Ring five-membered, carbocyclic

The effectiveness of various sources of fluoride ion in the displacement of the trifluoromethanesulfonic group has been demonstrated while introducing a fluorine atom into the five-membered carbocyclic ring of a prostaglandin precursor Treat tnent of the corresponding triflyl derivative with potassium fluoride in acetonitrile or with cesium fluonde in refluxing diinethylformamide or hexamethylphosphoric... 

The following syntheses of five-membered carbocyclic systems involve radical-induced epoxide fragmentation with radical translocation and cyclization. The resulting bicyclic alcohols are formed as a mixture of two epimeric esters with cw-fused rings.[71]... 

The Pauson-Khand reaction (PKR) [96] consists of the synthesis of cyclopen-tenones by reaction of an alkene with a dicobalthexacarbonyl complexed alkyne (Scheme 57) and has recently emerged as one of the methods of choice for the obtainment of five-membered carbocyclic rings [97]. Its unique atom connectivity, which involves the two unsaturated carbons of the reagents and the carbon atom of a carbon monoxide ligand of cobalt usually in a regioselective manner (Scheme 57), has brought to refer to PKR as a [2 -I- 2 + 1] cycloaddition. 

Five-membered carbocycles are the most easily formed [45, 107, 196, 200, 202,203]. Five-membered carbocyclic rings can be formed (with 2% MoF6 as the catalyst) even when the double bond is tetrasubstituted (Eq. 24) [200]. The stability of the catalyst toward the free OH group in this case is noteworthy. Evidently this particular t-butoxide-like alcohol does not react with this particular catalyst for steric reasons. Six-membered carbocyclic rings are also formed readily (Eq. 25) [200], as are seven-membered rings, especially if one takes advantage of a Thorpe-Ingold effect (e.g., Eq. 26) [20] or a similar conformational predisposition for the double bonds to remain near one another. 

The syntheses of l,2,3,5,6,8a-hexahydroindolizine (1) and (-)-swainsonine were successfully carried out via a ROM-RCM strategy, and final CM with ethylene to free the ruthenium. Two different synthetic routes were implemented to achieve a similar compound. In the case of l,2,3,5,6,8a-hexahydroindolizine 1, the six-membered ring was established first using RRM and in the case of (-)-swainsonine, the five-membered ring was established first. In both cases, the ring rearrangement precursors were enantiomerically pure five-membered carbocycles, which can be synthesised efficiently from racemic starting materials. 

Dicarbonate 14 was used as the starting material to achieve both cis-and trans- ring rearrangement precursors 15 and 16. ROM-RCM of the five-membered carbocycles 15 and 16 leads to 17 and 18. These compounds contain a terminal double bond at position 9, which can be easily functionalised and are set up to form the tricyclic tetraponerines. 

This section follows the content of Section 9.02.8 in CHEC-II(1996) without repetition of data presented in the latter but refers to several papers omitted in CHEC-II(1996) along with new publications. Below are presented various synthetic methods, which are classified by the nature and size of the starting ring. Peculiar differences with CHEC-11(1996) should be marked (1) the absence of paragraphs devoted to formation of oxepine derivatives from four- and five-membered carbocycles because new syntheses of these kinds were not found in the literature (2) Sections 13.02.8.2.2, 13.02.8.2.5, and 13.02.8.2.6, which are new, appear concerning with formation of oxepine derivatives from four-, (other) seven-, and eight-membered heterocycles, respectively. 

Synthesis of Five-Membered Carbocyclic and Heterocyclic Ring Systems... 

With the radical controversy solved, Bailey and others set about the detailed investigation of anionic cyclisation as a synthetic method for the formation of five-membered carbocyclic rings, and we shall divide the remainder of this section, which covers work published between 1987 and 2000, into the main classes of compounds produced by the cyclisation cyclopentanes, furans, pyrrolidines, and polycyclic products. It turns out that organolithiums are unique among the alkali metals in their ability to undergo anionic cyclisation to give cyclopentanes, particularly where primary organometallics are concerned.121... 

The formation of ring systems by the anionic cyclization of olefinic alkyl, aryl and vinyl-lithiums is an interesting synthetic transformation that provides a regiospecific and highly stereoselective route to five-membered carbocycles and heterocycles99. Most importantly, it is possible to functionalize the initially formed cyclization product by a tandem reaction with electrophiles, a reaction that is not generally possible in the case of radical cyclizations. 

The next four procedures describe the regioselective preparation of bicyclic ring systems, specifically, condensed five-membered carbocyclic derivatives. A large... 

Although there are only a few examples of alkylations of carboxylate enolates which are exocyclic to five-membered carbocyclic rings, the usual steric factors seem to control the stereoselectivity of these reactions. Thus, the dienolate (111) underwent reaction with 4-bromo-l-butene anti to the methoxymethyl substituents with high diastereoselectivity " and enolates derived from norbomane-2-carboxylates (112)... 

Draw one canonical form for each of the following aromatic compounds a three-membered carbocyclic cation with 2 electrons (n=0, 3 p sub-orbitals) a five-membered carbocyclic anion with 6 electrons (n= 1, 5 p sub-orbitals) and a six-membered neutral ring containing one nitrogen atom and five carbon atoms (n= 1, 6 p sub-orbitals). 

J SYNTHESIS OF FOUR- AND FIVE-MEMBERED CARBOCYCLIC RINGS... 

Oxazine JV-oxides 386 obtained from cross-conjugated keto enamines 384, and 1-nitrocyclohexene 385 do not ring open to nitroalkylated enamines, but undergo ring fission and rearrangement to five-membered carbocycles - . Nucleophilic ring fission of 386 to the intermediate 387 followed by recyclization gave the hexahydroindene... 

An interesting approach to the substituted 6,8-bisdehydro[13]annulenone (238) includes a double Knoevenagel reaction of the mixed acetonedicarboxylic ester (235) with aldehyde (236) in the presence of piperidine to give (237). Oxidative coupling of the acetylene moieties in (237) with Cu(OAc)2 in pyridine affords (238) in 10% yield (Scheme 47).2 a,p-Unsaturated malonodinitriles are suitable intermediates for the synthesis of a variety of carbocyclic systems. Cyclization of the benzylidene malonodinitrile (239) to form a five-membered carbocyclic ring (240) can be achieved upon treatment with acid and subsequent hydrolysis (Scheme 48). A similar cyclization of (241) affords six-mem-bered carbocyclic ring systems. ... 

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