Convenient synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines

Article abstract of DOI:10.1080/00397910903398668

A convenient general synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b] quinolines using the Wittig reaction is described. The o-nitrobenzaldehydes (1a-d) on reaction with phosphorane 2 provided (E)-ethyl-α-(2,2- dimethylprop-2-ene)-2-nitrocinnamates (3a-d) in excellent yields, which on cyclization with polyphosphoric acid followed by reductive cyclization using Fe/HCl afforded dihydropyranoquinolines (5a-d). Alternatively, the pyranoquinolines 5a-d were also synthesised from esters 3a-d by employing domino reductive cyclization in a single step. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910903398668

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Convenient Synthesis of 2,2-
Dimethyl-3,4-dihydro-2H-pyrano[2,3-
b]quinolines
Sonia B. Parsekar a , Chandan P. Amonkar a , Peruninakulath S.
Parameswaran b & Santosh G. Tilve a
a Department of Chemistry, Goa University, Goa, India
b National Institute of Oceanography, Dona Paula, Goa, India
Published online: 04 Oct 2010.
To cite this article: Sonia B. Parsekar , Chandan P. Amonkar , Peruninakulath S. Parameswaran
& Santosh G. Tilve (2010): Convenient Synthesis of 2,2-Dimethyl-3,4-dihydro-2H-pyrano[2,3-
b]quinolines, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 40:21, 3251-3258
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Synthetic Communications1, 40: 3251–3258, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903398668
CONVENIENT SYNTHESIS OF 2,2-DIMETHYL-
3,4-DIHYDRO-2H-PYRANO[2,3-b]QUINOLINES
Sonia B. Parsekar,1 Chandan P. Amonkar,1
Peruninakulath S. Parameswaran,2 and Santosh G. Tilve1
1Department of Chemistry, Goa University, Goa, India
2National Institute of Oceanography, Dona Paula, Goa, India
A convenient general synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines
using the Wittig reaction is described. The o-nitrobenzaldehydes (1a–d) on reaction with
phosphorane 2 provided (E)-ethyl-a-(2,2-dimethylprop-2-ene)-2-nitrocinnamates (3a–d)
in excellent yields, which on cyclization with polyphosphoric acid followed by reductive
cyclization using Fe=HCl afforded dihydropyranoquinolines (5a–d). Alternatively, the pyr-
anoquinolines 5a–d were also synthesised from esters 3a–d by employing domino reductive
cyclization in a single step.
Keywords: Domino reaction; lactones; pyranoquinoline; reductive cyclization; Wittig reaction
Quinoline and its annulated derivatives are important compounds for synthetic and
biological chemists.[1] These alkaloids are useful as antimalarial, antihypertensive,
anti-inflammatory, antiasthamatic, antibacterial, and tyrosine kinase inhibiting
agents.[2] Significant numbers of quinoline alkaloids have 2,2-dimethylpyran units
attached to the quinoline rings. These pyranoquinoline alkaloids display a wide
range of biological activities.[3] Balfourodendron riedelianum (Rutaceae), a small
Brazilian tree, is a rich source of pyrano[2,3-b]quinolines and furo[2,3-b]quinolines.[4]
The extract of this plant is used in folk medicine for the treatment of gastrointestinal
ailments.[5] Flindersin, ribalinine, helietidine, and dutadrupine are some examples of
quinoline alkaloids containing the pyran unit (Fig. 1).
Because of their potent biological activities, numerous methods have been
developed for these alkaloids.[6]
RESULTS AND DISCUSSION
In continuation of our studies exploiting phosphorous chemistry,[7] we report
herein a convenient general synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-
b]quinolines (5a–d). Wittig reaction of the phosphorane[8] (2) with o-nitrobenzaldehydes
Received July 30, 2009.
Address correspondence to Santosh G. Tilve, Department of Chemistry, Goa University, Goa 403
206, India. E-mail: stilve@unigoa.ac.in
3251

3252
S. B. PARSEKAR ET AL.
Figure 1. Natural pyranoquinolines.
(1a–d) gave exclusively ethyl (2E)-5-methyl-2[(2-nitrophenyl)methylidene]hex-4-
enoates (3a–d). The unsaturated esters (3a–d) were further cyclized to d-(E)-lactones
(4a–d) using polyphosphoric acid (PPA). No isomerization of the E-lactone to
Z-lactone was observed during this acid-mediated cyclization.
The lactones (4a–d) were then subjected to reductive cyclization[9] using Fe and
conc. HCl to furnish corresponding dihydropyranoquinolines (5a–d), and reduction
of nitro to amino, isomerization of E to Z-lactone, and cyclization took place in one
pot in a domino fashion[10] (Scheme 1). Furthermore, to make our synthesis more
concise, an alternate method was attempted, wherein Wittig product (3a–d) was
directly subjected to reductive cyclization by Fe and conc. HCl to get the
corresponding dihydropyranoquinolines (5a–d) without isolating the lactone
intermediates (4a–d). However, the yield of isolated product (5a–d) during this one
Scheme 1. Synthesis of dihydropyranoquinolines.

2,2-DIMETHYL-3,4-DIHYDRO-2H-PYRANO[2,3-b]QUINOLINES
3253
Table 1. Yields in the synthesis of dihydropyranoquinolines
Yield (%)
Entry
R1
R2
3
4
5
5 from 3
19
a
b
c
H
OR
H
H
90
=
82 (R COOEt)
85
=
95 (R COOEt)
54
=
85 (R OH)
=
36 (R OH)
OCH3
OCH3
66
68
80
82
76
83
25
33
d
-OCH2O-
pot concurrent lactonization=isomerization=reductive cyclization was somewhat less
than the overall yield from the two-step strategy mentioned previously. The results
are summarized in Table 1.
In conclusion, we have developed a new and effective methodology for the
synthesis of 2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines using phosphor-
ane chemistry. The noteworthy step is the one-pot reductive cyclization to yield
directly the annulated tricyclic ring system.
EXPERIMENTAL
Thin-layer chromatography (TLC) was performed on silica gel G (13% CaSO4
as binder). Column chromatography was performed on silica gel (60–120 mesh).
Infrared (IR) spectra were recorded on a Shimadzuu Fourier transform (FT)–IR
1
spectrophotometer (KBr pellets). H NMR (300 MHz) and 13C NMR (75 MHz)
were recorded on a Bruker instrument. The multiplicities of carbon signals were
obtained from distortionless enhancement by polarization transfer (DEPT) experi-
ments. Chemical shift (ppm) are relative to the internal standard Me4Si (0 ppm).
High-resolution mass spectra (HRMS) were recorded on a MicroMass ES-QTOF.
General Procedure for the Preparation of Ethyl (2E)-5-Methyl-
2[(2-nitrophenyl)methylidene]hex-4-enoates (3a–d)
A solution of aldehyde (1 mmol) 1a–d in chloroform (10 mL) was refluxed with
phosphorane[6] 2 (1 mmol) for 3 h. The solvent was removed under reduced pressure
to give a residue, which was purified by column chromatography (silica gel,
hexane-EtOAc, 9:1) to give pure 3a–d as viscous liquids.
Data
Ethyl (2E)-5-Methyl-2[(2-nitrophenyl)methylidene]hex-4-enoate (3a). Yield:
1
90%; thick viscous yellow liquid; IR (KBr): 1713 cmꢀ1 (C O). H NMR (300 MHz,
=
CDCl3): d ¼ 1.35 (t, J ¼ 7.2 Hz, 3H), 1.42 (s, 3H), 1.64 (s, 3H), 2.98 (d, J ¼ 6.3 Hz,
2H), 4.30 (q, J ¼ 7.2 Hz, 2H), 5.03 (m, 1H), 7.37 (d, J ¼ 7.5 Hz, 1H), 7.51 (t,
J ¼ 7.5 Hz, 1H), 7.65 (t, J ¼ 7.8 Hz, 1H), 7.9 (s, 1H), 8.13 (d, J ¼ 8.1 Hz, 1H). 13C
NMR (75 MHz, CDCl3): d ¼ 14.23 (CH3), 17.64 (CH3), 25.66 (CH3), 27.06 (CH2),
61.04 (OCH2), 120.97 (CH), 124.72 (CH), 128.90 (CH), 131.18 (CH), 132.07 (C),

3254
S. B. PARSEKAR ET AL.
=
132.81 (C), 133.28 (CH), 133.91 (C), 135.59 (CH), 147.71 (C), 167.28 (C O). GC=
MS: m=z 289 [Mþ].
Ethyl (2E)-2-({5-[(Ethoxycarbonyl)oxy]-2-nitrophenyl}methylidene)-5-
methylhex-4-enoate (3b). Yield: 82%; thick viscous yellow liquid; IR (KBr):
1
1722, 1770 cmꢀ1 (C O). H NMR (300 MHz, CDCl3): d ¼ 1.26–1.43 (m, 6H), 1.64
=
(s, 6H), 2.93 (d, J ¼ 6.6 Hz, 2H), 4.19–4.33 (m, 4H), 4.95 (br s, 1H), 7.15 (d,
J ¼ 2.4 Hz, 1H), 8.14 (d, J ¼ 9.0 Hz, 1H), 7.29 (dd, J ¼ 9.0, 2.4 Hz, 1H), 7.79 (s,
1H). 13C NMR (75 MHz, CDCl3): d ¼ 14.11 (CH3), 14.20 (CH3), 17.54 (CH3),
25.61 (CH3), 26.99 (CH2), 61.11 (OCH2), 65.56 (OCH2), 120.65 (CH), 121.23
(CH), 123.52 (CH), 126.56 (CH), 133 (C), 134.11 (C), 134.40 (C), 13þ4.72 (CH),
=
144.71 (C), 152.32 (C), 154.06 (C), 167.03 (C O). GC=MS: m=z 377 [M ].
Ethyl (2E)-2-[(4,5-Dimethoxy-2-nitrophenyl)methylidene]-5-methylhex-
4-enoate (3c). Yield: 66%; thick viscous yellow liquid. IR (KBr): 1709 cmꢀ1
(C O). 1H NMR (300 MHz, CDCl3): d ¼ 1.37 (t, J ¼ 7.2 Hz, 3H), 1.49 (s, 3H),
=
1.67 (s, 3H), 3.00 (d, J ¼ 6.0 Hz, 2H), 3.92 (s, 3H), 4.00 (s, 3H), 4.31 (q, J ¼ 7.2 Hz,
2H), 5.1 (m, 1H), 6.77 (s, 1H), 7.75 (s, 1H), 7.94 (s, 1H). 13C NMR (75 MHz, CDCl3):
d ¼ 14.24 (CH3), 17.85 (CH3), 25.62 (CH3), 27.28 (CH2), 56.33 (OCH3), 56.40
(OCH3), 60.99 (OCH2), 107.70 (CH), 112.42 (CH), 121.77 (CH), 126.66 (C),
132.75 (C), 132.83 (C), 136.82 (CH), 140.15 (C), 148.55 (C), 152.97 (C), 167.41
þ
=
(C O). GC=MS: m=z 349 [M ].
Ethyl (2E)-5-Methyl-2-[(6-nitro-1,3-benzodioxol-5-yl)methylidene]hex-
4-enoate (3d). Yield: 68%; thick viscous yellow liquid. IR (KBr): 1713 cmꢀ1
1
=
(C O). H NMR (300 MHz, CDCl3): d ¼ 1.35 (t, J ¼ 7.2 Hz, 3H), 1.51 (s, 3H), 1.67
(s, 3H), 3.00 (d, J ¼ 6.6 Hz, 2H), 4.29 (q, J ¼ 7.2 Hz, 2H), 5.06 (m, 1H), 6.17 (s, 2H),
6.74 (s, 1H), 7.65 (s, 1H), 7.83 (s, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 14.21
(CH3), 17.68 (CH3), 25.66 (CH3), 27.15 (CH2), 60.99 (OCH2), 103.20 (CH2), 105.50
(CH), 109.74 (CH), 121.02 (CH), 128.74 (C), 132.74 (C), 133.05 (C), 136.22 (CH),
þ
=
141.87 (C), 147.78 (C), 151.77 (C), 167.30 (C O). GC=MS: m=z 333 [M ].
General Procedure for the Preparation of (3E)-6,6-Dimethyl-3-
[(2-nitrophenyl)methylidene]tetrahydro-2H-pyran-2-ones (4a–d)
Compounds 3a–d (1 mmol) were added to the stirred solution of polyphospho-
ric acid (2 mL). The reaction mixture was warmed on water bath for 5 min. Chilled
water (15 mL) was added to the reaction mixture, and it was subsequently extracted
with diethyl ether (3 ꢁ 10 mL). The organic layer was washed with saturated
NaHCO3 solution (2 ꢁ 30 mL) and dried over anhydrous Na2SO4. The solvent was
removed under reduced pressure, and the residue was purified by column chromato-
graphy (silica gel, hexane–EtOAc, 9:1) to give pure 4a–d.
Data
(3E)-6,6-Dimethyl-3-[(2-nitrophenyl)methylidene]tetrahydro-2H-pyran-2-
ꢀ1
1
one (4a). Yield: 85%; white solid; mp 96–98 ꢂC. IR (KBr): 1692 cm (C O). H
NMR (300 MHz, CDCl3): d ¼ 1.46 (s, 6H), 1.85 (t, J ¼ 6.9 Hz, 2H), 2.56 (dt,
=

2,2-DIMETHYL-3,4-DIHYDRO-2H-PYRANO[2,3-b]QUINOLINES
3255
J ¼ 6.9, 2.4 Hz, 2H), 7.39 (d, J ¼ 7.5 Hz, 1H), 7.55 (t, J ¼ 7.5 Hz, 1H), 7.69 (t,
J ¼ 7.5 Hz, 1H), 8.11 (br s, 1H), 8.17 (d, J ¼ 8.1 Hz, 1H). 13C NMR (75 MHz,
CDCl3): d ¼ 21.66 (CH2), 27.96 (2 ꢁ CH3), 33.13 (CH2), 80.94 (C), 125 (CH),
127.04 (C), 129.41 (CH), 130.66 (CH), 131.21 (C),þ133.43 (CH), 138.15 (CH),
=
147.72 (C), 165.79 (C O). HRMS: m=z [M þ Na] calcd. for C14H15NNaO4:
284.0899; found: 284.0893.
3-[(E)-(6,6-Dimethyl-2-oxodihydro-2H-pyran-3(4H)-ylidene)methyl]-4-
nitrophenyl Ethyl Carbonate (4b). Yield: 95%; white solid; mp 104–106 ꢂC. IR
1
(KBr): 1774, 1717 cmꢀ1 (C O). H NMR (300 MHz, CDCl3): d ¼ 1.34 (t, J ¼ 7.2 Hz,
=
Hz, 3H), 1.40 (s, 6H), 1.78 (t, J ¼ 6.9 Hz, 2H), 2.53 (dt, J ¼ 6.9, 2.4 Hz, 2H), 4.30 (q,
J ¼ 7.2 Hz, 2H), 7.18 (d, J ¼ 2.4 Hz, 1H), 7.32 (dd, J ¼ 9.0, 2.4 Hz, 1H), 8.03 (br s,
1H), 8.17 (d, J ¼ 9.0 Hz, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 14.11 (CH3), 21.60
(CH2), 27.95 (2 ꢁ CH3), 33.08 (CH2), 65.68 (CH2), 81.00 (C), 121.56 (CH), 123.08
(CH), 126.89 (CH), 127.63 (C), 133.22 (C), 137.22 (þCH), 144.66 (C), 152.31 (C),
=
154.10 (C), 165.48 (C O). HRMS: m=z [M þ Na] calcd. for C17H19NNaO7:
372.1059; found: 372.1059.
(3E)-3-[(4,5-Dimethoxy-2-nitrophenyl)methylidene]-6,6-dimethyltetra-
hydro-2H-pyran-2-one (4c). Yield: 80%; yellow solid; mp 181–182 ꢂC. IR (KBr):
1
1692 cmꢀ1 (C O). H NMR (300 MHz, CDCl3): d ¼ 1.46 (s, 6H), 1.85 (t, J ¼ 6.9 Hz,
=
Hz, 2H), 2.55 (dt, J ¼ 6.6, 2.1 Hz, 2H), 3.98 (s, 3H), 4.00 (s, 3H), 6.73 (s, 1H), 7.76 (s,
1H), 8.11 (br s, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 21.75 (CH2), 27.98 (2 ꢁ CH3),
33.20 (CH2), 56.47 (OCH3), 56.62 (OCH3), 80.83 (C), 107.97 (CH), 111.63 (CH),
125.75 (C), 126.16 (C), 139.1þ7 (CH), 140.33 (C), 148.88 (C), 153.14 (C), 166.02
=
(C O). HRMS: m=z [M þ Na] calcd. for C16H19NNaO6: 344.1110; found 344.1113.
(3E)-6,6-Dimethyl-3-[(6-nitro-1,3-benzodioxol-5-yl)methylidene]tetra-
hydro-2H-pyran-2-one (4d). Yield: 82%; yellow solid; mp 176–177 ꢂC. IR (KBr):
1
1697 cmꢀ1(C O). H NMR (300 MHz, CDCl3): d ¼ 1.45 (s, 6H), 1.85 (t, J ¼ 6.9 Hz,
=
Hz, 2H), 2.56 (dt, J ¼ 6.9, 2.4 Hz, 2H), 6.18 (s, 2H), 6.73 (s, 1H), 7.67 (s, 1H), 8.04 (br
s, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 21.65 (CH2), 27.94 (2 ꢁ CH3), 33.11 (CH2),
80.83 (C), 103.38 (OCH2O), 105.79 (CH), 109.00 (CH), 126.14 (C), 127.84 (C),
=
þ
138.91 (CH), 142 (C), 148.13 (C), 151.94 (C), 165.9 (C O). HRMS: m=z [M þ Na]
calcd. for C15H15NNaO6: 328.0797; found 328.0800.
General Procedure for the Preparation of
2,2-Dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinolines (5a–d)
Concentrated HCl (8 mL) was added to a magnetically stirred mixture of esters
3a–d or 4a–d (1 mmol) and Fe powder (15 mmol). The reaction mixture was allowed to
stir for 15 min and was subsequently refluxed on a water bath. After completion of the
reaction (the progress of the reaction was monitored by thin-layer chromatography,
TLC), the reaction mixture was filtered, and the residue was washed with water
(3 ꢁ 5 mL). This combined filtrate washed with diethyl ether (2 ꢁ 10 mL) and filtered
on celite. The filtrate was basified with solid NaOH pellets (liquid ammonia was used
to basify compound 3b and 4b), and the compound was subsequently extracted in
diethyl ether (3 ꢁ 15 mL). The combined organic extracts were dried over anhydrous

3256
S. B. PARSEKAR ET AL.
Na2SO4. The solvent was removed under reduced pressure, and the residue was pur-
ified by column chromatography (silica gel, hexane–EtOAc, 8:2) to give pure 5a–d.
Data
2,2-Dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinoline (5a). Yield: 19%
(from 3), 54% (from 4); white solid; mp 103–105 ꢂC. IR (KBr): 1622, 1562, 1492,
1
1415 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 1.50 (s, 6H), 1.96 (t, J ¼ 6.6 Hz, 2H),
3.04 (t, J ¼ 6.3 Hz, 2H), 7.36 (t, J ¼ 7.8, 7.2 Hz, 1H), 7.58 (t, J ¼ 8.1, 7.2 Hz, 1H),
7.68 (d, J ¼ 7.5 Hz, 1H), 7.85 (d, J ¼ 8.7 Hz, 1H), 7.88 (s, 1H). 13C NMR
(75 MHz, CDCl3): d ¼ 22.62 (CH2), 27.36 (2 ꢁ CH3), 32.41 (CH2), 77.08 (C),
117.66 (C), 123.88 (CH), 125.19 (C), 126.56 (CH), 127.22 (CH), 129.02 (CH),
137.51 (CH), 146.42 (C), 159.72 (C). HRMS: m=z [M þ Na]þ calcd. for
C14H15NNaO: 236.1051; found: 236.1049.
2,2-Dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinoline-7-ol
(5b). Yield:
36% (from 3), 85% (from 4); white solid; mp 223–225 ꢂC. IR (KBr): 3300 (OH),
1
1612, 1517, 1434, 1367 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 1.41 (s, 6H), 1.87
(t, J ¼ 6.9 Hz, 2H), 2.93 (t, J ¼ 6.9 Hz, 2H), 5.11 (br s, 1H), 6.96 (d, J ¼ 2.7 Hz,
1H), 7.13 (dd, J ¼ 9.0, 2.7 Hz, 1H), 7.67 (s, 1H), 7.69 (d, J ¼ 9.0 Hz, 1H). 13C
NMR (75 MHz, CDCl3): d ¼ 22.59 (CH2), 27.28 (2 ꢁ CH3), 32.39 (CH2), 70.19
(C), 108.46 (CH), 118.06 (CH), 120.69 (CH), 125.83 (CH), 128.52 (C), 136.16 (C),
141.62 (C), 152.02 (C), 158.20 (C). HRMS: m=z [M þ Na]þ calcd. for C14H15NNaO2:
252.1; found: 252.0999.
7,8-Dimethoxy-2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quinoline (5c).
Yield: 25% (from 3), 76% (from 4); white solid; mp 156–158 ꢂC. IR (KBr): 1612,
1496, 1458, 1381 cmꢀ1
.
1H NMR (300 MHz, CDCl3): d ¼ 1.47 (s, 6H), 1.93 (t,
J ¼ 6.6 Hz, 2H), 2.97 (t, J ¼ 6.6 Hz, 2H), 3.98 (s, 3H), 3.99 (s, 3H), 6.95 (s, 1H),
7.2 (s, 1H), 7.7 (s, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 22.43 (CH2), 27.28
(2 ꢁ CH3), 32.51 (CH2), 55.87 (2 ꢁ CH3), 76.53 (C), 104.69 (CH), 106.62 (CH),
114.85 (C), 119.92 (C), 136 (CH), 143.05 (C), 147.81 (C), 152.07 (C), 158.66 (C).
HRMS: m=z [M þ Na]þ calcd. for C16H19NNaO3: 296.1263; found: 296.1263.
7,8-Methylenedioxy-2,2-dimethyl-3,4-dihydro-2H-pyrano[2,3-b]quino-
line (5d). Yield: 33% (from 3), 83% (from 4); white solid; mp 177–179 ꢂC. IR (KBr):
1
1620, 1480, 1465, 1388 cmꢀ1. H NMR (300 MHz, CDCl3): d ¼ 1.44 (s, 6H), 1.89 (t,
J ¼ 6.6 Hz, 2H), 2.92 (t, J ¼ 6.6 Hz, 2H), 6.02 (s, 2H), 6.91 (s, 1H), 7.15 (s, 1H), 7.65
(s, 1H). 13C NMR (75 MHz, CDCl3): d ¼ 22.32 (CH2), 27.26 (2 ꢁ CH3), 32.44 (CH2),
76.65 (C), 101.26 (CH2), 102.08 (CH), 104.40 (CH), 114.78 (C), 121.10 (C), 136.57
(CH), 144.24 (C), 145.83 (C), 150.21 (C), 158.60 (C). HRMS: m=z [M þ Na]þ calcd.
for C15H15NNaO3: 280.0950; found: 280.0958.
ACKNOWLEDGMENTS
The authors thank the University Grants Commission, New Delhi, for finan-
cial assistance, the National Institute of Oceanography, Goa, for spectral analysis,
and the Department of Organic Chemistry, IISC, Bangalore, for HRMS.

2,2-DIMETHYL-3,4-DIHYDRO-2H-PYRANO[2,3-b]QUINOLINES
3257
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