 312.1236; found: 312.1219.
Single crystals of 39 were obtained for X-ray crystallography by the vapor diffusion method.
Hexane was diffused into a solution of compound 39 dissolved in chloroform.
Bis[(Z)-2-(4,5-dimethyloxazol-2-yl)-1-phenylvinyl] 2,2-dimethylmalonate (42)
Brown sticky oil Rf = 0.49 (EtOAc-hexane = 1:1).
1H NMR (600 MHz, CDCl3): .58 (d, J = 7.60 Hz, C6H5 ortho, 4H), 7.28-7.23 (m,
C6H5 meta and para, 6H), 6.74 (s, CH=C(C6H5)O , 2H), 2.21 (s, >NC(CH3)=C(CH3)S , 6H),
2.08 (s, >NC(CH3)=C(CH3)S , 6H), 1.98 (s, C(CH3)2 , 6H).
4-Benzoyl-2,2-dimethyl-1H-benzo[4,5]thiazolo[3,2-a] pyridine-1,3(2H)-dione (45) and Bis[(Z)-2-
(benzo[d]thiazol-2-yl)-1-phenylvinyl] 2,2-dimethylmalonate (46)
2,2-Dimethylmalonyl dichloride (0.293 g, 1.77 mmol, 1.49 equiv.) in CH3CN (10 mL) was
added dropwise over a period of 20 min to a stirred solution of the tautomers 5a,b (0.302 g, 1.19
mmol, 1 equiv.) and Et3N (0.429 g, 4.24 mmol, 3.56 equiv.) in CH3CN (25 mL). This solution
was refluxed for 8 h. The spot for 5a,b was not observed on TLC. The general purification

procedure mentioned in the synthesis of 36 was employed for the purification and isolation of
products. EtOAc-hexane 1:3 was used as the eluting solvent for the column chromatography.
Compound 45 (0.182 g, 44%) eluted first, followed by compound 46 (0.026 g, 7%). In addition
to fractions corresponding to 45 and 46, two more fractions have been collected, which had
complex 1H NMR spectra (Figures S11 and S12). These two fractions were collected before 45
and 46, in the order of fraction 1 (0.061 g) and fraction 2 (0.049 g).
An inverse addition reaction was also performed by adding a solution of the tautomers 5a,b
(0.507 g, 2.00 mmol, 1 equiv.) and Et3N (0.715 g, 7.07 mmol, 3.54 equiv.) in CH3CN (30 mL)
to a solution of 2,2-dimethylmalonyl dichloride (0.524 g, 3.04 mmol, 1.52 equiv.) in CH3CN (15
mL) dropwise over a period of 30 min. This solution was refluxed for 8 h and the general work
up procedure was followed. The eluting solvent used for the column chromatography was
EtOAc-hexane 1:3. Compound 45 was isolated in 62% yield (0.435 g). There were several other
spots including a very pale spot for compound 46, but these were not isolated.
4-Benzoyl-2,2-dimethyl-1H-benzo[4,5]thiazolo[3,2-a] pyridine-1,3(2H)-dione (45)
White cotton like solid; mp = 238-239 °C; Rf = 0.51 (EtOAc-hexane = 1:3).
IR (neat): 3126, 3080, 3028, 3000, 2947, 1732, 1657, 1609, 1471, 1385, 1356, 1212, 1121, 936,
910, 760, 736, 700, 593 cm-1.
1H NMR (600 MHz, CDCl3):
(d, J = 8.34 Hz, aromatic H, 1H), 7.68 (d, J = 7.65 Hz,
aromatic H, 1H), 7.52-7.39 (m, C6H5 ortho, para, meta and aromatic H, 7H), 1.64 (s, C(CH3)2 ,
6H).

13C NMR (150 MHz, CDCl3):
COC6H5), 190.16 ( NCOC(CH3)2CO ), 174.44 (
NCO ), 168.27 (N,S>C=), 139.96 (>NCุCS or COC6H5 ipso), 136.09 (>NCุCS or
COC6H5 ipso), 131.12 ( COC6H5 para), 128.06 (aromatic C), 127.78 ( COC6H5, ortho), 127.67
( COC6H5 meta), 127.14 (>NCุCS ), 126.80 (aromatic C), 122.02 (aromatic C), 118.02
(aromatic C), 107.58 (=C(COC6H5) ), 54.58 ( C(CH3)2C ), 23.80 ( C(CH3)2C ).
DEPT 135 (150 MHz, CDCl3): 131.20, 128.14, 127.86, 127.75, 126.88, 122.10, 118.10, 23.88.
HRMS (ESI, [M+H]+): calcd for C20H16NO3S: 350.0851; found: 350.0819.
Bis((Z)-2-(benzo[d]thiazol-2-yl)-1-phenylvinyl) 2,2-di-methylmalonate (46)
Off-white solid; mp = 139-141 °C; Rf = 0.54 (EtOAc-hexane = 1:1).
IR (neat): 3059, 2993, 2942, 1760, 1739, 1577, 1253, 1209, 1073, 755, 727, 689 cm-1.
1H NMR (600 MHz, CDCl3):
03 (d, J = 8.09 Hz, aromatic, 2H), 7.82 (d, J = 7.91 Hz,
aromatic, 2H), 7.63 (d, J = 6.94 Hz, C6H5 ortho, 4H), 7.48 (t, J = 7.56 Hz C6H5 para, 2H), 7.37
(t, J = 7.51 Hz, aromatic, 2H), 7.28-7.25 (m, C6H5 meta and aromatic H, 6H), 7.17 (s, =CH ,
2H), 2.14 (s, C(CH3)2 , 6H).
13C NMR (150 MHz, CDCl3): 169.52 CO2C(C6H5)=), 160.72 (N,S>C=), 153.18
(=C(C6H5)O or >NCุCS ), 151.84 ( CH=C(C6H5)O or >NCุCS ), 134.97 (>NCุCS or
COC6H5 ipso), 133.71 (>NCุCS or COC6H5 ipso), 130.07
( COC6H5, para), 128.76 ( COC6H5, ortho), 126.44 (aromatic C), 125.68 ( COC6H5, meta),
125.47 (aromatic C), 123.09 (aromatic C), 121.42 (aromatic C), 111.26
( CH=C(C6H5)O ), 51.44 ( C(CH3)2 ), 23.80 ( C(CH3)2 ).

DEPT 135 NMR (150 MHz, CDCl3): 130.13, 128.82, 126.50, 125.74, 125.52, 123.14, 121.47,
111.31, 23.85.
HRMS (ESI, [M+H]+): calcd for C35H27N2O4S2: 603.1412; found: 603.1339.
4-Benzoyl-2,2-dimethyl-1H-benzo[4,5]oxazolo[3,2-a] pyridine-1,3(2H)-dione (47)
2,2-Dimethylmalonyl dichloride (0.373 g, 2.16 mmol, 1.54 equiv.) in CH3CN (10 mL) was
added dropwise over a period of 20 min to a stirred solution of the tautomers 6a,b (0.332 g, 1.40
mmol, 1 equiv.) and Et3N (0.509 g, 5.03 mmol, 3.59 equiv.) in CH3CN (25 mL). This solution
was refluxed for 9 h. There was no spot on the TLC analysis corresponding to the starting
material. The general procedure mentioned in the procedure for the synthesis of 36 was
employed for the purification and isolation of products. The TLC of the product mixture had
several spots that were very close. Isolation of fractions corresponding to all these spots was not
attempted. EtOAc-hexane 1:3 was used as the eluting solvent for column chromatography. The
first collected fraction (brown, oil: 0.076 g) was unidentified and its 1H NMR spectrum is given
in Figure S13. The next fraction collected, corresponding to the major spot, was 47. This was
isolated in 31% yield (0.146 g).
Next, an inverse addition reaction was carried out. A solution of the tautomers 6a,b (0.476 g,
2.01 mmol, 1 equiv.) and Et3N (0.722 g, 7.14 mmol, 3.55 equiv.) in CH3CN (30 mL) was added
dropwise to a solution of 2,2-dimethylmalonyl dichloride (0.526 g, 3.05 mmol, 1.52 equiv.) in
CH3CN (15 mL) over a period of 30 min. This solution was then refluxed for 9 h. The major spot
on the TLC analysis of this product mixture corresponded to 47. Compound 47 (0.244 g, 35%)
was isolated using EtOAc-hexane 1:3 as the eluting solvent for the column chromatography after
completing the general work up procedure. Several other spots, which were not very well
separated, were seen on TLC. Their further separations were not attempted.

This reaction was repeated by the inverse addition of 5a,b (0.211 g, 0.89 mmol, 1 equiv.) and
Et3N (0.316 g, 3.12 mmol, 3.55 equiv.) to a solution of 2,2-dimethylmalonyl dichloride (0.307 g,
1.78 mmol, 2 equiv.), followed by refluxing for 9 h. The general work up procedure was
followed. The 1H NMR of the first fraction isolated (brown oil; 0.034 g) from this reaction is
same as that of the first fraction mentioned above corresponding to the brown oil (Figure S13).
The 5,6-ring-fused compound 47 was isolated in 42% yield (0.124 g) after column separation.
White solid; mp = 249-250 °C; Rf = 0.38 (EtOAc-hexane = 1:3).
IR (neat): 3110, 3095, 3060, 3027, 3001, 2933, 1730, 1644, 1569, 1467, 1396, 1352, 1307, 1213,
1159, 11245, 1008, 965, 910, 827, 761, 743, 708, 693, 654, 607 cm-1.
1H NMR (600 MHz, CDCl3):
(d, J = 7.94 Hz, aromatic, 1H), 7.80 (d, J = 7.79 Hz, C6H5
ortho, 2H), 7.56 (t, J = 7.36 Hz, C6H5 para, 1H), 7.44 (dd, J = 7.79 and 7.36 Hz, C6H5 meta, 2H),
7.39-7.34 (m, aromatic H, 3H), 1.64 (s, C(CH3)2 , 6H).
13C NMR (150 MHz, CDCl3):
COC6H5), 190.07 ( NCOC(CH3)2CO ), 172.16
( NCO ), 163.38 (N,O>C=), 146.88 (>NCุCO or COC6H5, ipso), 138.38 (>NCุCO or
COC6H5, ipso), 132.98 ( COC6H5, para), 128.98 ( COC6H5, ortho), 128.29 ( COC6H5, meta),
126.66 (aromatic C), 126.10 (aromatic C), 125.90 (>NCุCO ), 115.41 (aromatic C), 111.10
(aromatic C), 97.12 (=C(COC6H5) ), 53.51 ( C(CH3)2 ), 24.42 ( C(CH3)2 ).
DEPT 135 (150 MHz, CDCl3): 133.01, 129.02, 128.33, 126.14, 115.42, 111.15, 24.46. HRMS
(ESI, [M+H]+): calcd for C20H16NO4: 334.1079; found: 334.1054.
8-Benzoyl-6H-thiazolo[3,2-f]pyrimidine-5,7-dione (53)
N-Chlorocarbonyl isocyanate (0.335 g, 3.18 mmol, 1.4 equiv.) in THF (15 mL) was added
dropwise to a stirred solution of the tautomers 1a,b (0.461 g, 2.26 mmol, 1 equiv.) and
triethylamine (0.574 g, 5.67 mmol, 2.51 equiv.) in THF (20 mL) at room temperature under