J. Appl. Cryst.の発刊に際して

2.3. [4 + 4] Cycloadditions 1058 2.4. Photocycloadditions of Aromatic Compounds 1058 2.4.1. Benzene Derivatives 1058 2.4.2. Condensed Aromatic Compounds 1060 3. Photochemical Rearrangements 1061 4. Cyclizations 1064 4.1. Pericyclizations 1064 4.2. Norrish−Yang Reaction 1066 5. Photochemical Extrusion of Small Molecules 1067 6. Photochemical Electron Transfer 1068 6.1. Photochemical Electron-Transfer Reactions with a Catalytic Sensitizer 1068

Photochemical Reactions as Key Steps in Organic Synthesis

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00723

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2+2] Photocycloaddition Reactions

Natural and synthetic cyclopropanes bearing simple functionalities are endowed with a large spectrum of biological properties ranging from enzyme inhibitions to insecticidal, antifungal, herbicidal, antimicrobial, antibiotic, antibacterial, antitumor and antiviral activities.

Cyclopropane Derivatives and their Diverse Biological Activities

9-Hydroxymethylcyclopropylidenemethylenyladenine: The design, facile synthesis, isomer separation and anti-HIV-1 activities

Photochemical reactions of three kinds of 1-(ω-alkenyl)-2-pyridones 1-8 were investigated. Photosensitized cycloadditions of 1-(ω-alkenyl)-2-pyridones and 1,3-bis(ω-alkenyl)-2-pyridone 2-6 afforded intramolecular [2+2]cycloadducts across the 5,6-bonds of the 2-pyridones to give the tricyclic lactams 14-18: the additions were site-, regio-, and stereospecific. The yields of the adducts diminshed in proportion to increased side-chain length

Intramolecular [2 + 2]photocycloadditions of 1-(.omega.-alkenyl)-2-pyridones possessing an ester group on the olefinic carbon chain

Substituent effects on the regiochemistry of enone-alkene 2+2-photocycloadditions. experimental results and fmo analysis

The skeleton of the 2-pyrones (1) is a simple one composed of 2,4-pentadien-5-olides, but has many possibilities for photocycloadditions. To elucidate the peri-, site-, and regioselective photoadditions of the triplet 2-pyrones with some ethylenes, the factors were analyzed by PM3-CI-UHF methods, etc. The regioselective [4+2]cycloadducts (3) and site-selective [2+2]cycloadducts (4) across the C5–C6 double bonds of the 2-pyrones with electron-deficient ethylenes were deduced to be formed by their preferable HSOMO–LUMO interactions and via more stable biradicals by the C6-Cβ bondings. On the other hand, the other kinds of regioselective [4+2] (6) and [2+2]adducts (5) across the C3–C4 double bonds of the 2-pyrones with an electron-donating ethylene were inferred to mainly come from LSOMO–HOMO interactions and via biradicals by C3-Cβ bondings. Selectivities between 3 and 4, and 5 and 6 were also inferred to be caused by SOMOs of the biradicals.

Tetsuro Shimo

Papers

9-Hydroxymethylcyclopropylidenemethylenyladenine: The design, facile synthesis, isomer separation and anti-HIV-1 activities

Intramolecular [2 + 2]photocycloadditions of 1-(.omega.-alkenyl)-2-pyridones possessing an ester group on the olefinic carbon chain

Substituent effects on the regiochemistry of enone-alkene 2+2-photocycloadditions. experimental results and fmo analysis

MO Analysis of Photocycloaddition Reactions of 2-Pyrones

Intramolecular photocycloadditions of 6,6′‐dimethyl‐4,4′‐polymethylenedioxy‐di‐2‐pyrones