Total Syntheses of Hyperforin and Papuaforins A–C,and Formal Synthesis of Nemorosone through a Gold(I)‐Catalyzed Carbocyclization

The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane‐2,4,9‐trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A–C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)‐catalyzed 6‐endo‐dig carbocyclization of cyclic enol ethers for late‐stage functionalization.     

Total Syntheses of Hyperforin and Papuaforins A–C,and Formal Synthesis of Nemorosone through a Gold(I)‐Catalyzed Carbocyclization

The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane‐2,4,9‐trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A–C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)‐catalyzed 6‐endo‐dig carbocyclization of cyclic enol ethers for late‐stage functionalization.     

Solvolysis of 2-Bicyclo

The solvolysis rate of 2-bicyclo[3.2.2]nonyl p-toluenesulfonate (6-OTs) was nearly equal to that of cycloheptyl p-toluenesulfonate in 2,2,2-trifluoroethanol (TFE). This indicates that the ethylene bridge in 6-OTs does not significantly enhance the rate and that 6-OTs ionizes without anchimeric assistance. The solvolysis of [1-(13)C]-2-bicyclo[3.2.2]nonyl p-toluenesulfonate in methanol or TFE gave 2-substituted bicyclo[3.2.2]nonane, exo-2-substituted bicyclo[3.3.1]nonane, 2-bicyclo[3.2.2]nonene (10), and 2-bicyclo[3.3.1]nonene (11), whose distributions of (13)C labels were determined by quantitative (13)C NMR analysis using a relaxation reagent. The (13)C labels were exclusively placed at only two positions, the ratios of them were not unity, and the labels in 10 were less extensively scrambled than those in other products. These results indicate that the 2-bicyclo[3.2.2]nonyl cation is classical and that 10 is formed at a former ionization stage than 2-substituted bicyclo[3.2.2]nonane. The (13)C redistributions for both exo-2-substituted bicyclo[3.3.1]nonane and 11, which are yielded via 1,3-hydride shift, were similar to that of 2-substituted bicyclo[3.2.2]nonane, suggesting that 1,3-hydride shift occurs mainly at the solvent-separated ion pair.     

Synthesis and conformation of some 2,4-dioxa- and 2,4-dioxa-3-silabicyclo[3.3.1]nonanes

The conformation of the title compounds established by ¹³C and ¹H NMR spectroscopy shows that replacement of the 2- and 4-methylene groups in bicyclo[3.3.1]nonane by ether oxygen atoms strongly destablizes the cc conformation: in 2-oxabicyclo[3.3.1]-nonane the cc and the bc conformers are about equally populated, whereas in 2,4-dioxabicyclo[3.3.1]nonane the bc conformation predominates. The 2,4-dioxa-3-silabicyclo[3.3.1]nonanes also occur predominantly inthe bc conformation. As in the carbocyclic bicyclo[3.3.1]nonanes both wings are strongly flattened. A stereoselective synthesis of 3-methylbicyclo[3.3.1]nonane, an important model compound in this study, is described.     

The chemistry of the polycyclic polyprenylated acylphloroglucinols

With their fascinating biological profiles and stunningly complex molecular architectures, the polycyclic polyprenylated acylphloroglucinols (PPAPs) have long provided a fertile playing field for synthetic organic chemists. In particular, the recent advent of innovative synthetic methods and strategies together with C-C bond-forming reactions and asymmetric catalysis have revitalized this field tremendously. Consequently, PPAP targets which once seemed beyond reach have now been synthesized. This Review aims to highlight the recent achievements in the total synthesis of PPAPs, as well as notable methods developed for the construction of the bicyclo[3.3.1] core of these chemically and biologically intriguing molecules.     

Mass spectra of some mono- and disubstituted bicyclo [3.3.1]nonane dervatives

Conclusions It was shown that an analogy exists in the decomposition under electron impact of a series of mono- and disubstituted bicyclo[3.3.1]nonane derivatives and the corresponding adamantane derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 711–715, March, 1977.     

13C NMR spectroscopy of some 3- and 7-substituted bicyclo[3.3.1]nonanes

The ¹³C NMR spectra of a series of 3,7-substituted bicyclo[3.3.1]nonane derivatives are examined. Taken into account substituent influences, the ¹³C chemical shifts appear to be diagnostic for the conformation of the bicyclo[3.3.1]nonane derivative.     

The "hockey sticks" effect revisited: the conformational and electronic properties of 3,7-dithia-1,5-diazabicyclo[3.3.1]nonane from the QTAIM perspective

The conformational effects in bicyclo[3.3.1]nonanes, while thoroughly studied, have not yet received the full theoretical explanation. R. F. W. Bader's quantum theory of atoms in molecules presents unique opportunities for studying the stereoelectronic interactions (SEI) and weak intramolecular bonding leading to these effects. Here, we report the study of 3,7-dithia-1,5-diazabicyclo[3.3.1]nonane by means of the topological analysis of the calculated (MP2(full)/6-311++G**) and experimental (X-ray derived) charge density to reveal the origins of the so-called "hockey sticks" effect observed in similar compounds. A new explanation of the relative stability of bicyclo[3.3.1]nonane conformers based on the analysis of the QTAIM atomic energies is given. The H···H and S···S interactions in bicyclo[3.3.1]nonane and its dithia derivatives are shown to be significant factors contributing to the differences in the relative stability of the conformers.     

Synthesis of indoles condensed with a bicyclo[3.3.1]nonane skeleton

Derivatives of mono- and bisindoles condensed with a bicyclo[3.3.1]nonane skeleton were synthesized from bicyclo[3.3.1]nonane-2,6-dione and 6-hydroxybicyclo[3.3.1]nonan-2-one by means of the Fischer reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 315–318, March, 1979.     

Enantioselective total synthesis of (-)-neovibsanin G and (-)-14-epi-neovibsanin G

The first total synthesis of vibsane-type diterpenoids neovibsanin G and 14-epi-neovibsanin G has been achieved. Key to this endeavour was a late stage EtAlCl(2) mediated skeletal rich cascade leading to the bicyclo[3.3.1]nonane core in one step.     

Lone pairs vs. covalent bonds: conformational effects in bicyclo[3.3.1]nonane derivatives

Structural Chemistry - Investigations on the relative energy of two least-strain conformers for bicyclo[3.3.1]nonane 1, bicyclo[3.3.1]nonan-9-one 2, and their heteroanalogues:...     

Electrophilic Additions to Strained Bridgehead Olefins. Estimation of Strain by Comparison with the Solvolysis of Bridgehead Bromides

The addition of water, acetic acid, and hydrogen bromide to the strained bridge-head olefins bicyclo[3.3.1]-1(2)-nonene (1) , bicyclo[4.2.1]-1(8)-nonene (2) , and bicyclo[4.2.1]-1(2)-nonene (3) gives exclusively the bridgehead alcohols, acetates, and bromides, respectively. The reaction rate constants for the addition of acetic acid to the bridgehead olefins 1,2 and 3 , and the solvolysis rates for the related 1-bromo-bicyclo[3.3.1]nonane (4) and 1-bromobicyclo[4.2.1]nonane (5) were measured. A comparison of the activation enthalpies of these two reactions gives an estimate of relative strain of the bridgehead double bond. The strain in the bicyclo[4.2.1]nonenes 2 and 3 is similar to that in trans-cyclooctene (8-9 kcal/mol).     

Alpha,alpha'-annulation of 2,6-prenyl-substituted cyclohexanone derivatives with malonyl chloride: application to a short synthesis of (+/-)-clusianone. Formation and rearrangement of a biogenetic-like intermediate

Conditions were found for the successful Effenberger alpha,alpha'-annulation of 3,3-dimethyl-2,4,6-triprenyl cyclohexanone silyl enol ethers with malonyl chloride to give the corresponding bicyclo[3.3.1]nonane-trione in 35% yield, this result allowing a short synthesis of (+/-)-clusianone. An isomeric rearranged bicyclo[3.3.1]nonane-trione was also isolated in 25% yield, and changing the Lewis acid resulted in formation of a lavandulyl-substituted phloroglucinol derivative in 38% yield. The mechanism of formation of these two last products mimics the biogenetic pathway to PPAPs. [reaction: see text].     

Synthetic studies on phloroglucins: a new approach to the bicyclo[3.3.1]nonane system via the regioselective ring-opening of the methoxycyclopropane

A new synthetic approach to the bicyclo[3.3.1]nonane system, a common structure in a number of polyisoprenylated phloroglucinol derivatives (phloroglucins), has been developed. The key step in our approach is a ‘one-pot’ procedure of two successive reactions, the intramolecular cyclopropanation reaction which affords the tricyclo[4.4.0.0^5,7]dec-2-ene derivative and its methoxy group directed regioselective ring-opening reaction mediated by ZnCl₂, producing the desired bicyclo[3.3.1]nonane as the sole product.     

Syntheses of bicyclic 1,2-diols via the ring-expansion of bridgehead aldehydes of bicyclo[3.2.1]octane and bicyclononanes with benzoyl triflate

Bridgehead aldehydes of bicyclo[3.2.] loctane (11a), bicycio-[3.3.1]nonane (12a), and bicyclo[3.2.2]nonane (13a) have been subjected toacylative ring-expansion by using benzoyl trifluoromethanesulfonate (trif-late) to give mixtures of two or three bicyclic 1,2-diol monobenzoates containing the hydroxyl group on the bridgehead carbon. Control experiments have shown that the reaction is kinetically controlled. The direction of the ring-expansion has been found to be predictable by comparing the strain energies calculated by molecular mechanics of the parent hydrocarbons corresponding to the produced diol monobenzoates. The major monobenzoates, easily isolated in practical yields by crystallization or column chromatography, have been converted to the corresponding diols, and their structures determined. For synthetic purposes, 11a gives bicyclo[3.3.1]nonane-1,endo-2-diol (27), and 12a the endo and exo isomers of bicyclo[4.3.1]decane-1,2-diol (33 and 35, respectively). From 13a is furnished bicyclo[4.2.2]decane-1,2-diol (42). Diols 27, 33. and 42 are conveniently oxidized to the corresponding ketols by using silver carbonate in 50 – 80% yields. The oxidation of diol 35 to 1-hydroxybicyclo[4.3.1]decan-2-one (34) failed under similar conditions, but it was achieved by the Corey oxidation by using dimethylsulfide -chlorine complex.     

A radical mediated approach to the core structure of huperzine A

The synthesis of the core structure of huperzine A by cyclisation of 2-pyridylmethyl radicals is described. (2-Methylpyridin-3-yl)cyclohexenols are directly selenated at the benzylic position by deprotonation/selenation and the products undergo either 5-exo-trig or 6-exo-trig radical cyclisations giving access to hexahydroindenopyridines and the bicyclo[3.3.1]nonane core of huperzine A, respectively.     

Towards an enantiospecific total synthesis of garsubellin A and related phloroglucin natural products: the α-pinene approach

The first enantiospecific approach to garsubellin A and related phloroglucin natural product nemorosone, of contemporary interest from (−)-α-pinene, has been delineated. Through a series of stereospecific operations, the requisite stereochemistry of the prenyl groups has been secured. Kende cyclization has been employed as the key step to construct the functionalized bicyclo[3.3.1]nonane core.     

Conformational studies by dynamic NMR. 93.(1) Stereomutation,enantioseparation, and absolute configuration of the atropisomers of diarylbicyclononanes

The structure of 9-(4-methoxyphenyl)-9-(3-methylphenyl) bicyclo[3.3.1]nonane (1) has been determined by single-crystal X-ray diffraction, and the rotation barriers about the two aryl-C9 bonds have been measured by variable temperature NMR spectroscopy in solution. In the case of 9-(4-methoxyphenyl)-9-(1-naphthyl)bicyclo[3.3.1]nonane (3), the barrier involving the naphthyl-C9 rotation was found to be so high as to allow the physical separation of the two atropisomers by enantioselective HPLC at ambient temperature: the absolute configuration could be established on the basis of the corresponding CD spectra. It was also observed that the Ar-C9 rotation barriers of monoaryl-substituted nonanes are much lower than those of the corresponding diaryl-substituted nonanes.     

Reaction of α,β-unsaturated trifluoromethyl ketones with cyclic enamines

The reactions of ,-unsaturated trifluoromethyl ketones containing aromatic and heteroaromatic substituents with 1-morpholinocyclopentene, 1-morpholinocyclohexene, and 1-methyl-4-morpholino-1,2,5,6-tetrahydropyridine were studied. The reactions proceeded stereospecifically to give the corresponding bicyclo[3.2.1]octane, bicyclo[3.3.1]nonane, and azabicyclo[3.3.1]nonane derivatives.     

Progress toward the Synthesis of garsubellin A and related phloroglucins: the direct diastereoselective synthesis of the bicyclo[3.3.1]nonane core

[reaction: see text] A highly diastereoselective single-step cyclization reaction provides access to the bicyclo[3.3.1]nonane core of the polyprenylated phloroglucin natural product garsubellin A. Further elaboration to a more functionalized analogue involves a sequential Claisen rearrangement/Grubbs olefin cross-metathesis strategy. Additionally, this strategy was extended to the preparation of the bis-quaternary carbon array found at the bridgehead positions of the phloroglucin natural products.