Donor alkyl

However, strong protic acid catalysts are needed when 7T- or CJ-donor alkylating agents are used to produce carbocationic or highly polarized donor-acceptor-complexes as the reactive alkylating iatermediates ... 

Incorporating an electron-donor alkyl group into position 2 of 2 was shown by foe present authors to facilitate S-oxidation thus, 2-efoyl-thieno[3,2-6]thiophene-l,1-dioxide (214) was prepared at40°-45° from 2-ethylthieno[3,2-6]thiophene, hydrogen peroxide and acetic acid. The thieno[3,2-6]thiophene system undergoes oxidation even if foe second a-position is carboxy-substituted oxidation of 5-efoylthieno[3,2-6]-thiophene-2-carboxylic acid furnished foe 4,4-dioxide (215) subsequently decarboxylated to sulfone (214) [Eq. (70)]. The [2,3-6] isomers, 20 and 55, with foe sulfur atoms bound to foe same carbon atom, do not form sulfones under similar conditions. 

Cyclohexane dimethanol divinyl ether (donor)-alkyl maleimide (acceptor)... 

C. Complexes with a-donor (alkyl, aryl) ligands 114... 

The cyclobutene ring is substituted by a donor alkyl chain, which tends to rotate outwards, and by an attractor carbonyl which tends to rotate inwards the product is... 

The example shows a sequential approach to the study of discrete variations. The Willgerodt-Kindler reaction was studied with a set of para substituted acetophenones, see Schema 9. As the reaction failed with strong electron-withdrawing substituents, the study was limited to include donor, alkyl, and halogen substituents. 

The two competing transition states for the cycloaddition between 4-nitrobenzonitrile oxide and 4,4-dimethyl-3-hydroxypentene have been calculated by a combination of ab initio and MM2 calculations35. Since the same sense of selectivity and the same type of interactions are expected in the osmylation reaction, extrapolation of these results to the latter transformation has been proposed (model C). The major product is believed to arise from the staggered36, 37 transition state which has the best ff-donor (alkyl, silyl or stannyl) anti to maximize electron donation from its high lying orbital to the LUMO of the transition state. Since this structure implies a [3 + 2]-type cycloaddition, the inside position, less crowded than the outside position, is best occupied by the oxygen atom. 

The dipolarophilicity of nitriles can be enhanced by coordination to a metal center, namely toward azides or nitrones, [-0+N(R3)=C(R1)(R2)], to yield, via [2 + 3] cycloadditions, the tetrazolate complexes (1) and (2) (Table 5, the latter derived from the former by sterically promoted linkage isomerization) with a wide variety of metal centers4 and the A4-l,2,4-oxadiazoline complexes (3) with Pt centers,175 respectively. The reactions normally proceed under mild conditions, even for nitriles with electron-donor alkyl groups (R). The tetrazoles177 and the oxadiazolines175 were liberated in some cases and the metal-mediated processes constitute promising routes for the synthesis of such heterocycles as exhibit medicinal and other applications. 

Electron-releasing groups are best anionic, next the less electronegative pi-donors, alkyl substitution, and least, very electronegative pi-donors with poor 2p-2>p overlap. 

Others Telomerization, macromers by chain transfer, bimetallic chain transfer, electron donors, alkyl iodide mediators... 

Triethylene glycol divinyl ether (donor) — maleimide (acceptor) 1,4-Cyclohexane dimethanol divinyl ether (donor) — alkyl maleimide... 

The two general modes of colloidal stabilization are electrostatic (left) and steric (right). In the electrostatic mode there is a bilayer of anions (often halides) and a second layer of cations (for example tetra alkylammonium). In the steric stabilization there is a single bulky molecule attached to the surface (usually a P, N, or S donor, alkyl thiols are common). 

C. Complexes with [Pg.199]

In actual practice, there are, of course, many complexities superimposed on this basic mechanism of cationic polymerization. Many of the catalyst systems consist of two components. In some systems, for example, BF3 is an effective catalyst only in the presence of some water. It may be that the active catalyst is the adduct, which serves as a proton donor. Alkyl halides in combination with Lewis acids can also... 

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