Heterocycies pyrroles

A fundamental chemical tactic in the synthetic manipulation of heterocycies by organic chemists is the reduction of the heterocyclic ring. This chapter will review advances in the partial and complete reduction of pyrroles, furans, thiophenes and their benzo analogs, indoles, benzo[Z>]furans and benzo[Z>]thio-phenes. As appropriate, coverage will include the reduction of those benzo analogs of lesser interest isoindole, carbazole, benzo[c]furan (isobenzofuran), dibenzofuran and dibenzothiophene. 

A heterocycle is a compound with a ring that has more than one kind of atom. Nitrogen, oxygen, and sulfur are often found along with carbon in heterocyclic rings. Saturated heterocyclic amines, ethers, and sulfides usually have the same chemistry as their open-chain analogs, but unsaturated heterocycies such as pyrrole, furan, and thiophene are aromatic. All three are unusually stable, and all three undergo aromatic substitution on reaction with electrophiles. 

For a basic discussion of tautomerism of pyrrolic heterocycies, the reader is encouraged to consult the first edition <84CHEC-I(3)155>. 

The purpose of this monograph is to provide a comprehensive review of the de novo syntheses of 3-pyrroHn-2-ones that have been reported through the end of 2014. 3-PyrroUn-2-one (5H-pyrrol-2-one) (1) and 4-pyrroUn-2-one (3H-pyrrol-2-one) (3) are tautomers of 2-hydroxypyrrole (2) (Scheme 1). 3-Pyrrolin-2-ones have also been referred to as 1,5-dihydro-2H-pyrrol-2-ones, pyrrol-2-ones, yl ctams, or butyrolactams. Some early synthetic reports represented these heterocycies as 2-hydroxypyrroles (1932MI1, 1937LAC265, 1942MI1, 1943LAC144). Later, NMR analysis showed that the lactam tautomers were actually present, 6 4.0—4.2 for the methylene of parent 1 and 8 2.9—3.2 for the methylene of parent 3... 

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