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p-TsOH promoted annulation reaction of 3-(indol-3-yl)maleimides and (indol-2-yl)diphenylmethanols in chloroform afforded functionalized pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles in satisfactory yields, in which a formal [4+3] cycloaddition and an unprecedented rearrangement of the maleimide motif from the C3- to C2-position of the indole ring was firstly observed. Alternatively, the similar reaction of 3-(indol-3-yl)maleimides and 3-hydroxy-3-(indol-3-yl)-indolin-2-ones in acetonitrile gave functionalized spiro[indoline-3,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indole] in good yields and with high diastereoselectivity. On the other hand, p-TsOH promoted reaction of 3-(indol-3-yl)maleimides and 2-hydroxy-2-(indol-3-yl)-indene-1,3-diones gave functionalized spiro[indene-2,9′-pyrrolo[3′,4′:4,5]cyclopenta[1,2-b]indoles] as major products and spiro[indene-2,9′-pyrrolo[3′,4′:6,7]cyclohepta[1,2-b:4,5-b′]diindoles] as minor products. [ABSTRACT FROM AUTHOR]

Triethylamine promoted cycloaddition reaction of phenacylmalononitriles and o-hydroxychalcones in ethanol at room temperature gave multifunctionalized cyclopent-3-ene-1-carboxamides in good yields and with high diastereoselectivity. More importantly, the similar reaction of phenacylmalononitriles and chalcone o-enolates in ethanol at room temperature afforded functionalized 2-oxabicyclo[2.2.1]heptane derivatives in satisfactory yields and with high diastereoselectivity. A rational domino reaction was tentatively proposed to explain the selective formation of different cyclic compounds and the diastereoselectivity of the reaction. [ABSTRACT FROM AUTHOR]

Photochemical reactions are vital synthetic means for the synthesis of natural products and highly strained molecules. However, it remains an immense challenge to control the chemo- and regioselectivity in the photoreactions of anthracene derivatives while maintaining high reactivity. Herein, we report the synthesis of two photoactive metallarectangles 1a and 1b by coordination-driven self-assembly of 2,6- and 2,7-bifunctionalized anthracenes with a half-sandwich rhodium template. By taking advantage of the rhodium template, the anthracene groups within the metallarectangles can be preorganized in a parallel fashion and exclusively undergo a photochemical [4 + 4] cycloaddition. As a result, the syn-photodimers were obtained in quantitative yields under irradiation at 365 nm. The photocycloaddition of metallarectangles 1a and 1b was found to be reversible via photo- and thermal cleavage reactions, even after repeating three times. Furthermore, pure organic photodimers 3a and 3b, which are difficult to synthesize by conventional organic methods, can be readily dissociated from the metalloassemblies in high yields. [ABSTRACT FROM AUTHOR]

A facile synthetic method to form cage-annulated crown ether with anchored imidazolium units was developed. The present work verified the potential application of the metal–carbene template approach (MCTA) in the preparation of novel flexible polyimidazolium cages by photochemical [2+2] cycloaddition reactions and may provide a new method for the preparation of flexible pure organic cages with incorporation of a variety of functional sites. [ABSTRACT FROM AUTHOR]

TEMPO promoted cycloaddition reaction of different kinds of ketohydrazones or aldohydrazones with 3-phenacylideneoxindoles showed very interesting molecular diversity according to the chemical structures and reaction conditions. The reactions with 1-(3,4-dihydronaphthalen-1-ylidene)-2-arylhydrazines or 1-cyclohexylidene-2-arylhydrazines in acetonitrile at 80 °C afforded functionalized spiro[benzo[h]cinnoline-3,3′-indolines] or spiro[cinnoline-3,3′-indolines] via aza-Diels–Alder reaction of the in situ generated 1,2-diaza-1,3-diene. The reactions with 2-(2-phenylethylidene)-1-arylhydrazines in dioxane afforded functionalized spiro[indoline-3,3′-pyrazoles] though a [3+2] cycloaddition reaction of the in situ generated 1,3-dipolar azomethine imine. On the other hand, a similar reaction in acetonitrile unusually resulted in pyrazole derivatives via sequential [3+2] cycloaddition and a ring-opening process. [ABSTRACT FROM AUTHOR]

Solid-state multiple [2 + 2] cycloaddition reactions of polyenes continue to attract attention as a mediate for the synthesis of polycyclobutane derivatives. The solid and crystalline states of polyenes restrict molecular movements of C＝C bonds and, as a result, contribute to the selective formation of polycyclobutane derivatives through photochemical [2 + 2] cycloaddition reactions. In this review, functionalised polyenes preorganised by suitable templates, such as muconate and 4-pyr-poly-2-ene (ppene) derivatives, are summarised and their multiple [2 + 2] cycloaddition reactions are described, which lead to the generation of polycyclobutane derivatives in the solid state. Single-crystal-to-single-crystal (SCSC) transformations in which the single-crystal character is preserved along the reaction sequence are emphasised, as they provide unambiguous information regarding the structural changes during the reaction. [ABSTRACT FROM AUTHOR]