Cycloaddition of Spiroepoxycyclohexa-2,4-dienones, Radical Cyclization and 1,3-Acyl Shift in Excited State: Aromatics to Sterpuren-4-one.

A stereoselective route to sterpuren-4-one from a simple aromatic precursor is presented. Oxidative dearomatization, π4s + π2s cycloaddition of 6,6-spiroepoxycyclohexa-2,4-dienones with ethyl acrylate, radical cyclization and 1,3-acyl shift in excited state are the important aspects of our approach. An interesting effect of a remote substituent on radical cyclization has also been presented.

π(4)s + π(2)s Cycloaddition of Spiroepoxycyclohexa-2,4-dienone, Radical Cyclization, and Oxidation-Aldol-Oxidation Cascade: Synthesis of BCDE Ring of Atropurpuran.

Synthesis of a tetracyclic ring system (BCDE) of atropurpuran is described. Oxidative dearomatization, cycloaddition of spiroepoxycyclohexa-2,4-dienone, radical cyclization, and a tandem oxidation-aldol-oxidation are the key features of our methodology.

Intramolecular cycloaddition in 6,6-spiroepoxycyclohexa-2,4-dienone: simple aromatics to (+/-)-platencin.

A formal total synthesis of platencin from a simple aromatic precursor is described. Transformation of the aromatic compound into reactive spiroepoxycyclohexa-2,4-dienone and intramolecular cycloaddition are the key features of our methodology. 2-Hydroxymethyl-6-(3-hydroxy-hex-5-enyl)-phenol was oxidized with NaIO(4) to give a dimer that, upon a retro-Diels-Alder reaction, generated the spiroepoxycyclohexa-2,4-dienone that underwent intramolecular Diels-Alder reaction to give a tricyclic adduct having a core structure of platencin and appropriately disposed functional groups in a single step. Reduction of the double bond present in the ethano-bridge, manipulation of the oxirane ring and introduction of a double bond in the six-membered ring furnished a tricyclic intermediate which has already been converted into platencin.

Diels-Alder cycloaddition and ring-closing metathesis: a versatile, stereoselective, and general route to embellished bridged bicyclic systems, carbocyclic framework of secoatisanes, and homologues.

A general and stereoselective methodology for the synthesis of bridged bicyclic octenones having various types of alkenyl chains and a tricyclic framework of secoatisanes and higher analogues is reported. In situ generation and cycloaddition of 2-allyl-6,6-spiroepoxycyclohexadienones with ethyl acrylate gave bicyclo[2.2.2]octanes having an allyl group at the bridgehead and other chemically distinguishable functionality in a regio- and stereoselective fashion. Selective manipulation of adducts led to the introduction of other olefinic chain of variable lengths at the carbon adjacent to the bridge head. Ring-closing metathesis in bicyclooctanes having olefin tethers provided an efficient route to tricyclic systems having bicyclo[2.2.2]octane framework having spiro-fused six-, seven-, and eight-membered rings.

Molecular complexity from aromatics: a novel, stereoselective route to tricyclo[5.2.2.0(1,5)]undecenones, tricyclo[6.2.2.0(1,6)]dodecenones, and [n.3.3]propellanes.

A general stereoselective route to functionalized and substituted tricyclo [5.2.2.0(1,5)]undecenones, tricyclo[6.2.2.0(1,6)]dodecenones, and [3.3.3]- and [4.3.3]propellanes from simple aromatic precursors is reported. The methodology involves generation and cycloaddition of annulated cyclohexa-2,4-dienones with various acrylates followed by manipulation of the resulting tricyclic adducts, leading to functionalized tricyclo[5.2.2.0(1,5)]undecenones and tricyclo[6.2.2.0(1,6)]dodecenones endowed with a beta,gamma-enone chromophore. Photochemical reaction of the tricyclic chromophoric systems followed by reductive cleavage provided an efficient entry into propellanes.

Cycloaddition of cyclohexa-2,4-dienones, ring-closing metathesis, and photochemical reactions: a common stereoselective approach to duprezianane, polyquinane and sterpurane frameworks.

A novel approach to three different types of carbocyclic frameworks belonging to dupreziananes, sterpuranes, and polyquinanes from simple aromatic precursors has been presented. Cycloaddition of appropriately appended cyclohexa-2,4-dienones with acyclic dienes gave bridged bicyclic octanes suitably disposed with olefinic chains, which upon ring-closing metathesis led to functionalized tricyclo[5.2.2.0(1,5)]undecanes related to dupreziananes. Photochemical sigmatropic 1,2- and 1,3-acyl shifts in tricyclo[5.2.2.0(1,5)] undecanes upon triplet and singlet excitation provided stereoselective routes to sterpurane and polyquinane frameworks.

Cycloaddition between electron-deficient pi-systems, photochemical and radical-induced reactions: a novel, general, and stereoselective route to polyfunctionalized bridged bicyclo[2.2.2]octanes, bicyclo[3.3.0]octanes, bicyclo[4.2.0]octanes, and tricyclo[4.3.1.0(3,7)]decanes.

A novel, general, and stereoselective route to functionalized bridged bicyclo[2.2.2]octanes, bicyclo[3.3.0]octanes, bicyclo[4.2.0]octanes, and tricyclo[4.3.1.0(3,7)]decanes has been described. Various functionalized and substituted bicyclo[2.2.2]octanes endowed with a beta,gamma-enone chromophore were synthesized via cycloaddition of in situ generated cyclohexa-2,4-dienones with electron-deficient 2pi partners and manipulation of the resulting adducts. Triplet sensitized irradiation of bridged bicyclooctenones led to synthesis of bicyclo[3.3.0]octanoids, whereas the direct irradiation furnished bicyclo[4.2.0]octanes in stereoselective fashion as a result of modulation of reactivity in excited states. Further, manipulation of the adducts led to appropriately appended and functionalized bicyclo[2.2.2]octanes that upon radical induced cyclization provided an efficient and stereoselective route to the tricyclo[4.3.1.0(3,7)]decane (isotwistane) framework of pupukeananes.

Molecular complexity from aromatics: synthesis and photoreaction of endo-tricyclo[5.2.2.0(2,6)]undecane--a stereoselective route to tricyclic framework of protoilludanes.

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.

A novel and efficient synthesis of bicyclo[2.2.2]octenones and sigmatropic shifts in ground and excited states: stereoselective route to cis-decalins and diquinane frameworks.

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 route to substituted cis-decalins and diquinane frameworks have been described. Functionalized bicyclo[2.2.2]octenones having an endo-vinyl group and a beta,gamma-enone chromophore were prepared by in situ generation of 6-chloromethyl-6-hydroxycyclohexadienones and cycloaddition with butadiene (also generated in situ) followed by manipulation of the adducts. The presence of contiguous carbonyl, hydroxyl, and chloromethyl groups in adducts led to the introduction of various alkyl groups alpha to the ketone in a stereoselective fashion. The 3,3-sigmatropic shift in the bridged bicyclic compounds gave the corresponding cis-decalins, whereas the triplet sensitized irradiation led to the formation of diquinanes as a result of a 1,2-acyl shift.

Efficient stereoselective synthesis of novel steroid-polyquinane hybrids.

A synthesis of steroid-polyquinane hybrids, a new class of molecular entities, is described. [reaction: see text]

Hybrid systems through natural product leads: an approach towards new molecular entities.

Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain integration of key structural/functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.

Cycloaddition of cyclohexa-2,4-dienones with electron deficient 2 pi partners: a novel and stereoselective route to functionalized bicyclo[2.2.2]octenones.

A novel route to functionalised bicyclo[2.2.2]octenones via pi 4s + pi 2s cycloaddition of cyclohexa-2,4-dienones with electron deficient 2 pi partners, and crystal structure of 1,7-dimethyl-5-hydroxy-5-chloromethyl-2-carboethoxy bicyclo[2.2.2]oct-7-ene-6-one, is reported.