Cyclic condensation

Id. Cyclic Condensation Polymers.—The foregoing discussion has proceeded under the assumption that the only products of bifunctional condensation are open chain polymer molecules—an assumption which obviously will not be exactly valid since cyclic polymers must always occur to some extent. The nature of the error introduced by this assumption will be examined in the course of the following discussion of cyclic polymer components. 

Conjugated Schiff base macrocycles containing a 1,3,4-oxadiazole moiety were prepared by [1+1] cyclic condensation <2002SC3339>. 

In view of the reports of the instability of solutions in which the formation of tert-butyl cations had been attempted and of the formation of allylic ions from cyclic condensation... 

Calix[n]arenes (n=4,6,8) are cyclic condensation products of ap-substituted phenol and formaldehyde [58]. Gutsche and co-workers [59,60] have developed procedures for the synthesis of calixarenes and caHxarene derivatives. 

Alkaline Degradation. At high pH, sucrose is relatively stable however, prolonged exposure to strong alkali and heat converts sucrose to a mixture of organic acids (mainly lactate), ketones, and cyclic condensation products. The mechanism of alkaline degradation is uncertain however, initial formation of glucose and fmctose apparendy does not occur (31). In aqueous solutions, sucrose is most stable at —pH 9.0. 

Glycols may undergo intramolecular cydization or cyclically condense with other molecules to form a number of ring structures. Transesterification of carbonates with ethylene glycol produces ethylene carbonate [96 49-1] (eq. 4). Numerous materials catalyze carbonate transesterifications. 

In this review, the term acetal will be used to connote a cyclic compound (I) formed, together with one mole of water, by the condensation of an aldehyde with an equimolecular proportion of a glycol, and not, as is more usual, an acyclic compound derived from one mole of an aldehyde and two moles of a monohydric alcohol. A compound which contains more than one such ring system will be termed a diacetal, triacetal, etc. In an analogous fashion, cyclic condensation products (II) obtained from ketones will be called ketals. ... 

R. Niemeyer (1976). Cyclic condensed metaphosphates and linear polyphosphates in brown and red... 

Cyclic condensation of o -methylselenoacetophenone oxime with PPA affords 2-methyl-benzoselenazole (28a) (78JHC865). 

Selenazolidine-2-carboxylic acid (95) is prepared by reduction of selenocysteamine and subsequent treatment with sodium glyoxylate (Scheme 38) (79MI42000). ( )-Selenazolidine-4-carboxylic acid (96) is synthesized in good yield by cyclic condensation of DL-selenocysteine with formaldehyde (Scheme 39) (77MI42000). 

Selenadiazoline (172) and similarly very crowded derivatives are prepared as outlined in Scheme 78 (76JCS(P1)2079). Cyclic condensation of selenosemicarbazide and carboxylic acids affords the 2-acylamino derivative (184) and, by hydrolysis, 2-amino-l,3,4-selenadiazoles (185 Scheme 79) (71JHC835, 73JPS839). 

Diamine oxidase catalyzes the oxidation of various diamines (e.g., putrescine, cadaverine) to their corresponding aminoaldehydes, which are in equilibrium with their cyclic condensation products (A -pyrroline and A -piperideine, respectively). Diamine oxidase activity has been proposed to be a marker of intestinal mucosa integrity. 

Zeiss and co-workers further found that acetylenes displace THF molecules in the coordination sphere of chromium and other metals in analogous complexes. The acetylenes subsequently condense in cyclic arrangements, and such cyclic condensation reactions have provided important new routes to both arene-metal complexes and uncomplexed arenes. Further details on these novel reactions are contained in the reviews at the end of this section. 

The diamagnetic cation [(Me8Cg)2Mn] has been reported from the cyclic condensation of 2-butyne on diphenylmanganese 416). However, an attempt to reproduce this result led instead to the mixed arene cation... 

Calix[n]arenes are cyclic condensation products of para-substituted phenol derivatives and formaldehyde [29], They are highly interesting for the development of sensitive coatings due to their conformational flexibility and the ease by which they may be modified chemically. Chemical modification can be done either in the meta position, or by reactions at the hydroxy group. In this way, bulky substituents [30], chelating substituents [31], aromatic residues [32], crown ethers [33,34], peptides [35,36], etc. can be introduced. A first approach to combinatorial synthesis of calix[4]arene receptors has been published by Reinhoudt and co-workers [37,38], who prepared calixarenes with different substituents. In solution, these calixarenes lead to formation of hetero-oligomers with barbiturates, and these hetero-oligomers were detected by MALDI-TOF mass spectrometry and H-NMR spectroscopy. 

The method most widely used today to recover pbthalic anhydride from the reactor effluent consists in passing this stream through cyclic condensation systems. In some of them, operating as crystallizers, the anhydride solidifies by cooling in finned tubes, whereas in the others, hot oil is introduced to melt their content and to recover the previously-deposited product In this way, up to 99 per cent of the phthalic anhydride in the effluent can be recovered. 

In other experiments, the ditosylate ester reactant was found to decompose during the slow cyclic condensation reaction using carbonate bases. This de-... 

The [18]N2P4 macrocycle was prepared by a 2 2 cyclic condensation of bis(2-chloroethyl)propylamine and the dipotassium salt of l,2-bis(phen-ylphosphino)ethane in THF (method AA-4) (Ciampolini et al., 1983). 

Curtis and others showed that cyclic condensation also was possible in the absence of a metal template ion, but acid was necessary for those reactions. Possibly, the protonated amines formed an internal hydrogen-bonding network that acted as a template. Cyclization was observed in yields of up to 80% (Curtis and Hay, 1966 Kolinski and Korybut-Daszkiewicz, 1969 Tait and Busch, 1978a, 1978b). The isomers of the formed cyclic Schiff bases were difficult to separate. Reduction of the unsaturated macrocycles gave cyclic polyamines with up to six chiral centers and up to 20 diastereomeric isomers (Hay and Piplani, 1977 Kolinski and Korybut-Daszkiewicz, 1969). 

Formation of 89 has been favoured on the account of 90 with the increasing steric hindrance of the phenolic moiety. 89 was the main product with 2,6-di-ferf-butylphenol. It effectively protects squalene against autoxidation [3,4]. The cyclic condensate 90 thermolyses and releases PD. The reactivity of BQDI with 2,6-dialkylphenols slows down the consumption of PD, but cannot prevent it. 

But-2-yne undergoes cyclic condensation when reacted with triphenylchro-mium(III) tetrahydrofuranate to yield hexamethylbenzene and bis-hexamethyl-benzene-chromium complex in the same reaction 1,2,3,4-tetramethylnaphthalene... 

An early demonstration of the template effect in the synthesis of macrocyclic ligands was the metal-ion-controlled cyclic condensation of 2,6-diacetylpyridine with 3,3 -diaminodipropylamine to give complexes of the 14-membered N4 ring (118), usually abbreviated (Me2pyo[14]triene i ). Effective template ions include Ni", Co" and Cu". Well-characterized iron complexes have not been... 

Initially a great majority of tetradentate cyclic polyamines were prepared by condensation reactions assisted by a transition metal ion, typically nickel(II), which held the reacting molecules in favourable positions to facilitate their cyclic condensation (template reactions).The archetypal template reaction was due to the pioneering work of N. F. Curtis, who found that [Ni(en)3](C104)2 reacts with acetone at room temperature yielding... 

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