3,3,6,6-Tetraalkyl-substituted

Isopropyl-4,5,6-fm-butylpyridazine, which exists in the twist conformation, is transformed upon photolysis into the corresponding 1,2-Dewar-pyridazine, which is stable (91AG1495). Irradiation of the ketone 179 with UV light produces about 10% of 180 (92JA1838). Photooxidative decomposition of 3,3,6,6-tetraalkyl-substituted perhydropyridazines was investigated and it was found that decomposition is stereospecific and that the 1,4-biradical determined the stereochemical outcome and not the 1,4-cation radical. Cyclobutane and 1-butene derivatives were products identified (93JA4925). 

The dipolar ion can react in several ways according to the solvent and the stmcture of the olefin. In inert solvents, if the carbonyl compound is highly reactive (eg, an aldehyde), the dipolar ion can be added to the carbonyl fragment to give the normal ozonide or 1,2,4-trioxolane (7) for example, 1,1-and 1,2-dialkylethylenes react in this manner. Tri- or tetraalkyl-substituted olefins produce a smaH, if any, yield of an ozonide when the ozonolysis is... 

Example IV The thermal and oxidative isomerization of tetraalkyl-substituted tetrahedrane clusters (CR)4 to cyclobu-tadienederivatives. 

Example IV The Thermal and Oxidative Isomerization of Tetraalkyl Substituted Tetrahedrane Clusters to Cyclobutadiene Derivatives. Other remarkable structural changes during redox reactions, i.e. charge redistributions enforced by the respective energy differences, are observed for cluster compounds (1). On... 

Generally, tetraalkyl-substituted double bonds react at faster rates than do trialkyl-substituted double bonds, which in turn react faster than dialkyl-substituted ones.104,135 Relative reactivities can be determined from the experimental fi values (/S = k8/k9) since ke is a constant as long as the experiments are carried out under the same conditions.61... 

C=C Stretching Vibrations Unconjugated Linear Alkenes The C=C stretching mode of unconjugated alkenes usually shows moderate to weak absorption at 1667-1640 cm1. Monosubstituted alkenes, that is, vinyl groups, absorb near 1640 cm-1, with moderate intensity. Disubstituted trans-alkenes, tri- and tetraalkyl-substituted alkenes absorb at or near 1670 cm-1 disubstituted ds-alkenes and vinylidene alkenes absorb near 1650 cm-1. 

In general, tetraalkyl-substituted double bonds react at a faster rate than do trialkyl-substituted double bonds, which in turn react faster than dialkyl-substituted ones. 

The preparation of other branched triangulanes with varying symmetries has also been reported. A notable feature of this series of small hydrocarbon cascades is that the framework is composed entirely of quaternary, tetraalkyl-substituted carbons. This unique architecture closely resembles or is at least reminiscent of Maciejewski s 16 proposed cascade molecule comprised of an all 1 — 3 C-branched interior framework (i.e., without spacers between branching centers). 

Scheme 4.51. Dendrimers prepared using tetraalkyl substituted silicon, as branching centers.

Cyclobutanes may be converted to alkenes thermally, the reverse of the [2 + 2] cycloaddition reaction. These retroaddition or cycloreversion reactions have important synthetic applications and offer further insights into the chemical behavior of the 1,4-diradical intermediates involved they may proceed to product alkenes or collapse to starting material with loss of stereochemistry. Both observations are readily accommodated by the diradical mechanism. Generation of 1,4-tetramethylene diradicals in other ways, such as from cyclic diazo precursors, results in formation of both alkenes and cyclobutanes, with stereochemical details consistent with kinetically competitive bond rotations before the diradical gives cyclobutanes or alkenes. From the tetraalkyl-substituted systems (5) and (6), cyclobutane products are formed with very high retention stereospecificity,while the diradicals generated from the azo precursors (7) and (8) lead to alkene and cyclobutane products with some loss of stereochemical definition. ... 

Strained -oxidoalkyl i enyl selenoxides, such as l-oxido-l-(r-phenylsdenoxyalkyl)cyclopropanes, derived from oxaspiropentanes with tetraalkyl-substituted oxirane rings, and l-(r-hydroxyalkyl)-l-selenoxycyclobutanes, - obtained on oxidation of the corresponding selenides or on reaction of a-li-thioalkyl selenoxides with cyclobutenones, possess a high propensity to rearrange to cyclobutanones... 

Another limitation of this procedure occurs in the case of tetraalkyl-substituted dibromocyclopropanes they do not yield allenes, but rather bicyclobutanes (Scheme 72). However, tetrasubstituted dibromocyclopropanes with two aryl substituents do give allenes, at least as a by-product. 

Table 1 C and N chemical shifts (ppm) of tetraalkyl substituted and cyclic thiuram disulfides and initial sodium dithio carbarn ate salts [relative to TMS (i C) and NH4CI ( = N)]... 

With 1 as catalyst, alkene bonds which have oxidation potentials less than 1.6 V (vs standard calomel electrode) are considered potentially susceptible to this transformation. With the stronger oxidant 2, the scope of the reaction can be extended to include, for example, tetraalkyl-substituted double bonds, but obviously not disubstituted alkenes such as cyclohexene. On the other hand, electron-rich alkenes such as enol ethers and vinyl sulfides cannot be cyclo-propanated by this method. In order to suppress cyclodimer formation from the alkene and its radical cation, the diazo ester is sometimes applied in a four- to fivefold amount with respect to the alkene. 

Reaction of 142 with trimethylsilyl cyanide and allyltrimethylsilane under SnCl4 catalysis yields the tris(cyanide) 147 and the tris(allyl)tribenzotri-quinacene 148 [98]. Substitution of the bromine atoms takes place very efficiently by treatment of 142,145 and 146 with trimethylaluminum, to give trime-thyltribenzotriquinacene 149 and the tetraalkyl-substituted analogues 150 and 151, respectively, in excellent yields (>90%) [100]. Whereas reaction of 142 with triethylaluminum gives rise to complete reduction to 7, use of ethylmagnesium bromide affords 152 in low (20%) yield. A variety of further carbon-bonded sub-... 

A. iV -ditosyl-substituted, 41. 126, 180. 258 hydroxymethyl-substituted, 249. 250 on sorbents, 20, 21 tetraalkyl-substituted, 260 Diaza-19-crown-6 macrocycles allyloxymethyl-substituted, 260 bis(hydroxymethyl)-substituted. 259 methylene-substituted. 260 oxetano-substituted, 259 Diaza-20-crown-6 macrocycles, bisoxetano-substitutcd, 261... 

It has been also reported sicne 1958 [52] that itaconic anhydride (lAn), which is an another cyclic derivative of lA, polymerizes as well as other lA derivatives, but its reactivity is less than those of RII and RPhll. Poly(IAn) may be derived into some poly(IA) derivatives by reaction with amines and alcohols [63,64]. The polymerization reactivities of several itaconamides (lAm) and itaconamates (lAE) were also investigated [48]. It was found that iV, -dialkyl substituted lAm homopolymerize in the presence of a radical initiator, but iV,iV,iVj -tetraalkyl-substituted one did not give a polymer, because the latter consists of an a,7V, trisubsti-tuted acrylamide structure resemble to, y disubstituted methacrylamides. Similar results were obtained for polymerization of mono- and, V disub-stituted lAE. 

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