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A stereoselective approach to tricyclic core of yaoshanenolides from simple aromatic precursor is described. Cycloaddition of highly reactive spiroepoxycyclohexa-2,4-dienone, stereoselective Grignard reaction, alkylation, and ring-closing metathesis reaction are the key features of our approach.

The efficient generation of complex molecular architectures from simple precursors is one of the most important aspects in the design and development of synthetic methodologies. The chemistry of reactive species generated by the oxidative dearomatization of phenols, such as o -quinone acetals, 6-acetoxycyclohexa-2,4-di­enones, and their congeners, has stimulated widespread interest among organic chemists, and the use of such reactive species has emerged as a powerful method for the efficient synthesis of complex molecules. Our approach to create molecular complexity and diversity involves the oxidative dearomatization of 2-(hydroxymethyl)phenols to give spiro[cyclohexa-2,4-dienone-6,2′-oxiranes], followed by cycloaddition and transformation of the resulting adducts in the ground and excited states. In this account, we describe the evolution of the methodology and its application which has led to the development of novel and efficient routes to a diverse array of complex molecular architectures from simple aromatics. 1 Introduction 2 Cycloaddition of Cyclohexa-2,4-dienones of Types 3 and 4 and Manipulation of the Adducts in the Ground and Excited States 2.1 Cycloaddition of Cyclohexa-2,4-dienones of Types 3 and 4 : An Efficient Route to Functionalized and Appended Bicyclo[2.2.2]octanes 2.1.1 Cycloaddition of Cyclohexa-2,4-dienones of Types 3 and 4 with Electron-Deficient π-Partners 2.1.2 Cycloaddition of Cyclohexadienones of Type 4 with Vinyl Ethers and Vinyl Acetate 2.1.3 Cycloaddition of Cyclohexadienones of Types 3 and 4 with Acyclic 1,3-Dienes: Direct Entry to Bicyclo[2.2.2]octenones Having an endo -Vinyl Group 2.2 Manipulation of the Oxirane Moiety or the Chloromethyl and Hydroxy Groups in the Adducts: Synthesis of Embellished Bicyclo[2.2.2]octanes 2.3 3,3-Sigmatropic Shift in Bicyclo[2.2.2]octanes: A General Stereoselective Route to Functionalized cis -Decalin Derivatives 2.4 Sigmatropic Rearrangements of β,γ-Enones in Excited States: Stereoselective Routes to Bicyclo[3.3.0]- and Bi­cyclo[4.2.0]octanes and Tricyclic Compounds 3 Synthetic Applications 3.1 Synthesis of Hirsutic Acid C and the Framework of ­Pupukeananes from a Common Precursor 3.2 Chemistry of Fused Spiro[cyclohexa-2,4-dienone-6,2′-oxiranes] and Their Adducts: Synthesis of Propellanes and ­Steroid–Polyquinane Hybrids 3.2.1 A General Route to [3.3.3]- and [4.3.3]Propellanes 3.2.2 Synthesis of Steroid–Polyquinane Hybrids 3.3 Synthesis of Tri- and Tetracyclic Networks of Atisane Diterpenoids 3.3.1 Synthesis of Tricyclo[6.2.2.0 1,6 ]dodecanes and Their Homologues 3.3.2 Synthesis of the Tetracyclic Network of Atisane Diterpenoids: An Interesting Manifestation of Subtle Control by a Remote Functional Group 3.4 Intramolecular Cycloaddition of Cyclohexa-2,4-dienones: Synthesis of Platencin 4 Summary and Outlook

Oxidation of the hydroxymethylphenol (I) generates a dearomatized 6,6-spiroepoxycyclohexa-2,4-dienone intermediate which is trapped by Diels—Alder reaction with acrylates.

Unlike other oxidizing agents such as MnO2, PCC, or Dess—Martin periodinane, IBX oxidizes 2-furylcarbinols smoothly and without rearrangement-derived side products.

A novel and efficient synthesis of tricyclopentanoids via inverse demand π4s+π2s cycloaddition and photochemical reaction of annulated[2.2.2]octenones having an α-alkoxy-β,γ-unsaturated carbonyl chromophore, is described.

An attempt towards synthesis of homohypostrophene derivative, 1,2,6,8-tetrachloro-7,7-dimethoxytetracyclo[6.3.0.02,6.05,9]undeca-3,10-diene from 2,3,5,6-tetrachloro-4,4-dimethoxypentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione is described.

A highly periselective cycloaddition of cyloheptatriene and cyclohexa-2,4-dienones( 2a-c ) to endo tricyclic systems ( 6a-c ) and their photo conversion to cage compunds ( 7a-c ) has been reported. It has been shown that the adduct 6c arise via Cope rearrangement of the initially formed π 4s (dienone) + π 2s (CHT) adduct 5c .

A novel, photodecarbonylation upon singlet excitation of β,γ-enones having wider synthetic potential is described.

A novel and general approach for the synthesis of linearly fused cis:anti:cis tricyclopentanoids and protoilludane framework having fused four, six and five membered rings from common precursors has been delineated. Photochemical sigmatropic 1,2-acyl shift (or oxadi-π-methane rearrangement) and 1,3-acyl shift in annulated bicyclo[2.2.2]octenones are the key features of this approach. An efficient one step synthesis of epoxy ketones 15–17 via π 4 s+ π 2 s cycloaddition of in situ generated cyclohexa-2,4-dienone 11 has been reported. Further transformation of 15–17 and their congeners to a variety of chromophoric systems 22–31 has been described. The structure and stereochemistry of annulated bicyclo[2.2.2]octenones 15–31 has been established through their high field 1 H-NMR (300MHz), 13 C-NMR, decoupling experiments and cosy spectra. Photochemical behaviour of selected chromophoric systems upon triplet ( 3 T) and singlet ( 1 S) excitations has been investigated. While triplet excitation ( 3 T) of 23, 24, 26–28, 30–32 and 35 led to formation of tetracyclic systems 38–47 , the singlet excitation ( 1 S) of 23, 24, 27, 28, 29b, 31b, 36 and 55 furnished the protoilludanoids 56–63 . Interestingly, 29b did not undergo 1,2-acyl shift upon triplet excitation, but it underwent 1,3-acyl shift upon singlet excitation to give 60 . Cleavage of cyclopropane ring in some of the tetracyclic products has also been investigated. Reductive cleavage of 38, 44, 46 and 47 to tricyclic systems 50–53 has also been reported.

Synthesis of 1-hydroxy[5.3.1.02,6]undecadienones 15–18 from annulated bicyclo[2.2.2]octenones 10–14 via carbocationic rearrangement has been described and a new route to cis:syn:cis tricyclopentanoids 25, 26 from 15, 18 reported.

Synthesis of angularly and linearly fused tetraquinanes 13 and 15 via triplet sensitized photoreaction of appropriately appended tricyclo[5.2.2.02,6]undecane systems such as 10a and 10d, followed by aldol condensation, is reported. In addition, synthesis of tricyclic systems 10a, d from readily available aromatic precursors such as 8a, b has also been described.

In the absence of a reactive alkene, the Diels-Alder dimer of 2,6-dimethyl-6-hydroxycyclohexa-2,4-dienone rearranges at 160 °C to a new dimer via a reverse Diels-Alder reaction, two α-hydroxyketone rearrangements, two Micheal additions, and two aldol condensations. © 1997 Elsevier Science Ltd.

A novel, efficient and stereospecific synthesis of (±) capnellene from p-cresol is reported.

A novel, general, and stereoselective route for rapid creation of functionalized, linearly fused cis:anti:cis triquinanes from aromatic precursors has been presented. Cycloaddition of 2-methoxyspiro[cyclohexa-2,4-diene-6-2‘-oxacyclopropan]one with various dienophiles and the photochemical reaction of appropriately designed tricyclic systems, having an α-methoxy β,γ-enone chromophore upon triplet (3T) sensitization, are the key elements of our approach. A new and efficient methodology for the synthesis of endo-annulated bicyclo[2.2.2]octenones having an α-methoxy β,γ-enone chromophore (23−36) from o-vanillyl alcohol has been reported. The 2-methoxyspiro[cyclohexa-2,4-diene-6-2‘-oxacyclopropan]one was generated by oxidation of o-vanillyl alcohol and trapped with cyclopentadiene (17), spiroheptadiene (18), and dimethylfulvene (19) to give the adducts 20−22, which were elaborated to a variety of chromophoric systems 23−36. The structure and stereochemistry of the tricyclic chromophoric systems (20−36) has bee...

A novel and general approach to the synthesis of functionalised protoilludane skeletons having fusedfour-, six- and five-membered rings is described. A photochemical sigmatropic 1,3-acyl shift in endo-tricyclo[5.2.2.02,6]undecanes having a β,γ-unsaturated carbonyl chromophore, and π4s + π2s cycloaddition of spiro[cyclohexa-2,4-diene-oxiran]-6-one are the key features of this approach. An efficient one-step synthesis of the epoxy ketone 11 by π4s + π2s cycloaddition of the in situ generated spiro[cyclohexa-2,4-diene-oxiran]one is reported. Further transformation of 11 to a variety of endo-tricyclo[5.2.2.02,6]undecanes (20, 25, 28, 30 and 31) and their photochemical behaviour upon singlet (1S) excitation is described. Direct excitation of all the tricyclic chromophoric systems in benzene neatly furnished the protoilludanoids 32–36.

Synthesis of a highly functionalised triquinane 4 from 2-hydroxy-3-methoxy-6-methylbenzyl alcohol is reported.

A novel, stereoselective synthesis of sterpuranes and coriolin via modulation of the photochemical reactivity of a tricyclic system having a β,γ-enone chromophore, which was assembled via intramolecular π4s + π2s cycloaddition of 1-oxaspiro[2.5]octa-5,7-dien-4-ones, is presented.

Synthesis of bicyclo[2.2.2]octenones 4a–d, 9 and their Cope rearrangement to substituted cis-decalins 3a–d, 12, is described.

A novel, general, and efficient method has been developed for the synthesis of highly functionalized spiro δ-lactones from aromatic precursors. Our methodology involves a tandem oxidative dearomatization-rearrangement of tertiary furyl carbinols and ring-closing metathesis as key features. This method allows an access to the spirolactones attached to carbocycles of various sizes.

Cycloaddition of 6-hydroxy-2,6-dimcthylcyclohexa-2,4-dienones with ethyl vinyl ether, butyl vinyl ether, vinyl acetate and vinyl phenyl sulphone leading to a stereoselective entry into bicyclo[2.2.2]octanes having quaternary methyl group is reported. A novel thermal 1,2-methyl migration has also been described.

Cycloaddition of electron-deficient cyclohexa-2,4-dienones with nitroolefins leading to functionalized bicyclo[2.2.2]octenones with nitro groups is reported. A highly unusual regioselectivity was observed. Crystal structure of one of adducts has also been reported.

A stereoselective route towards protoilludanoids from simple aromatic precursor is described. The methodology involves in situ generation of spiroepoxycyclohexadienone and cycloaddition with cyclopentadiene and photochemical 1,3-acyl shift., © Elsevier

A new and efficient synthesis of a variety of highly embellished bicyclooctenones having an endo-vinyl moiety and their sigmatropic shifts in ground and excited states leading to a stereoselective ...

Synthesis of the tricyclic keto-epoxides 2 and 3 from the readily available aromatic precursors 4,5 respectively, via generation and interception of spiroepoxycyclohexa-2,4-dienones is described.

Formal syntheses of coriolin 1, a triquinane metabolite isolated from Coriolus consors, are described. Oxidation of 6-methyl saligenin 2 in the presence of cyclopentadiene gave the tricyclic keto epoxide 4 which was elaborated to tricyclo[5.2.2.02,6]undecenones 5 and 18 containing the major structural and stereochemical features of coriolin, in latent form. Triplet sensitized 1,2-acyl shifts in 5 and 18 gave tetracyclic compounds 6 and 19 in a stereoselective manner. Reductive cleavage of cyclopropane rings in 6 and 19 with H2/Pd-C and TBTH-AIBN respectively, furnished the functionalised triquinanes 7 and 20b which are known precursors for coriolin.

An efficient synthesis of the title compound by Diels-Alder cycloaddition of spiro (4.4) nonadiene with p-benzoquinone followed by photochemical ring closure is described.

A simple one step synthesis of tricyclo (2.2.2.02,6) tetradecadienones and 5-spiro tricyclo (2.2.2.02,6) undecadienone by trapping of 2,4-cyclohexa-dienone with various dienophiles followed by photochemical oxa-di-π-methane rearrangement of the resulting adducts to polyquinanes is described.

A simple synthesis of spirodiones (2)&(3) via n6s+ n2s photocyclization of the Deils-Alder adducts (4)&(5) obtained by reactions of spiro (4,2) heptadiene (6) and spiro (4,4) nonadiene (7) with 1,4- naphtho-quinone in homogeneous and micellar media. A remarkable catalytic effect by micelle on cycloaddition is noted.

A short synthesis of various tricyclo(5.2.2.02 6) undecadienones by Diels-Alder reaction of a 2,4-cyclohexadienone with dienes and their oxa-di π- rearrangement is reported.