A Study Towards C-O Bond Cleavage With C-Br And C-C Bonds Formation

The thesis mainly consists of the following two parts:Part Ⅰ: A mild and efficient method for bromination of alcohols usingα,α-dibromo-β-dicarbonyl compounds as halogen sourcesAlkyl halides are valuable compounds with a wide range of applications in daily life, itcan be used as narcotics, refrigerant, pesticides, etc. As one of the most common andsignificant building blocks in organic synthesis, it also can be applicated in carbon-carbon andcarbon-heteroatom bonds formation reactions, such as Wurtz coupling and Buchwald-Hartwigcross-coupling reactions. The transformation of alcohols to the corresponding halides is oneof the most widely used reactions in organic synthesis. Over the past decades, severalmethods have been developed for this transformation, making use of various halogenatedreagents including thionyl chloride, Vilsmeier-Haack reagent, etc. Among them, the Appelreaction, which uses combined systems of PPh3with a halogen source is found to be the mostutilized method in organic synthesis due to its convenience and mildness. However, thehalogen sources for this reaction is rather limited and toxic such as CCl4and CBr4. In order tomodify theses methods, further exploration of new halogen sources for efficient preparationof alkyl halides under neutral conditions would be desirable. In this paper, the exploration ofα,α-dibromo-β-dicarbonyl compounds as novel bromine agents for the transformation ofalcohols to alkyl bromides under neutral conditions has been achieved. The high reactivity ofthese compounds allows the bromination of various primary and secondary alcoholsproceeding at room temperature within a very short period of time. This reaction system canalso be used for acid-sensitive substrates.Part Ⅱ: Iron-Catalyzed C-O Etheric Bond Cleavage with C-C and C-H BondsFormationCarbon-carbon bond formation is an attractive strategy in terms of both the accessibilityof the starting materials and environmental concerns in organic synthesis. Ethers havegarnered much attention over the past decades as novel electrophiles in the transition-metalcatalytic activation of etheric C-O in C-C and C-N bond formation reactions, since they havemany apparent advantages from environmental and economical viewpoints compared with thecorresponding halides. In contrast to the considerable efforts devoted to exploring Csp2-O typeethers, very few reaction systems have been developed on the catalytic activation of Csp3-Oetheric bond for construction of Csp3-Csp3bond. However, there are several disadvantagesassociated with these methods include harsh reaction conditions and expensive reagents. Baseon our earlier performace, we have demonstrated a convenient and economical method forcross-coupling of benzyl/allyl ethers with allylsilane via iron-catalyzed etheric Csp3-O cleavage under mild conditions. The present protocol displays a desirable access to constructsp3-sp3C-C bonds together with introduction a C=C bond in high efficiency, and it can beapplied for selective reduction of benzylic or allylic ethers to their corresponding hydrocarboncompounds.