Dianion condensation

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

Condensation of the dianion of 1,2-dimercaptobenzene (380) with 1-chloro-8-nitronaphthalene (483) in DMF provided 45% of benzo[2,3]naphthalene [5,6,7-/j][l,4]dithiepin (484) and a small amount of its 5-oxide 485 (Eq. 44) (89JHC667). Though the structure of 485 was adequately determined (NMR studies, X-ray crystallography), its formation was not definitely explained. 

One such compound, bropirimine (112), is described as an agent which has both antineo-plastic and antiviral activity. The first step in the preparation involves formation of the dianion 108 from the half ester of malonic acid by treatment with butyllithium. Acylation of the anion with benzoyl chloride proceeds at the more nucleophilic carbon anion to give 109. This tricarbonyl compound decarboxylates on acidification to give the beta ketoester 110. Condensation with guanidine leads to the pyrimidone 111. Bromination with N-bromosuccinimide gives bropirimine (112) [24]. 

In the reaction of a, a -dilithio salts 285 with benzophenone, di-condensation products were obtained367, whereas in the reaction between the dianion 250 and acrolein only the mono-adduct was obtained328. 

Yields in the acyloin condensation can be improved by running the reaction in the presence of chlorotrimethylsilane MesSiCl, in which case the dianion 36 is converted to the bis silyl enol ether 38, which can be isolated and subsequent )... 

Inspection of Table 2 reveals that all those molecules that suffer a molecular-symmetry reduction in the ground state possess (E2 — E1) values considerably larger than the critical value, so that they should have a fully-symmetrical nuclear configuration in their first excited states. On the other hand, there are cases where a molecule has an ( , — Eg) value significantly higher than the critical value, but has a relatively smaller (Ej— i) value. The ( 2 i) value of the pentalene dianion (I ) is of the same order of magnitude as the critical value and those for the peri-condensed nonalternant hydrocarbon, XVII, the fulvalenes, XXI, XXII and XXIII, and the dianions, IVand VII are significantly smaller than the critical value ( 0.6eV). 

Ligand abbreviations bi = 2,2 -bi-2-imidazoline bt = 2,2 -bi-2-thiazoline bpy = 2,2 -bipyridine phen = 1,10-phenanthroline phy = l,10-phenanthroline-2-carbaldehyde phenylhydrazone bpp = 2,6-bis(pyrazol-3-yl)pyridine paptH = 2-(2-pyridylamino)-4-(2-pyridyl)thiazole 2-pic = 2-picolylamine L = macrocyclic ligand derived from condensation of 2,6-diacetylpyridine with 3,6-dioxaoctane-1,8-diamine Hjthpu = pyruvic acid thiosemicarbazone Hjthpx = pyridoxal thiosemicarbazone salen = dianion of W,iV -ethylenebis(salicylideneimine) H2fsa2en = dianion of fV,JV -ethylenebis(3-carboxysalicylaldimine). 

Similar nucleophilic addition of electrons can also occur to the carbonyl carbon atom of diesters such as (62), e.g. from sodium in solvents such as xylene, but the resultant dianion (63) differs from (59) in possessing excellent leaving groups, e.g. eOEt, and the overall result is the acyloin condensation ... 

Azetidinones.1 The dianion (BuLi) of 1 condenses with the N-aryl aldimine 2 to provide a 1 1 mixture of the trans- and cis-adducts 3. The adducts (3) can be converted by Mitsunobu silylation (inversion), oxidative degradation of the side... 

The synthesis of [Fe4(CO)i3]2- (structure in Fig. 10) has been extensively studied by Hieber and co-workers. The reaction of a variety of ligands1 1 with Fe(CO)s results in redox condensation reactions and formation of the dark red dianion [Fe4(CO)I3]2... 

The redox condensation shown in Eq. (9) gives rise to the dianion [Fe3Ni(CO)12]2 and it has also been possible to isolate salts of the corresponding hydride, [Fe3Ni(CO)12H]- (30.5 r). The presence of infrared absorptions due to bridging carbonyls and the complexity of the infrared spectrum indicate a structure similar to Co4(CO)i2 with the nickel in the basal plane171). 

The catalysed alkylation of l//,4//-pyrazol-5-ones is solvent dependent. In benzene, bis-alkylation occurs at the 4-position whereas, in a carbon disulphide benzene mixture, O-alkylation is observed, although the major product (4, Scheme 5.22) results from nucleophilic attack by the pyrazolone on the carbon disulphide, followed by alkylation of the dithiolate dianion [92]. The catalysed reaction of 2-thiono-3-aryl-thiazolidin-4-ones with alkylating agents under soliddiquid two-phase conditions results in alkylation at the 5-position (60-80%) [93]. The aldol condensation of the thiazolidinones with aryl aldehydes is also catalysed by quaternary ammonium salts. 

Three tactical approaches were surveyed in the evolution of our program. As outlined in Scheme 2.7, initially the aldol reaction (Path A) was performed direcdy between aldehyde 63 and the dianion derived from tricarbonyl 58. In this way, it was indeed possible to generate the Z-lithium enolate of 58 as shown in Scheme 2.7 which underwent successful aldol condensation. However, the resultant C7 P-hydroxyl functionality tended to cyclize to the C3 carbonyl group, thereby affording a rather unmanageable mixture of hydroxy ketone 59a and lactol 59b products. Lac-tol formation could be reversed following treatment of the crude aldol product under the conditions shown (Scheme 2.7) however, under these conditions an inseparable 4 1 mixture of diastereomeric products, 60 (a or b) 61 (a or b) [30], was obtained. This avenue was further impeded when it became apparent that neither the acetate nor TES groups were compatible with the remainder of the synthesis. 

The condensation of dichloride 57 with the dianion of N-methyl ortho-tolylamide 56 affords pyrrolo[2,3-d]-[2]benzazepin-6(lH)-one 58 (R = p-tolyl). The product 58 contains four rather than just two imino groups. This can be explained... 

Osmium (continued) carbide, 24 233 dianion, lA. Xil, 317-319 with phosphines and diphosphines, 30 191 protonation/deprotonation, 30 169 raft hexaosmium clusters, 30 180-182 reactions of condensation, 30 145 with hexafluoroacetone, 30 288 redox, 30 184-185 structural transformations, 30 203 sulfur-containing, synthesis of, 30 147 sulfur derivatives, 24 269, 300-310 synthesis... 

The acyloin condensation is closely related to the radical anion coupling forming pinacolate anions two ester radical anions couple to form a dianion, which readily loses two alkoxide ions. The resulting diketone then is reduced by sodium, first to a semidione radical anion, then to the dianion. Finally, aqueous work-up produces the acyloin. Acyloins are convenient precursors for the generation of semidione radical anions. ... 

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