Photo-induced Cycloaddition Reactions Of α-Dicarbonyl Compounds And Their Synthetic Applications

Photo-induced cycloadditions of carbonyl compounds with C=C containing substrates, along with subsequent cascade reactions, have provided expeditious way to construct diversified organic framework. The main purpose of this dissertation is to report unusual photo-induced reactions of α-dicarbonyl compounds with alkenes and the follow conversion of the cycloadducts to construct special lactone structures. The main work included in this dissertation is described in the following three parts:1. Photo-induced reactions of a-dicarbonyl compounds including substituted isatin especially N-acetylisatin and N-methyl-1,3,4-isoquinolinetrione with bicycloalkylidenes including bicyclopropylidene, bicyclohexylidene, cyclopropylidenecyclobutane and cyclopropylidenecyclohexane were investigated. Except for the conventional spirooxetane products derived from the Paterno-Buchi cycloaddition of the C=O and C=C, unusual products such as the [4+2] or [4+2+2] cycloadducts and other ring-rearranged products were also obtained in these reactions. The distribution of various type of products was relevant to the involvement of oxygen, which was investigated in detail through comparison on the photoreactions proceeded under N2and O2atmosphere. The extra strain presented by the cyclopropyl ring on the double bond was the major reason for the unusual photo-reactivity of the cyclopropylidenecyclanes. 2. The [2+2] cycloadducts spirocyclopropyl oxetanes (SCOs) which were the major products of photoreactions between functionalized isatin and alkylidenecyclopropanes could undergo versatile transformations under various acidic conditions. HCl (or HBr) and HI mediated these SCOs transformation could electively give spirocyclopropyl substituted butenolides and y-lactones which are both versatile synthetic intermediate and structural component in many natural products respectively. BF3'OEt2could catalyze the cascade reactions of SCOs to afford diversity products depend on the solvent. The reaction mechanism leading to these products has been also proposed by detailed studies on the acid-mediated transformations of SCOs.3. We developed a facile photochemical approach to biaryl-containing medium-ring bislactones with easily available reactants including phenanthrenequinone and alkenes via a concise photocycloaddition-photooxidation sequence. This approach involved two steps, the first step was the photo-induced [4+2] cycloaddition of the o-dione with C=C bond to form the dioxinophenanthrene or dioxinophenanthroline. Further transformation of the dioxinophenanthrene or dioxinophenanthroline into the biphenyl or bipyridine-containing medium-ring bislactones proceeds rapidly upon photoirradiation under oxygen atmosphere. The approach was highly atom-economic in that no catalysts or additional photosensitizers were needed in the reaction sequence and the biaryl containing medium-ring bislactones could be easily prepared with good yields and diastereoselectivity.