Tandem Oxidative Acetalization−Intramolecular Diels−Alder Reactions of 2-Methoxyphenols. Simple Synthesis of Bicyclo[2.2.2]octenone Derivatives

Abstract

Intramolecular Diels-Alder reactions of in situ generated masked o-benzoquinones are described. Oxidation of methyl vanillate (2) in the presence of allyl alcohol (1a), trans-crotyl alcohol (1b), cinnamyl alcohol (1c), and homoallyl alcohol (1d) resulted in the formation of masked obenzoquinones 8a-d that underwent intramolecular Diels-Alder reactions under reaction conditions to furnish adducts 14a-d in 53-75% yields. This tandem oxidative acetalizationintramolecular Diels-Alder process was extended to other 2-methoxyphenols such as 2-methoxy-4-methylphenol (3), guaicol (4), methyl isovanillate (5), methyl syringate (6), and 2,6-dimethoxy-4-methylphenol ( 7) to obtain adducts 15a-d, 16a-c, 17a-d, 18a-d, and 19a-d, respectively. While intramolecular Diels-Alder reactions of the masked o-benzoquinones 10a, 12d, and 13d were found to be less efficient, the masked o-benzoquinones 9a-d, 10b, 10c, 11a-d, 12a-c, and 13a-c furnished the desired products in 38-80% yields. Masked o-benzoquinones 21a-d generated from 2 and substituted acrylic acids 20a-d underwent intramolecular Diels-Alder reactions to provide the tricyclic lactones 22a-d in 32-40% yields.

Pd-Catalyzed Cascade Reactions of Aziridines: One-Step Access to Complex Tetracyclic Amines

“…The resulting N-allylated product 12 then undergoes cycloaddition to form product 6 , the rate of which is controlled by the aziridine and allyl substituents. Although a Pd-catalyzed elimination/intermolecular DA process has been reported previously, to the best of our knowledge, this is the first example of a sequential Tsuji–Trost/IMDA cascade. , …”

“…Although a Pd-catalyzed elimination/intermolecular DA process has been reported previously, 17 to the best of our knowledge, this is the first example of a sequential Tsuji–Trost/IMDA cascade. 18 , 19 …”

Incorporation of catechyl monomers into lignins: lignification from the non-phenolic endviaDiels–Alder cycloaddition?

“…Confirmation was from reported 1 H NMR data of a compound that has the common oxatricyclo structure. 50 In the COSY spectrum (Fig. 4A), proton 2′ correlated with protons α and 6′, but not with the β proton.…”

Application of Carbohydrate-Templated Asymmetric Diels–Alder Reaction to the Syntheses of ent-Penicillones A and B

“…With phenol 8 in hand, the next step was the asymmetric intramolecular Diels–Alder reaction of the masked o -benzoquinone, which was generated from phenol 8 and diacetoxy­iodo­benzene (DAIB) in the presence of trans -crotyl alcohol (Table ). The reaction was first carried out at −30 °C for 6 h to form MOB 9 before the reaction mixture was heated under reflux for 20 h. The intramolecular Diels–Alder reaction of 9 proceeded smoothly at reflux to generate desired tricyclic β,γ-enones 10 and 11 in 58% total yield and a 2:1 ratio (entry 1). Compounds 10 and 11 were easily separated by silica-gel chromatography.…”