Study On Novel Sigmatropic Rearrangements And Their Application In The Development Of Potential Aroma Compounds

Sigmatropic rearrangement is an important reaction in organic chemistry. Because of its special stereoselectivity and regioselectivity, realization of molecule's structure reorganization and carbon-carbon bond's formation, establishing compound's particular framework instead of some conventional reaction, it has been widely used in the synthesis of a diverse range of natural products and other targets. Several research of theoretics and application about sigmatropic rearrangement have been reported. Again, tandem reaction of sigmatropic rearrangement and other reaction has also begun to become research focus because of it's high-efficiency and concision, meeting the orientation of modern organic chemistry.Sigmatropic rearrangement studied in this thesis mainly includes Ireland-Claisen rearrangement and [2,3]-Wittig rearrangement.In part 1 of this thesis, we investigated Ireland-Claisen rearrangement of allyl esters of unsaturated acids systemically, and applied the rearranged products for derivation to some fragrant molecules; Four topics are addressed, which are:1. We studied Ireland-Claisen rearrangement of allylic acrylates. Combined Baylis-Hillman reaction condition with Ireland-Claisen rearrangement, we have established a novel DABCO-catalyzed Ireland-Claisen rearrangement of allylic acrylates. Furthermore, in the course of studying the scope and limitations, we empolyed readily available molecules 7a-o as the starting materials. The rearranged products represents new unsaturated compounds 19a-m after rearrangement.2. We studied DBU-mediated Ireland-Claisen rearrangement. Using DBU as the base for enolization of allylic esters of unsaturated acids 9-16, we found a novel DBU-mediated tandem Ireland-Claisen rearrangement /isomerization reactions and established a consecutive Ireland-Claisen rearrangement /Cope rearrangement. By investigation of its scope and limitations, we found the protocol could work well for a wide variety of substrates to provide polyfunctionalized conjugated carboxylic acids 23a-f, 25, 29a-f, 31a-c, 33 and 35a-g .3. We studied Ireland-Claisen rearrangement of propargylic esters of unsaturated acids. First, when operating the DABCO-catalyzed Ireland-Claisen rearrangement of propargylic acrylates 18b-d, we added dienophiles 40a-f in the reaction system to capture the rearranged allenes products respectively. The Diels-Alder adducts 41a-i were obtained with complete regioselectivity. Thus a novel tandem Ireland-Claisen rearrangement /Diels-Alder reaction process with propargylic acrylates has been developed. Second, using DBU as the base for enolization of propargylic esters of unsaturated acids 18e-k, we developed a tandem Ireland-Claisen rearrangement /isomerization reactions. It has been shown that the reaction sequence affords triene molecules 42a-b and 43a-b in moderated to high yields. Interestingly, with allyl hexa-3,5-dienoates 18i-j as the substrate, the rearranged products underwent further aromatization to give uniquely substituted benzyl acids 44a-b. This offers an efficient synthetic way to this kind of aromatic acids.4. Based on the concepts of fragrance chemistry, under the guidance of molecules' structure and odour relationships, we synthesized a list of potential odorants 46a-s, 47a-b, 48a-d and 49a-e by esterification, lactonization and reduction of the Ireland-Claisen rearranged products. Some of them were evaluated. It indicated that these deviratives prossess fruity and floral flavour.In part 2 of this thesis, we attempted to investigate the synthesis of quarternary carbon alcohols using [2,3]-Wittig rearrangement. By exploring [2,3]-Wittig reaction condition of some substrates, we found that [2,3]-Wittig rearrangement could be applied only to non-substituted allyl ethers 52 a and 56a. However, for substituted substrates 52b and 56b, negative results were obtained. Thus, more detailed work has to be done to demonstrate the scope and limitations.