Condensation generators

The first solid-phase application of the Ugi four-component condensation, generating an 18-member acylamino amide library, was presented in 1999 by Nielsen and Hoel [53]. The authors described a library generation utilizing amino-functionalized PEG-polystyrene (Tentagel S RAM) as the solid support (Scheme 7.36). A set of three aldehydes, three carboxylic acids, and two isonitriles was used for the generation of the 18-member library. 

Substituted allylsilanes such as bromopentadienylsilane 66 of Parrain, Santelli and Roux [35] can be employed in this condensation. Generated with high yields from cheap l,4-bis(trimethylsilyl)-but-2-ene and bromoform, silane 66 reacts under SMS conditions (the use of BF3-OEt2 as the Lewis acid in conjunction with the free alcohol is described in Section 13.4) to yield a new diene 67 (Scheme 13.28). 

The reaction of atomic carbon with A -methylpyrrole 1020 at 77 K generates the A -methyl-3-dehydropyridinium ylide 1021, novel reactive intermediate (Scheme 198), which can be trapped with added hydrogen halides or carbon dioxide <1997JA5091>. The intermediacy of ylide 1021 in the 77 K cocondensation of arc generated carbon with pyrrole 1020 is implied by the fact that addition of methanolic HCl to the cold condensate generates the A -methylpyridinium ion 1023. 

Ge93 M. Ge and K. Sattler, Vapor-Condensation Generation and STM Analysis of Fullerene Tubes, Science 260, 515-518 (1993). 

Vapor-Condensation Generation and STM Analysis of Fuiierene Tubes... 

Scheme 18 illustrates the proposed stages in 6-MSA biosynthesis in which the first and second condensation steps proceed with inversion to give the triketide (63). Ketoreduction gives the alcohol (64) and then elimination followed by a final malonyl condensation generates the tetraketide (65) which cyclises via an intramolecular condensation and enolises to give the aromatic nucleus of (66). In the first set of experiments (J )- and (S)-[l- C, H]nialonales were incubated separately with 6-MSA synthase purified from Penicillium patulum [56]. Isotope incorporations were determined by mass spectrometry. All the possible isotope patterns for retention or loss of the pro-J or pro-S hydrogens from C-3 and C-5 were permutated. Comparison with the actual spectra obtained demonstrated that opposite prochiral hydrogens were eliminated. The absolute stereochemistry was established in an analogous experiment [57] where the chiral malonates were incubated with acetoacetyl CoA rather than acetyl CoA. Subsequent mass spectral analysis showed that it is the Hr proton that is retained at C-3 of 6-MSA and so it can be deduced that the hydrogen at C-5 must be derived from the opposite prochiral hydrogen, Hg. The overall result is summarised in Scheme 18. In a recent collaborative study we have synthesised the triketide alcohol (64) as its NAC thioester and shown that it is indeed a precursor as, on incubation with 6-MSA synthase and malonyl CoA, 6-MSA production is observed [unpublished results]. Current work is aimed at synthesis of both enantiomers of (64) to study the overall stereochemistry of the ketoreduction and elimination reactions.

Figure 12.4 Evaporation-condensation generator for the synthesis of ultrafine metal particles. The cylindrical glass chamber was 0.34 m in diameter and 0.45 m in height. Metal vapor from the alumina crucible mixes with the inert gas. The vapor nucleates particles grow by condensation and deposit on the cooled copper plate by thcrmophorcsis. (After Granqvisi and Buhrman. 1976.)...

Figure 12.5 Sizes of A1 and Cu particles produced in an evaporation-condensation generator. Median particle diameter increased with increasing inert gas pressure and atomic weight. (After Granqvist and Buhrman, 1976.)...

Aerosol Reactors Commercial and Pilot Scale 332 Flame Reactors 332 Pyrolysis Reactors 334 Electron-Beam Dry Scrithhirif 335 Evaporation-Condensation Generators 336 The Collision-Coalescence Mechanism of Primary Particle Formation 338... 

The generally accepted mechanism for the Perkin reaction is shown in Scheme 2. Much of the early woik leading to this view, which was the result of numerous investigations spanning a period of greater than SO years, has been reviewed in some detail. Formation of the anhydride enolate (1) and aldol-type condensation generates the alkoxide anhydride (2). Intramolecular acylation provides an acetoxycaibox-ylate (3), which forms a mixed anhydride elimination of acetic acid and hydrolysis affords the unsatu-... 

Condensation. Generation of stabilized free radicals from dithiocarbonate esters via C—S bond cleavage is promoted by BusSnSnBus. By providing an alkene and a trapping agent, homologation of a carbon chain while performing functionalization, for example,... 

Alcohol- or water-producing condensation generates a three-dimensional network. Pohl and Osterholtz (6) showed that condensation of alkylsilane-triols is specific acid and base catalyzed. Above the isoelectric point of silica (about pH 2.5) condensation proceeds by nucleophilic attack of deprotonated silanols on neutral silicates (6, 23). Below the isoelectric point the reaction proceeds by protonation of silanols followed by electrophilic attack (2, 6). These reactions favor less highly condensed sites, because these are the most electron rich, and lead to more extended, ramified structures. Above pH 2.5, reactions favor more highly condensed sites. 

A power plant burns coal and produces electricity by means of a boiler, turbine, condenser, generator, etc, its steady-state behavior is fairly easy to calculate. However, when the power demand on the generator is suddenly increased or decreased, its behavior is much more difficult to calculate. Power... 

This method is most popular with total condensers generating liquid product. Some of the condenser surface is flooded with liquid at all times. The flow of condensate from the condenser is directly or indirectly manipulated to vary the flooded area. Little heat transfer takes place in the flooded regions, as heat is transferred by sensible heat exchange only (Sec. 15.10). To raise column pressure, the flow of condensate from the condenser is lessened. This increases the flooded area in the condenser and lowers the surface area exposed for vapor condensation. This in turn reduces condensation rate, thereby raising pressure. 

The C21-C37 segment (183) The construction of the polyene chain from aldehyde 185 involved the use of lithiated phosphonate 127 twice as follows Horner-Emmons condensation generated a , , -triene ester which was reduced and oxidized to aldehyde 208 (Scheme 28). Iteration of this process, including a THP cleavage, generated the desired hydroxy aldehyde 183. 

---