Copper(II)-catalyzed hydroxylation of aryl halides has been developed to afford functionalized phenols. The protocol utilizes the reagent combination of Cu(OH)2, glycolic acid, and NaOH in aqueous DMSO, all of which are cheap, readily available, and easily removable after the reaction. A broad range of aryl iodides and activated aryl bromides were transformed into the corresponding phenols in excellent yields. Moreover, it has been shown that C-O(alkyl)-coupled product, instead of phenol, can be predominantly formed under similar reaction conditions.

Theoretical and experimental studies were investigated on the growth characteristics and electrical properties of HfO2 films using Hf(N(CH3)2)4 and CpHf(N(CH3)2)3.

With the hope of mimicking the chemical and biological properties of natural 6-O-methyl-Dglucose-containing polysaccharides (MGP), synthetic 6-O-methyl-D-glucose-containing polysaccharides (sMGP) were designed and synthesized from α-, β-, and γ-cyclodextrins (CDs). The synthetic route proved to be flexible and general, to furnish a series of sMGPs ranging from 6-mer to 20-mer. A practical and scalable method was discovered selectively to cleave the CD derivatives and furnish the linear precursors to the glycosyl donors and acceptors. The Mukaiyama glycosidation was adopted to couple the glycosyl donors with the glycosyl acceptors. Unlike in the sMMP series, an amount of the Mukaiyama acid required in the sMGP series increased with an increase of substrate size; for large oligomers, more than one equivalent of the acid was required.

Glycosidation of a mannosyl donor in the presence of the Mukaiyama catalyst was found to give exceptionally high alpha/beta selectivity. A systematic study was conducted to reveal that selective beta-to-alpha anomerization accounts for the observed high alpha/beta stereoselectivity. Furthermore, the Mukaiyama catalyst was shown to exhibit an unusual level of substrate and anomer selectivity for the anomerization. On the basis of the combined anomeric and delta2 effects, a mechanistic rationale was proposed, thereby suggesting the minimum structural moiety essential for the anomerization in question. With this analysis, beta-talo-, beta-altro-, and beta-idopyranosides are predicted to exhibit a reactivity profile similar to beta-mannopyranosides, but all other pyranosides should not. This prediction was verified by using beta- and alpha-talopyranosides as an example.

A second-generation synthesis of synthetic 3-O-methyl-D-mannose-containing polysaccharides (sMMPs) is reported. The glycosidation of donor B and acceptor C, prepared from a common precursor A in two and one steps, respectively, is effected by t-butyldimethylsilyl trifluoromethanesulfonate to furnish only the desired alpha-anomer D in high yields. Unlike the first-generation synthesis, this synthesis gives the desired product free from contamination of scrambling products. A three-step protocol is used to deprotect D to furnish sMMPs.

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In connection with an ongoing program in this laboratory, we synthesized tetraenoic fatty acids (TE-FAs) [1] as a probe [2] for the study of association/dissociation events between fatty acids (FAs) and synthetic 3-O-methyl-d-mannose-containing polysaccharides (sMMP) [3,4] and synthetic 6-O-methyl-d-glucose-containing polysaccharides (sMGP). [4,5] During spectroscopic characterization of TE-FAs, we observed an interesting phenomenon: C 20 -t,t,t,t-TE-FA (1 c) exhibits an expected UV absorption at 303 nm with fine structure in methanol but a dramatically different UV absorption at 250 nm without fine structure in aqueous solution (Figure 1 A).The observed blue shift in the UV absorption appeared to be associated with aggregation of 1 c in buffer solution. Aggregate formation is driven by hydrophobic interaction and is dependent on the polarity of solvents. Figure 1 B shows overlaid UV spectra of 1 c in buffer containing an increasing amount of methanol. As expected, with the increase of methanol content the unique UV absorption at 250 nm changed to the normal absorption of tetraene with fine structure. Similarly, the UV experiment demonstrated that aggregate formation of 1 c is concentration-dependent, with the estimated threshold concentration of aggregation being approximately 0.3 mm.[6] Lastly, sMMP and sMGP were shown to form a 1:1 complex with 1 c in aqueous solution, resulting in disaggregation and bringing the blue-shifted UV absorption back to the normal absorption of tetraenes. [6,7] These results support the view that the blue-shifted UV absorption of 1 c in aqueous solution is indeed associated with aggregation.The examples known in the literature suggest that the observed blue-shifted UV absorption may be attributed to an H-aggregation of 1 c in buffer solution. An H-aggregate contains a card-pack orientation of 1 c, and according to exciton theory [8] the H-aggregate excitonic splitting results in a high-energy allowed transition and a low-energy forbidden transition (Figure 2). Thus, the UV absorption of 1 c is blueshifted. Related to this work, we should specifically mention that Whitten and co-workers have shown that FAs which incorporate various chromophores form H-aggregates characterized by a blue-shifted UV absorption. [9,10] With the unique observations on C 20 -t,t,t,t-TE-FA (1 c), we selected TE-FAs 1 a-f and 2 a-c systematically to study the effects of chain length and tetraene geometry on aggregation behaviors.[1] All the TE-FAs exhibited the expected UV absorption with fine structure in methanol (1 a-f: l max % 300 nm; 2 a-c: l max % 304 nm). The unique blue-shifted UV absorption was observed for the C 20 (1 c),