Synthetic studies on benzo-fused five-membered N/O heterocycles
LE3 .A278 2012
Master of Science
Numerous benzo-fused five-membered N/O heterocycles serve as skeletal frameworks in many commercially important compounds and natural products. This thesis deals with three types for benzo-fused five-membered heterocycles: indoles, isoindoles and benzofurans. In Chapter 1 of this thesis, we report a simple synthesis of mono-, di- and triacetylated derivatives of indoles starting from indolin-2-ones in two steps. First, the indolin-2-one moieties were triacetylated by acetic anhydride in the presence of DMAP. Subsequently, enzyme-catalyzed mono-deacetylation yields 1,3-diacetyl-2-hydroxyindoles, whereas use of mild basic conditions results in double deacetylation producing 3-acetyl-2-hydroxyindoles. In Chapter 2, synthesis of 5-substituted 6,6a-dihydroisoindolo[2,1a]quinolin-11(5H)-ones via [4+2] imino Diels-Alder cyclization from N-aryl-3-hydroxy-isoindolinones and N-vinyl lactams under Lewis acid-catalyzed anhydrous conditions is reported. Non-cyclized products were formed when N-(2-substituted-aryl)-3-hydroxy-isoindolinones were used with N-vinylpyrrolidone under identical conditions. In Chapter 3, a green methodology to synthesize 2,2-dialkyl-2,3-dihydrobenzofurans from cheaply and abundantly available phenols and 2,2-dialkylacetaldehydes under microwave conditions is reported. This one-step conversion has several advantages such as very short reaction time, solvent-free conditions and use of an economical catalyst.
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