Partial access scheme

If a perfect memory property could be realized, the refreshing process would not be necessary. Only by a partial access scheme could a higji contrast ratio be obtained. On the other hand, in the case of SSFLCs with a poor memory property, the refreshing process must be carried out frequently, and the number of scanning lines would be limited. For SSFLCs, memory property determines both the number of scanning lines and the contrast ratio. 

The scheme below shows reaction possibilities for carbonyldiimidazole activation of polyhydroxylic matrices. The formation of these activated sites depends on[117] 1. the partial disposition of hydroxyl groups accessible to the solvent, 2. the initial concentration of CDI, and 3. the chemical nature of the gel matrix. 

Since ketone R)-16 was prepared in a non-selective way when an achiral imino enolate was alkylated, it was considered whether alkylation of chiral enolates, such as that of oxazoline 18, with benzyl bromide 14, would provide stereoselective access to the corresponding alkylation product 19 with R-configuration at C(8) (Scheme 4). Indeed, alkylation of 18 with 14 gave the biaryl 19 and its diastereoisomer almost quantitatively, in a 14 1 ratio. However, reductive hydrolysis using the sequence 1. MeOTf, 2. NaBH4, and 3. H30", afforded hydroxy aldehyde 20 in 25% yield at best. Furthermore, partial epimerization at C(8) occurred (dr 7.7 1). An alternative route, using chiral hydrazones, was even less successful. 

The Richardson-Hough research partnership also observed that, if the quantity of pivaloyl chloride was raised to 7 equivalents and similar reaction conditions were applied, access to a partially pivaloylated trehalose having the 3- and 4 -hydroxyl groups free was gained in 38% yield, together with a symmetrical 2,3,6,2 3, 6 -hexapivalate, which was formed in 31% yield (Scheme 18). 

Under appropriate conditions, the perfluorocarbon (CF3)3CCF2CF2-C(CF3)3is obtained in 89%yield (70b). As may be seen from the reaction scheme, a number of partially fluorinated products are also isolable and it is clear that the protons are readily accessible to fluorine. The physical properties of highly branched fluorocarbons (see Table IX) are most unusual. 

Strained and polymerizable cyclotetrasilanes Si4Me Phg (n = 3,4,5,6) are accessible by the partial dearylation of octaphenylcyclotetrasilane and subsequent displacement with MeMgBr49. l,2,3,4-Tetramethyl-l,2,3,4-tetraphenylcyclotetrasilane, for instance, is formed by the reaction of (SiPh2)4 with 4 equivalents of triflic acid followed by treatment with 4 equivalents of methyl magnesium bromide. Three of the four possible isomers are obtained in a ratio of la lb lc = 45 15 40, whereas the all-a. v-i sorrier Id has not been observed (Scheme 8). Recrystallization from cold hexane yields isomer la in 95% purity53. 

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