Heterocycies 7- ring

Ring Synthesis by Transformation of Other Heterocyciic Rings 8.06.10.1 Three-Membered Rings... 

Ring Synthesis Ciassified by Formation of the Second Heterocyciic Ring... 

Compounds with one heteroatom in eaoh heterocyciic ring... 

This extensive study of the opening of three-membered heterocyciic rings came from Huisgen s group in Munich [J. Chem. Soc., Chem. Commun, 1971, 1187, 1188, 1190, and 1192). 

Rees, C. W., Smithen, C. E. The mechanism of heterocyciic ring expansions, ii. Reaction of methylindoles with halocarbenes. J. Chem. 

X = 0, NH, S benzo[c]heterocycies aromaticity is iost in the heterocyciic ring but enhanced in the benzenoid ring... 

We can now proceed. Indoie attacks the unsaturated ketone in Michaei fashion because the conditions are acidic, we protonate the ketone. The product is an enoi, so that is tautomerized to the ketone. This gives the not isoiated intermediate. The next step is ring ciosure, and we have the iminium system of the heterocycie as eiectrophiie. The nucieophiie shouid be distinguishabie as the a-position of the ketone, an enoiate anion equivaient. Under acidic conditions, we cannot have an enoiate anion, so we must empioy the enol. This means a second tautomerization step. Ring ciosure foiiows you may recognize it as equivaient to a Mannich reaction attack of an enoi onto an iminium cation. Loss of a proton and the job is done. 

Ring Strain in Cycioaikanes and their Heterocyciic Counterparts... 

Simultaneous Synthesis of Both Rings from Non-heterocyciic Compounds... 

Syntheses of the Pyrimidine Ring from Other Heterocycies... 

Synthesis of heterocycies, by ring closures with carbon monoxide ... 

Combination of a C-S Unit with a C-C-C Unit. 4 Ring Synthesis by Formation of Three Bonds. 5 Ring Synthesis from Other Heterocyciic Compounds. 5.1 From Three- and Four-Membered Heterocyciic Compounds. 5.2 From Five-Membered Heterocyciic Compounds... 

Ring Synthesis from Other Heterocyciic Compounds... 

The majority of O-heterocycIic derivatives obtained from phenolic Mannich bases, however, are six-membered rings. In particular, 4-H-chromene (354 in Fig. 138) and... 

Most heterocycies have the same chemistry as their oj>en-chain counterparts. Lactones and acyclic esters beliavc similarly, lactams and acyclic amides behave similarly, and cyclic and acyclic ethers behave similarly. In certain cases, however, particularly when the ring is unsaturated, heterocycies have unique and interesting properties. 

Ring Synthesis from Heterocycies 4.04.3.2.1 Ring opening... 

Pyrazoles can be prepared by ring opening reactions of fused systems already containing the pyrazole nucleus. Thus several [5.5], [5.6] and [5.7] fused heterocycies have been opened to substituted pyrazoles, usually in basic medium. In general, the method has little preparative interest since another pyrazole derivative has usually been used to build the ring-fused system. However, due to the unexpected structures obtained, two publications are worthy of notice. 6//-Cyclopropa[5a,6a]pyrazolo[l,5-a]pyrimidine (638) was readily obtained from the corresponding pyrazolopyrimidine by the action of diazomethane at room temperature (Scheme 59) (81H 15)265). When (638) was treated with potassium hydroxide, the pyrazole (640) was formed, probably via the diazepine (639). 

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. 

Zwanenburg, B., ten Hoite, P. The synthetic potentiai of three-membered ring aza-heterocycies. Top. Curr. Chem. 2001, 216, 93-124. Bonini, B. F., Fochi, M., Comes-Franchini, M., Ricci, A., Thijs, L., Zwanenburg, B. Synthesis of ferrocenyi-oxazoiines by ring expansion of N-ferrocenoyi-aziridine-2-carboxyiic esters. Tetrahedron Asymmetry 2003, 14, 3321-3327. 

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