4,4-Dimethyl-Diox

It has already been observed in the polymerization of substituted E-caprolactams 1 1, that the substitution of hydrogen atoms decreases the polymerizability of monomers. The same phenomena were observed in the polymerization of 4,4-dimethyl-, cis-4,5-dimethyl and trans-4,5-dimethyl-Diox 15. ... 

Studies have established that the partition between transition states 3 and 4 depends on the nature of the diol unit bound to boron and on the steric and electronic effects of the a-sub-stituent X23. The data shown below demonstrate that the reactions of2-(l-methyl-2-propenyl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane proceed with a moderate preference for transition state 3 with the C2 methyl group in an axial position. Selectivity diminishes with 2-(l-methyl-2-propenyl)-l,3,2-dioxaborolane and reverses with dimethyl (l-methyl-2-propenyl)boronale, suggesting that steric interactions (gauche interactions in the case of the tetramethyl-1,3,2-diox-aborolane) between X and the diol unit on boron are capable of destabilizing transition state 4 relative to 3. 

S,5S)-5-(2-Alkeny/ideneamiuo)- or (4S,5S)-5-(2-Alkynylideneamino)-2,2-dimt lli)l-4-phenyl-l,3-clioxane 8 Equimolar amounts of an a,/f-unsaluraled aldehyde and (45,55 )-5-amino-2.2-dimethyl-4-phenyl-1,3-diox-ane 7 are mixed with cyclohexane and refluxed for 2 h using a Dean-Stark trap. Then the cyclohexane is removed, the residue is dissolved in Ei,0 and dried over MgSO . Evaporation of the solvent provides imine 8 yield. 90-98%. 

Benzoxadiazole 1-oxide (481) with 3-acetyltetrahydro-2-furanone (2-acetyl-butyrolactone 482) gave 2-(2-hydroxyethyl)-3-methylquinoxaline 1,4-diox-ide (483) (KOH, MeOH-HaO, 20°C, 24 h 50%) but with 2-acetylacetaldehyde dimethyl acetal (484), in the presence of morpholine as base, it gave 2-(2-morpholinovinyl)quinoxaline 1,4-dioxide (485) (PhH, reflux, water separation, 9 h 47%) ... 

Formed by fluorine oxidation of the dilithium salt of hexafluoroacetone hydrate, it is unstable and explosive. The chloropentafluoro homologue is similar. Proponents of their use as reagents claim that the dimethyl and methyltrifluoromethyl analogues are not explosive this seems improbable, especially since the less stressed lower dioxe-tanes (homodioxiranes) are all dangerous. 

Leismann et al.[182] have recognized this problem in their publication of 1984, in which they describe a thorough and detailed investigation of the kinetics of formation and deactivation of exciplexes of. S) benzene or toluene and 1,3-diox-ole, 2,2-dimethyl-l,3-dioxole, and 2,2,4-trimethyl-l,3-dioxole. The evolution in time of monomer and exciplex fluorescence after excitation using a nanosecond flash lamp was analyzed, and again it was concluded that the formation of exciplexes is diffusion controlled their decay proceeds mainly (>90%) via radiationless routes. The polar solvent acetonitrile enhances radiationless deactivation, possibly by promoting radical ion formation. Because decay of benzene fluorescence is essentially monoexponential, dissociation of the exciplex into Si benzene and dioxole is negligible. 

Solvents shown were those used for the determination of kSSN kH20,SN determined in H2O, unless otherwise specified. Numbers in parentheses are the volumetric proportions for solvent mixtures. Abbreviations are as follows MeOH methanol ace acetone diox dioxane EtOH ethanol DMF dimethylformamide DMSO dimethyl sulfoxide. Solvent not specified when value of log(ks/kH2o)sN was estimated solely from a correlation equation (e.g., those provided in (181 and (22)). 

Dimethyl-2,6-diox o-8-hydrazino-1 -(2-hydroxy-propyl)-1,2,3,4-tetrahydro- E16a, 684 (Br - NH-NH2)... 

Dimethyl-2,6-diox o-l-isopropyl- E14a/2, 306 (Keten + Imin)... 

Qeavage of the A "-Dde and N"-l-(4,4-dimethyl-2,6-dioxocyclohexylidene)-3-methylbutyl groups is performed with 2% anhydrous hydrazine or hydrazine hydrate in DMF at room temperature (on resin, 3 x 2min). This leads to a l,5,6,7-tetrahydro-4//-indazol-4-one 25 as the byproduct (Scheme 10), which can be monitored by UV spectroscopy at 220 or 290 nm.O Since hydrazine will also remove Fmoc groups, the assembly of the peptide by Fmoc/tBu chemistry must be completed prior to the cleavage of the Dde or l-(4,4-dimethyl-2,6-diox-ocyclohexyhdene)-3-methylbutyl groups. 

IrCI02P4C jH32, Iridium(l-t-), (carbon-diox-ide)bis[ 1,2-ethanediyIbis(dimethyl-phosphine)]-, chloride, 21 100... 

CYCLOADDITION Alumina chloride. l,2-Bis(trimethylsilyloxy)cyclo-butene. 2,2-Dimethyl-3(2/T)-furanone. Ethylaluminum dichloride. Ketene diethyl acetaL Methyl cyclobutene-carboxylate. Trimethyl-1,3-diox olen-one. Zinc chloride. 

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