Abstract
This thesis, which is divided into two parts, aims on the studies of masked ortho-benzoquinones (MOBs) and their applications. In the first part the chemistry of syn-1,5-diene compounds such as 143 and 180 which underwent the tandem oxy-Cope / ene reactions in sealed tubes is discussed. In the second part the chemistry of anti-1,5-diene compounds such as 209 and 220 which, under similar reaction conditions, underwent a one-carbon expansion through [1,2]-rearrangement process is discussed.PartⅠ: Oxidation of 5-Bromo-2-methoxyphenol (146) with (diacetoxy) iodobenzene (DAIB) followed by intramolecular Diels-Alder reaction with trans-crotyl alcohol afforded the tricyclic ketone 145 which underwent the Stille coupling and nucleophilic addition reactions to generate the syn-addition product 151. The tricyclic triene 151 was subjected to Diels-Alder reaction with symmetrical dienophiles, such as maleic anhydride and N-phenylmaleimide, to generate single DA adducts, 143 and 153, respectively. syn-1,5-Dienes 143 and 153 in sealed tubes underwent the tandem oxy-Cope/ene reaction furnishing multicyclic compounds 155 and 156. Compound 151 when subjected to Diels- Alder reaction with methyl vinyl ketone (MVK) afforded the DA adducts 180 and 181 with stereoisomeric ratio of 1:1. During the sealed tube reaction, compound 180 underwent the tandem oxy-Cope/ene reaction generating multicyclic compound 182; however, compound 181 was unreactive under similar reaction condition. Under basic reaction condition, the tricyclic diene 180 underwent the anionic oxy-Cope rearrangement / aldol condensation reactions to afford the product 184; the carbonyl-protected tricyclic diene 185 furnished compound 186 during anionic oxy-Cope rearrangement. Structure 186 is similar to the core structure of the natural product, vinigrol (65). Cleavage of the C–C double bond by ozonolysis in multicyclic compounds 155 and 156 furnished the (cis,cis-fused)-5,6,5- tricyclic systems 189 and 190, respectively, whereas their oxidative cleavage with Pb(OAc)4 afforded (cis,trans-fused)-5,6,6-tricyclic systems 192 and 193, respectively. The stereochemical centers of 192 and 193 are the same as the chiral centers found in natural product, (+)-elisabethin A (194).Part II: trans-2-Ethoxy-5-(1-propenyl)phenol (200) was oxidized with DAIB and subjected to intramolecular Diels-Alder reaction to afford the tricyclic compound 201. Nucleophilic addition reaction of 201 with cerium reagent followed by Diels-Alder reaction with symmetrical dienophiles, such as maleic anhydride and N-phenylmaleimide, afforded the DA adducts 209 and 210, respectively. Under similar reaction conditions described in Part I, compound 210 in the sealed tube underwent the one-carbon expansion to furnish tricyclic ketone 211 and the tricyclic lactone 212. However, if the sealed tube was pre-washed with saturated NaOH, only compound 211 was observed. Diels-Alder reaction of compound 152 with MVK furnished the DA adducts 220 and 221 with stereoisomeric ratio of 1:1. The 1,5-diene 220 in sealed tube afforded the rearrangement products 222, 223 and 224. Tricyclic diene 221 was insensitive to one-carbon expansion reaction; the starting material 221 was recovered. Compound 220 in sealed tube pre-washed with saturated NaOH furnished the rearrangement products 222 and 223. Plausible mechanisms for the rearrangement of anti-1,5-dienes in a sealed tube pre-washed with saturated NaOH are described as follows. In the case of lactone 224, the mechanism for the formation of this product is similar to pinacol-pinacolone rearrangement.