In this study, the isothiourea-catalyzed enantioselective formal [4+3] cycloaddition of various α,β-unsaturated carboxylic acid derivatives with 2-aminothiophenols was developed. Mechanistic studies suggested that the reaction proceeds via a reversible sulfa-Michael addition to α,β-unsaturated acylammonium intermediates, followed by the enantioselective formation of a seven-membered ring, enabling the facile and divergent synthesis of optically active 2- and 3-substituted 1,5-benzothiazepines. This process was demonstrated to be highly versatile, affording the corresponding products in excellent regioselectivities and high enantioselectivities. Furthermore, this method enabled the synthesis of chiral 2,3-disubstituted 1,5-benzothiazepines in high regio-, enantio-, and diastereoselectivities. Hence, this protocol can be applied for the construction of a library of useful pharmaceutical candidates.

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Poly(vinyl alcohol) (PVA) hydrogels were prepared by the repeated freezing and thawing cycles, and creep behavior of the gels was examined. In the gel preparation, the salt K 2 CO 3 was introduced to obtain the clear gel structure. By the creep we also prepared the condensed PVA gels with unidirectional structure. The mechanical anisotropy was observed for the unidirectional gel.

We have compared the experimental results on solvent squeeze from cylindrical poly(vinyl alcohol) (PVA) gels with the model presented in this paper. The model says that a characteristic time for solvent squeeze, which is also a retardation time of the creep of gels, is proportional to the diameter squared. A simplified version of the model, which is valid when the creep strain is small enough, indicates that retardation time is independent of the applied stress and the height of gels approaches to a constant value in a single-exponential manner. Experiments on PVA gels say that the change in height occurs almost in a single-exponential manner. The retardation time was independent of the applied stress at small stresses but became longer in the high stress region, as in the case of the presented model. The diameter dependence of the retardation time for the PVA gels was weaker than the model prediction. As a whole, the simplified version of the model is useful to explain the squeezing behavior of the PVA gels.