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Scheme 3. A proposed mechanism for the cyclization.
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Scheme 4. Another proposed mechanism.
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11. General procedure for the palladium-catalyzed cycliza-
tion: The appropriate allylated b-bromo-vinylaldehyde,
Pd(OAc)2 (10 mol %), PPh3 (0.25 equiv), HCOONa
(1 equiv) and DMF were placed in a two neck round
bottom flask. After degassing with N2 it was heated to
80 °C for 8 h. After cooling, the reaction mixture was
diluted with cold water and extracted with diethyl ether,
and dried (Na2SO4). The solvent was evaporated under
reduced pressure, and was isolated by column chroma-
tography.
Figure 1. ORTEP view of the structure 7b.
12. Authors are thankful to the referee for proposing the
alternative mechanism.
Acknowledgements
13. Selected data for 7b: IR (KBr) 1679, 1628 cmꢀ1; 1H NMR
(CDCl3, 200 MHz) d 1.56 (d, 3H, J ¼ 7 Hz), 2.56, 2.65 (dd,
1H, Jcis ¼ 2:0 Hz, Jgem ¼ 18:0 Hz), 3.23, 3.32 (dd, 1H,
Jtrans ¼ 6:16 Hz, Jgem ¼ 18:0 Hz), 3.60–3.68 (m, 1H), 7.55–
7.69 (m, 2H), 7.82–8.02 (m, 4H); 13C NMR (CDCl3,
50 MHz) d 20.87, 31.49, 50.36, 124.63, 126.14, 127.58,
127.64, 128.15, 129.47, 130.60, 131.19, 133.11, 133.74,
142.79, 181.14, 200.17. Anal. Calcd for C16H12O: C, 87.27;
H, 5.45. Found: C, 87.54; H, 5.36. MS (EI, 70 eV) m=z 220
(Mþ).
Financial support from DST (New Delhi) and CSIR
(New Delhi) (for fellowship to S.M.) is gratefully
acknowledged. We also thank Dr. K. Biradha, IIT––
Kharagpur, India for the crystal structure.
References and Notes
1. Tsuji, J. Transition Metal Reagents and Catalysts: Innova-
tions in Organic synthesis; Wiley: New York, 2002.
14. Biradha, K.; Mal, S.; Ray, D.; Ray, J. Unpublished
data.