Good acceptors

Nitro-activated glycals and aromatic compounds are good acceptors for TMM-Pd chemistry. The nitroglycal (19) reacts with (1) to give a 2.4 1 ratio of products (20) and (21) in a combined yield of 69% (Eq. 2). Treatment of the less electron-rich... 

I If one of the carbonyl partners contains no or hydrogens, and thus can t form an enolate ion to become a donor, but does contain an unhindered carbonyl group and so is a good acceptor of nucleophiles, then a mixed aldol reaction is likely to be successful. This is the case, for instance, when either benz-aldehyde or formaldehyde is used as one of the carbonyl partners. 

If S[ is a weak base (low DN) and S2 is a strong base, cations are selectively solvated by S2 conversely, if Sj is a good acceptor (high AN) it will preferentially solvate the anion. As a consequence, the Stokes radii of ions generally change with the composition of a binary solvent. 

A 7r-bonding explanation notes that several ligands high in the trans-effect series are good -acceptors and thus siphon off 7r-density, making the region trans to it electron deficient and thus attractive to ligands that are electron rich. 

Aldehydes up to a chain length of four nonhydrogen atoms are tolerated as acceptors. 2-Hydroxyaldehydes are relatively good acceptors, and the D-isomers are preferred over the t-isomers [180]. Reactions that lead to thermodynamically unfavorable structures may proceed with low stereoselectivity at the reaction center [181]. Recently, a single-point mutant aldolase was found 2.5 times more effective than the wild type in accepting unphosphorylated glyceraldehyde [182,183]. 

Alkylidenemalonate esters are also good acceptors in reactions with silyl ketene acetals of thiol esters under very similar conditions.322... 

Crossed Claisen reactions with two different esters, each of which has a-H atoms, are seldom useful synthetically as there are, of course, four possible products. Crossed Claisen reactions are, however, often useful when one of the two esters has no a-H atoms, e.g. HCOzEt, ArC02Et, (C02Et)2, etc., as this can act only as a carbanion acceptor. Such species are in fact good acceptors, and the side reaction of the self-condensation of the other, e.g. RCH2C02Et, ester is not normally a problem. Intramolecular Claisen reactions, where both C02Et groups are part of the same molecule [e.g. (123)], are referred to as Dieckmann cyclisations. These work best, under simple conditions, for the formation of the anions of 5-, 6- or 7-membered cyclic / -ketoesters... 

Such species should be highly reactive towards acids and bases, since they have high-lying occupied and low-lying unoccupied levels due to strain, which makes them good acceptors and donors of electrons. To test this, EHT calculations were done for the approach of BH3 and NH3 to [4] (22) ... 

With good acceptors, apparent Fmax values increase with increasing acceptor concentration by a factor of about three at 600 mM maltose concentration.36 They decrease, as do initial reaction rates, with increasing concentrations of such weak... 

Because of their low intrinsic electronegativities, neutral late transition metals (bearing an abundance of lone pairs) can serve as good donors in nM— ctah interactions of the form (5.69a). Furthermore, transition-metal-hydride bonds (Section 4.4.1) often display sufficient covalency or polar-covalency (particularly in transition-metal cations) to serve as good acceptors in ns— ctmh interactions of the form (5.69b). In the present section we shall briefly examine the simple example of platinum dihydride (PtH2) as a water-mimic in binary H-bonded complexes with H20,... 

Apart from pharmacophore-based approaches, a variety of methods were applied to decipher important ligand features of PXR activation. VolSurf descriptor-based partial least squares (PLS) regression-based models pointed toward amide responsive regions that implicated good acceptor abilities as key variables [33]. 

Typical experimental data are shown in Table 52. As can be seen, the diaxial conformation is preferred for the cases in which adjacent substituent bonds are hermaphroditic, i.e. simultaneously very good donor and very good acceptor bonds. 

The requirements for Case 2, a low it barrier and a high steric barrier, could be expected to be fulfilled by some of the 2,2-bis(dimethylamino)ethylenes discussed in Sect. II-B-4, but NMR spectra show that they belong to Case 1, probably because E, (0°) is diminished by the out-of-plane twist of the dimeth-ylamino groups. However, when this twist is prevented by cyclization, and when X and Y are good acceptors, representatives for Case 2 result. 

Ligand (342) is a good acceptor, and reacts with [RuCl2(dmso)4] to give [RuCl2(342)2] and [RuCl2(dmso)2(342)], the crystal structure of which has been determined. ... 

Compounds that are more polar, and which can better hydrogen-bond with water, require less drastic alterations to the solvent environment to cause dissolution to occur. On the right side of Figure 3, we associate solute polarity with each formulation concept. Drugs that are good hydrogen donors, in the extreme sense, have acidic properties. Likewise, those that are very good acceptors have basic properties. For these compounds, formation of a salt by protonation or deprotonation is a feasible route. 

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