Condensation cyclo

The student is recommended to carry out the Diels and Alder diene synthesis when making preparations from the original literature. For example, he should condense cyclo-hexadiene with quinone (Annalen. 1933, 507, 288) or furane with maleic anhydride (Ber., 1929, 62, 554). 

Iminium catalysis directly utilizes the higher reactivity of the iminium ion in comparison to the carbonyl species and facilitates Knoevenagel-type condensations, cyclo- and nucleophilic additions, and cleavage of cr-bonds adjacent to the a-carbon. Enamine catalysis on the other hand involves catalytically generated enamine intermediates that are formed via deprotonation of an iminium ion, and react with various electrophiles or undergo pericyclic reactions. ... 

Cycloaddition reaction of two molecules of alkyne and alkene is a direct route for the synthesis of substituted cyclohexadiene derivatives, which are important components of the Diels-Alder reaction. Therefore, the reaction cycloisomerization of enediyne azamacrocycles represents a pathway to the synthesis of highly functionalized tetra-condensed cyclo-hexadienes in a single step. The synthetic variety of such reactions is... 

The three monomethylthiazoles and 2,5-dimethylthiazole undergo the same type of cyclo addition with rearrangement when condensed with DMA in DMF (Scheme 54) (335, 339). 

Acheson et al. (336) by the condensation of DMA with 2,4-dimethyl-thiazole in THF (Scheme 56). As Reid et al. (335) first proposed, the adduct of 2,4-dimethylthiazole with DMA in DMF (93) results from the normal cyclo-addition with rearrangement (Scheme 57). The conclusive demonstration of this structure was recently given by Acheson et al. (339)... 

Properties of ferrocene-containing polymers have been improved by inclusion of pyrazole systems in the backbone. The synthesis of (748) was achieved by condensation of bis()3-diketoferrocenes) with aromatic dihydrazines to give polyhydrazones that were later cyclo-dehydrated (B-80MI40408). 

Tropolone has been made from 1,2-cycloheptanedione by bromination and reduction, and by reaction with A -bromosuccinimide from cyolo-heptanone by bromination, hydrolysis, and reduction from diethyl pimelate by acyloin condensation and bromination from cyclo-heptatriene by permanganate oxidation from 3,5-dihydroxybenzoic acid by a multistep synthesis from 2,3-dimethoxybenzoic acid by a multistep synthesis from tropone by chlorination and hydrolysis, by amination with hydrazine and hydrolysis, or by photooxidation followed by reduction with thiourea from cyclopentadiene and tetra-fluoroethylene and from cyclopentadiene and dichloroketene. - ... 

In preparing cyclohexene by the dehydration of cyclo-hexanol with sulfuric acid (Org. Syn. Coll. Vol. i, 177) the time can be shortened to about two hours by boiling the mixture in a round-bottomed flask provided with a reflux condenser with water maintained at about 75°. A tube at the top leads to a downward cold-water condenser. 

With one exception no other high molecular weight linear polyesters have achieved any sort of commercial significance for films and fibres. The one exception is the condensation polymer of dimethyl terephthalate and 1,4-cyclo-hexylene glycol (also known as 1,4-cyclohexanedimethanol) (Figure 25.19). 

The original compound, maleimide (2,5-dioxo-A -pyrroline), is synthesized by the cyclo-condensation of ammonia and maleic acid. Similarly, primary amine is added to maleic anhydride, followed by cyclocondensation, to form N-substituted maleimide (Fig. 2). This reaction is applied to the preparation of bis-maleimides (BMl) [1]. At first, BMI was used as a crosslinking agent for natural rubber (NR). An o-dichlorobenzene solution of NR was crosslinked by BMI at I08-150°C in the presence of peroxides. The radicals generated from peroxides react with the double bonds of both BMI and NR [ 1 ]. 

Frensch and Vdgtle have recently appended three crown ether units to the cyclo-triveratrylene unit . Note that Hyatt had previously prepared the open-chained relatives of this structure (see Sect. 7.3 and Eq. 7.6). Whereas Hyatt prepared the cyclo-triveratrylene skeleton and then appended polyethyleneoxy arms to it, Frensch and Vogtle conducted the condensation reaction (formaldehyde/HCl) on the preformed benzocrown. Thus benzo-15-crown-5 was converted into the corresponding tris-crown (IS) (mp 203.5—205.5°) in 4% yield. The yield was somewhat higher for the condensation of benzo-18-crown-6, but in both cases, yield ranges were observed. These species formed 1 3 (ligand/salt) complexes with sodium and potassium ions. 

Application of this scheme to condensation products of cyclo-alkanones affords the cycloalkenyl-substituted barbiturates. 

Wallach has synthesised i-menthone by condensing 1, 4-methyl-cyclo-hexanone with bromo-isobutyric ester from the condensation product he prepared i-menthene, which was converted into i-menthenone, by means of its nitrosochloride, whence i-menthone resulted by reduction. 

The synthesis of pyrido[2,3-d]pyrimidin-7(8H)-ones has also been achieved by a microwave-assisted MCR [87-89] that is based on the Victory reaction of 6-oxotetrahydropyridine-3-carbonitrile 57, obtained by reaction of an Q ,/3-unsaturated ester 56 and malonitrile 47 (Z = CN). The one-pot cyclo condensation of 56, amidines 58 and methylene active nitriles 47, either malonitrile or ethyl cyanoacetate, at 100 °C for benzamidine or 140 °C for reactions with guanidine, in methanol in the presence of a catalytic amount of sodium methoxide gave 4-oxo-60 or 4-aminopyridopyrimidines 59, respectively, in only 10 min in a single-mode microwave reactor [87,88]... 

Scheme 36 Cyclo-condensed prolines via intramolecular cycloaddition...

PtRu nanoparticles can be prepared by w/o reverse micro-emulsions of water/Triton X-lOO/propanol-2/cyclo-hexane [105]. The bimetallic nanoparticles were characterized by XPS and other techniques. The XPS analysis revealed the presence of Pt and Ru metal as well as some oxide of ruthenium. Hills et al. [169] studied preparation of Pt/Ru bimetallic nanoparticles via a seeded reductive condensation of one metal precursor onto pre-supported nanoparticles of a second metal. XPS and other analytical data indicated that the preparation method provided fully alloyed bimetallic nanoparticles instead of core/shell structure. AgAu and AuCu bimetallic nanoparticles of various compositions with diameters ca. 3 nm, prepared in chloroform, exhibited characteristic XPS spectra of alloy structures [84]. 

A tandem enzymatic aldol-intramolecular Homer-Wadsworth-Emmons reaction has been used in the synthesis of a cyclitol.310 The key steps are illustrated in Scheme 8.33. The phosphonate aldehyde was condensed with dihydroxyacetone phosphate (DHAP) in water with FDP aldolase to give the aldol adduct, which cyclizes with an intramolecular Horner-Wadsworth-Emmons reaction to give the cyclo-pentene product. The one-pot reaction takes place in aqueous solution at slightly acidic (pH 6.1-6.8) conditions. The aqueous Wittig-type reaction has also been investigated in DNA-templated synthesis.311... 

In the manufacture of aniline by the hydrogenation of nitrobenzene, the off-gases from the reactor are cooled and the products and unreacted nitrobenzene condensed in a shell and tube exchanger. A typical composition of the condensate is, kmol/h aniline 950, cyclo-hexylamine 10, water 1920, nitrobenzene 40. The gases enter the condenser at 230 °C and leave at 50 °C. The cooling water enters the tubes at 20 °C and leaves at 50 °C. Suggest suitable materials of construction for the shell and the tubes. 

In the production of aniline by the hydrogenation of nitrobenzene, the reactor products are separated from unreacted hydrogen in a condenser. The condensate, which is mainly water and aniline, together with a small amount of unreacted nitrobenzene and cyclo-hexylamine, is fed to a decanter to separate the water and aniline. The separation will not be complete, as aniline is slightly soluble in water, and water in aniline. A typical material balance for the decanter is given below ... 

The condensation reactions described above are unique in yet another sense. The conversion of an amine, a basic residue, to a neutral imide occurs with the simultaneous creation of a carboxylic acid nearby. In one synthetic event, an amine acts as the template and is converted into a structure that is the complement of an amine in size, shape and functionality. In this manner the triacid 15 shows high selectivity toward the parent triamine in binding experiments. Complementarity in binding is self-evident. Cyclodextrins for example, provide a hydrophobic inner surface complementary to structures such as benzenes, adamantanes and ferrocenes having appropriate shapes and sizes 12) (cf. 1). Complementary functionality has been harder to arrange in macrocycles the lone pairs of the oxygens of crown ethers and the 7t-surfaces of the cyclo-phanes are relatively inert13). Catalytically useful functionality such as carboxylic acids and their derivatives are available for the first time within these new molecular clefts. 

Piccinni-Leopardi, C. et al., J. Chem. Soc., Perkin Trans. 2, 1986, 91 Cyclo-condensation of the 2 components gives 2,6-dimethyl-l,3-dioxa-2,6-diphos-phacyclooctane, and its subsequent distillation (65-68°C/0.07 mbar) must be effected with bath temperatures below 120°C to avoid explosion. 

Alkylidenetetrahydrofurans underwent a cyclo-condensation with amidines to give 4-(3-hydroxyalkyl)pyrimidines, as can be seen below <06T5426>. 

Feist-Benary cyclo-condensation of (2,4-dioxobutylidene)-phosphoranes with a-chloroacetone gave rise to substituted furfuryl phosphonium salts, which underwent subsequent Wittig reactions to afford alkenylfurans in good yields as can be seen below <06JOC8045>. 

Scheme 4. Condensed free-energy profile (kcalmol-1) of the complete catalytic cycle of the C8-reaction channel of the nickel-catalyzed cyclo-oligomerization of 1,3-butadiene for catalyst IV with L = P(OPh)3. The favorable [Ni°(p2-tr

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