3
regioslectivity in the case of nitrone 1g may be explained in
terms of differential population of rotamers of a key intermediate
(18a and 18b) involved in the nitrone-acetylene reaction (Figure
1). Structure of different nitrones examined by us is collected in
Chart 1. The structure and yield of quinoline products are
summarized in Chart 2 and that of 3(2H)-furanones isolated in
certain cases as a minor product are collected in Chart 3.
#Dedicated to Professor Jonathan S. Lindsey on his sixtieth
birthday.
Acknowledgments
RN is thankful to CSIR for the award of a Senior Research
Fellowship. SR and JPR acknowledge UGC for financial
assistance in the form of minor research projects (1622-MRP/14-
15/KLCA025/UGC-SWRO to SR and 1551-MRP/14-
15/KLCA009/UGC-SWRO to JPR). DST (PURSE and FIST
grants), UGC-SAP, and Kerala Government provided additional
financial support. SAIF (STIC) CUSAT provided spectral and
analytical data.
Supplementary data
Figure 1. Rotamers of intermediate 18 involved in the
reaction between 1g and DBA
Supplementary data (synthetic procedures, compound
characterization, CCDC numbers of the compounds 6b and 8a,
1H and 13C NMR spectra for the compounds 6a-h, 16a-e and 8b-
d) associated with this article can be found in the Science Direct
publication website.
References
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Chart 1. Nitrones used for quinoline synthesis
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Chart 2. Structure and yield of quinolones
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Chart 3. Structure and isolated yield of 3(2H)-furanones
In summary, we have developed a simple yet flexible, metal
free synthesis of substituted quinolines under mild conditions. By
recycling fluorenone generated in the hydrolysis step, we could
enhance the atom efficiency of quinoline synthesis protocol
developed by us. We could incorporate substituents specifically
at predetermined positions of quinoline product. Our method
provides easy access to benzo[h]quinolines such as 6h and 16e.
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and 7-substituted quinolines remains elusive.
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