Dilute condition

Synthesis by high-dilution techniques requires slow admixture of reagents ( 8-24 hrs) or very large volumes of solvents 100 1/mmol). Fast reactions can also be carried out in suitable flow cells (J.L. Dye, 1973). High dilution conditions have been used in the dilactam formation from l,8-diamino-3,6-dioxaoctane and 3,6-dioxaoctanedioyl dichloride in benzene. The amide groups were reduced with lithium aluminum hydride, and a second cyclization with the same dichloride was then carried out. The new bicyclic compound was reduced with diborane. This ligand envelops metal ions completely and is therefore called a cryptand (B. Dietrich, 1969). 

The intramolecular version for synthesizing cyclic and polycyclic compounds offers a powerful synthetic method for naturally occurring macrocyclic and polycyclic compounds, and novel total syntheses of many naturally occurring complex molecules have been achieved by synthetic designs based on this methodology. Cyclization by the coupling of an enone and alkenyl iodide has been applied to the synthesis of a model compound of l6-membered car-bomycin B 162 in 55% yield. A stoichiometric amount of the catalyst was used because the reaction was carried out under high dilution conditions[132]. 

The logic that leads us to this last result also limits the applicability of the ensuing derivation. Applying the fraction of total lattice sites vacant to the immediate vicinity of the first segment makes the model descriptive of a relatively concentrated solution. This is somewhat novel in itself, since theories of solutions more commonly assume dilute conditions. More to the point, the model is unrealistic for dilute solutions where the site occupancy within the domain of a dissolved polymer coil is greater than that for the solution as a whole. We shall return to a model more appropriate for dilute solutions below. For now we continue with the case of the more concentrated solution, realizing... 

Cyclic aryl ether ketones have been prepared from l,2-bis(4- uoroben2oyl)ben2ene and bisphenols under pseudo high dilution conditions. These materials undergo ring-opening polymeri2ation in the presence of an anionic catalyst (87). 

FIG. 12-29 Solids in a dilute condition near the top of a spray dryer. 

Through circulation. The gas penetrates and flows through interstices among the solids, circulating more or less freely around the individual particles (Fig. 12-32). This may occur when solids are in static, moving, fluidized, or dilute conditions. 

A gas-sohds contacting operation in which the sohds phase exists in a dilute condition is termed a dispersion system. It is often called a pneumatic system because, in most cases, the quantity and velocity of the gas are sufficient to lift and convey the sohds against the force of gravity. Pneumatic systems may be distinguished by two characteristics ... 

Tire first C—O bond formation is probably not influenced strongly by the presence of a templating cation. Since it is not crucial for one end of the chain to meet the other rather than reacting with a different molecule, it is not necessary to superimpose either a template or dilution condition on the reaction to prejudice the statistics. In the second step, however, such a prejudicial condition is required. This is available in the form of an... 

The one-pot synthesis of 9 described above appears to afford only modest yields of azacrowns. One might wonder why any crown at all would be formed under non-high dilution conditions intended to yield only open-chained material. Vogtle suggests that this can be explained in terms of template, steric and entropy effects . These factors are of doubtless significance, but it is interesting to note that in the synthesis of poly-azamacrocycles, Richman and Atkins found that there was no significant template effect observed. The question of the template effect in Ihe syntheses of 9 has recently been addressed by Kulstad and Malmsten They conclude that the formation of 9 is assisted by the presence of alkali metal cations. 

Shortly after their first report of all-oxygen bridged cryptands, Dietrich, Lehn and Sauvage reported incorporation of sulfur in the strands. The experimental methods used were essentially similar to those applied in the syntheses of the parent cryptands. As in previous cases, a diacyl chloride was condensed with a diamine under high dilution conditions. In this case, however, the diamine contained sulfur atoms rather than oxygen. The synthesis of compound 5 was accomplished in two stages as illustrated below in Eq. (8.3). The first cyclization step affords the macrocyclic amine in 55% yield. The macrobicyclic product (5) is formed in 25% yield from the monocyclic diamine and the acid chloride. 

In the latter process Dieckmann cyclization of diester (11) using high dilution conditions failed. However, A-homo-5a-cholestan-3-one (5b) identical to the product of diazomethane ring enlargement of (lb) was obtained in 35 % yield when diester (11) was hydrolyzed to the bis-homo diacid and this converted to the thorium salt and pyrolyzed. 

BF3 Et20, EtSH, CH2CI2, rt. 76-96% yield. It is possible to achieve some selectivity for a secondary derivative over a primary one when the reaction is conducted under more dilute conditions. 

Lisk and Stacy reported " a dependence of concentration on the formation of the isomers. Under concentrated conditions (2 parts Dowtherm A to 1 part enamino-ester) the 5-isomer was almost formed exclusively, while under dilute conditions (30 1), the 7-isomer predominated. 

The Friedel-Crafts cyclization of w-(2-thienyl) substituted longer fatty acids (130, n = 5,8,9) under high dilution conditions has been investigated by Goldfarb et They used boiling ethereal AlClg,... 

The well-known phenomenon of smell-fatigue is explained by the theory that actual chemical reaction takes place between the odoriferous body and some reacting material in the nose thus it can easily be conceived that some sort of addition reaction takes place and that directly the osmoceptor in the nose becomes saturated no further reaction is possible and no further odour can be appreciated until fresh osmoceptor has been formed. Ruzicka has suggested that two such osmoceptors are involved since substances inspired in a concentrated state have odours different to those perceived in a dilute condition. He suggests that one osmoceptor reacts more readily than the other and in consequence is the more readily saturated or consumed, this osmoceptor is responsible for the sensation produced when dilute odours are inspired. If the odour be concentrated, the first osmoceptor is saturated almost instantaneously and then the sensation produced is the result of the reaction between the odoriferous substance and the second osmoceptor. 

Linear case This case is met when the adsorption isotherm is considered linear, which means operation under diluted conditions. Taking into account the saturation capacities of the CSP, this behavior is usually met for concentrations around or below 1 g for separation of enantiomers. 

Additions of carbon nucleophiles to vinylepoxides are well documented and can be accomplished by several different techniques. Palladium-catalyzed allylic alkylation of these substrates with soft carbon nucleophiles (pKa 10-20) proceeds under neutral conditions and with excellent regioselectivities [103, 104]. The sul-fone 51, for example, was cyclized through the use of catalytic amounts of Pd(PPh3)4 and bis(diphenylphosphino)ethane (dppe) under high-dilution conditions to give macrocycle 52, an intermediate in a total synthesis of the antitumor agent roseophilin, in excellent yield (Scheme 9.26) [115, 116]. 

The conjugate addition to acyclic enones is summarized in Table 5. The chiral hetero-cuprate derived from (S)-prolinol or cinchonidine produced products of low enantiomeric excess on treatment with chalcone (entries 3 and 4), while the cuprate from (S)-yV-methylpro-linol gave 64% ee (entry 6). Under more dilute conditions, 88% cc was obtained (entry 5). (2[Pg.909]

However, the former reaction requires very low temperatures and very dilute conditions and the latter uses an unstable and explosive brominating reagent. 

When disodium (Z)-l,2-dicyanoethene-l,2-dithiolate and 1,3-dibromopropane are cyclized under high dilution conditions, the desired 14-membered macrocyclic tetrathioether was isolated <96LA1005>. 

Condensation of dicesium 2-thioxo-l,3-dithiole-4,5-diselenolate with fo/s-alkylating polythioethers under high dilution conditions afforded the TTF-containing macrocycles possessing soft donor sites and 12-, 15-, and 18-membered rings <%JCS(P1)1995>. 

Monoalkylation of Af-tosylallylamine 10 with dibromoalkane 101 proceeded in 60-90% yield (Eq. 10 see also Scheme 3 and Eq. 2) [17]. The bromoalkyl-amines 102 were converted to nitro compounds 103. In situ transformation of 103 into nitrile oxides led to spontaneous cycloaddition with formation of isox-azolines fused to 5-, 6-, and 7-membered ring heterocycles 104 a-c. Under very high dilution conditions, 103 d was converted to 104 d, an isoxazoline fused to an 8-membered azocine, in low (10%) yield. 

The conversion of the dehydrotrimer 135 into the corresponding bis-cuprate followed by coupling with dibromide 131 (Cadiot-Chodkiewicz conditions) gave the expanded [5]pericycline 122 in 53% isolated yield (Scheme 28) [4]. The more versatile approach by simple oxidative cyclooligomerization of dehydrooligomers of type 135 under high dilution conditions as shown in Scheme 28 provided the acetylene-expanded [3]- 82, [5]- 122 and [6]pericyclines 163 in reasonable to excellent yields [4,7]. 

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