“Polyunsaturated” Cyclophanes

Abstract

Cyclophane chemistry has a long and colorful history. [1] Although this discipline has evolved in many ways, several of the fundamental sources of interest in cyclophanes remain unchanged. These include the conception of novel, aesthetically pleasing and interesting structures, the challenge of synthesizing them, and the study of their properties once they have been prepared.As with other areas of synthetic chemistry, the development of new methodology has played a crucial role in the development of cyclophane chemistry. An early example of this is the emergence of the sulfur-based ring-contraction strategies that were developed in the 1960s and 1970s, [2] which paved the way for the synthesis of a very wide range of [2.2]cyclophanes and [2.2]cyclophanedienes. That these approaches are still in use today speaks to their lasting value. A more recent example is the advent of palladium-catalyzed cross-coupling reactions, [3] which opened the door for the design and synthesis of whole new families of cyclophanes, that is, those that have multiply unsaturated bridges. A selection of such ™polyunsaturated∫ cyclophanes is presented in Scheme 1.When considering compounds that are composed of aromatic units linked by unsaturated bridges, the distinction between a cyclophane and a dehydrobenzannulene (DBA) can become blurred, or even disappear entirely. A crude criterion for distinguishing these two fascinating classes of compounds is that a DBA has only 1,2-disubstituted aromatic units, whereas a cyclophane has at least one non-1,2-disubstituted aromatic unit. [4] Thus, the aptly named ™dehydrobenzannulene ± dimethyldihydropyrene hybrid∫ 1 reported by Haley, Mitchell, falls under the DBA category, whereas the ™[2.2]paracyclophane-dehydrobenzannulene hybrids∫ 2 and 3 described by Hopf, Haley, and coworkers [6] fall under the heading of cyclophanes. Comparison of the electronic absorption spectra of 2 and 3 with appropriate DBAs and ™broken∫ DBA analogues provided 1 2 3Scheme 1. Some examples of cyclophanes with multiply unsaturated bridges, made by using palladium-catalyzed cross-coupling.

Enantioselective Total Syntheses of Several Bioactive Natural Products Based on the Development of Practical Asymmetric Catalysis

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Van Der Waals Interactions and the Hydrophobic Effect

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A reação de Diels-Alder no início do século vinte um

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