New Developments in the Field of Photochemical Syntheses

This survey highlights part of the rapidly increasing number of preparatively valuable photochemical methods for natural products synthesis. Applications based on [2 + 2] cycloadditions - C-C bond and oxetane formation, olefin-to-arene meta-cycloadditions, and oxadi-π-methane rearrangements - are discussed with regard to efficiency, generality, and selectivity. The majority of these light-induced transformations proceed at high levels of chemo- and stereocontrol upon proper choice of the wavelength of excitation. This particularly important but frequently neglected parameter can be satisfactorily tuned in preparative runs in most cases. Furthermore, attention is paid to asymmetric induction and the preparation of enantiomerically pure products. 1 . Introduction 2. [2+2] Cycloadditions 2.1. [2+2] Cycloadditions of Alkenes, Allenes, and Alkynes to α,β-Unsaturated Carbonyl Compounds Forming C-C Bonds 2.1.1. Regioselectivity 2.1.2. Stereoselectivity 2.1.3. Asymmetric Induction 2.1.4. Applications 2.2. Oxetane Formation via [2+2] Cycloaddition: The Paternó-Büchi Reaction 2.2.1. Regio- and Stereoselectivity 2.2.2. Asymmetric Induction 2.2.3. Applications 2.3. [2+2] Cycloadditions of 1,3-Dienes to α,β-Unsaturated Ketones and Related Chromophores Forming C-C Bonds 3. Olefin-to-Arene meta-Cycloaddition 4. Oxadi-π-methane Rearrangement 4.1. General Aspects. The Basic Reactive Substrates 4.2. Preparation of Enantiomerically Pure Products 4.3. Applications 5. Further Topics of Current Interest in the Field of or Related to Photochemical Syntheses