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Thesis (Ph. D.)--Ohio State University, 2002. / Title from first page of PDF file. Document formatted into pages; contains xiv, 242 p.). Includes abstract and vita. Advisor: Leo A. Paquette, Dept. of Chemistry. Includes bibliographical references (p. 233-242).

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As part of a continuing study of the synthesis and chemistry of new, substituted pentacyclo(5.4.0.0²，⁶.0³，¹º.0⁵，⁹)undecanes, the following compounds have been synthesized: 1: X=O, Y=SiMe_3; 2: X=CH_2, Y=SiMe_3; 3: X=O, Y=Cl; 6: X=OAc, Y=H; 8: X=OC(O)Ph, Y=H; 9: X=OSO_2Ph, Y=H; 11: X=OH, Y=H; 12: X=OMe, Y=H; 14: X=CHSiMe_3, Y=SiMe_3; 15: X=OH, Y=Cl; 16: X=OAc, Y=Cl; 17: X=OMe, Y=Cl. An important objective of this work is to prepare new polycyclic cage compounds which can be utilized as intermediates for the synthesis of new, substituted tricyclopentanoid natural products (triquinanes) and related systems. Compounds 1-4 were identified as target molecules in this connection.

Employing a chiral pool strategy, enantiospecific syntheses of di- and triquinanes have been accomplished. α-Campholenaldehyde 95, readily available from the abundantly available monoterpene α-pinene 94, has been utilised as the chiral starting material. To begin with, enantiospecific synthesis of the diquinane 134 has been developed employing Nazarov cyclisation of the cross-conjugated dienone 132 as the key reaction (Scheme 37).71 Synthesis of the dienone 132 was accomplished by selenium dioxide mediated oxidation of the olefinic methyl group in α-campholenyl methyl ether 130, followed by further elaboration of the resultant aldehyde 131. OMe P2O5 MsOH The Nazarov cyclisation strategy has been further extended, as depicted in Scheme 38, for the synthesis of the triquinane enones 145 and 146 via the cross conjugated enone 144.71 The dienone 144 was obtained from the diquinane 136, which is readily available from campholenaldehyde 95 via an intramolecular rhodium carbenoid CH insertion reaction. Of the three methyl groups in campholenaldehyde 95, the olefinic methyl group can easily be functionalised, for example, via allylic oxidation. However, the remaining two tertiary methyl groups are difficult to functionalise, and there is no report in the literature on the utility of these two gem dimethyl groups either for functionalisation or for further elaboration, and remained only as gem dimethyl group in the products. It was conceived that it could be possible to utilise the tertiary methyl carbon for the ring construction via an intramolecular rhodium carbenoid γ-CH insertion reaction. To test the hypothesis, campho¬lenaldehyde 95 was converted into the diazoketone 165. Treatment of the diazoketone 165 with a catalytic amount of rhodium acetate furnished the diquinane 166, via a highly regio-and stereoselective insertion of the intermediate rhodium carbenoid in the CH bond of the tertiary methyl group, which is located cis with respect to the diazoketone, Scheme 39.72 As an application of the Nazarov cyclisation mediated synthesis of the diquinane 134, enantiospecific synthesis of the analogues of capnellenes, ABC and ABD ring systems of aberraranes have been carried out. A methyl cuprate reaction on the enone 134 generated the key intermediate, the ketone 169. A ring-closing metathesis (RCM) based cyclo¬pentannulation has transformed the diquinane 169 into the analogue of capnellene 175, as well as the analogue 197 of the ABC ring system of aberrarane. On the other hand, a Wacker reaction-intramolecular aldol condensation based spirocyclohexannulation transformed the diquinane 169 into an analogue 201 of the ABD ring system of aberrarane, Scheme 40.73 Finally, degradation of the two additional carbon atoms present on the A-ring furnished the ABC and ABD ring systems 235 and 238 of aberrarane, Scheme 41.(For structural formula pl refer the abstract pdf file)

Among Nature's creation, terpenoids are more versatile and exciting compounds, and provide fertile ground for developing and testing new synthetic strategies because of their phenomenal structural diversity. The thesis entitled “Enantiospecific Synthesis of Tetraquinane Diterpenes Crinipellins” describes the first enantiospecific synthesis of norcrinipellin and crinipellins, and the tricyclic core structure of tricycloillicinone, ialibinones, and takaneones. In the thesis, the compounds are sequentially numbered (bold) and references are marked sequentially as superscripts and listed at the end of the thesis. All the spectra included in the thesis were obtained by xeroxing the original NMR spectra. Crinipellins, the first group of natural products to contain a tetraquinane carbon framework, were isolated in 1985 by the research groups of Steglich and Anke from the submerged cultures of the basidiomycete Crinipellis stipitaria. Recently, In 2010, Shen and Li also reported the isolation of four new crinipellins from the Crinipellis stipitaria 113. In the present thesis, first enantiospecific synthesis of norcrinipellin and crinipellins has been described. To begin with, (S)-campholenaldehyde was transformed into the (1R,5R)-7,8,8-trimethylbicyclo[3.3.0]oct-6-en-3-one employing an intramolecular rhodium carbenoid insertion of a diazoketone, which was then transformed into the methyl (1R,2S,6R,8S,10R)-10-methoxy-2-methyl-5-oxotricyclo[6.3.0.02,6]undecane-4-carboxylate via rhodium carbenoid promoted activation of a tertiary methyl group to generate the cis, anti, cis-linear triquinane. The triquinane obtained was then transformed into ethyl 4-[(1R,2S,6S,8S,10R)-10-methoxy-2,5dimethyl-3-oxotricyclo[6.3.0.02,6]undec-4-ene-6-yl]butanoate by a sequence of reactions including an alkylative 1,3-enone transposition, which on intramolecular Michael addition reaction followed by DBU mediated equilibration generated a 5:4 mixture of ethyl (1S,3S,5R,7R,8S,11S,12R) and (1S,3S,5R,7R,8S,11S,12S)-5-methoxy8,11-dimethyl-9-oxotetracyclo[6.6.0.01,11.03,7]tetradecane-12-carboxylates, which were transformed into (12R) and (12S)-15-hydroxy-5-methoxy-20-norcrinipellin-9-ones and (12S) and (12R)-5-methoxy-20-norcrinipell-15-en-9-ones. The methodology has been further modified and extended for the first enantiospecific synthesis of (12R) and (12S) 15-hydroxy-5-(methoxymethoxy)crinipellin-9-ones In 1995, Fukuyama and coworkers reported the isolation of tricycloillicinone from Illicium tashiroi, containing an interesting 3,4,4-trimethyltricyclo[5.3.1.01,5]undecane system. This tricyclic structure was also present in two groups of acylphloroglucinoid natural products, ialibinones and takaneones. An enantiospecific synthesis of the tricyclic core structure of tricycloillicinone, ialibinones, and takaneones have been accomplished starting from (S)-campholenaldehyde employing a transannular RCM reaction as the key step, (S)-Campholenaldehyde was converted into methyl (5R)-6,6,7-trimethyl-3-oxobicyclo[3.3.0]octa-1,7-diene-2-carboxylate via the methyl (1R,5R)-6,6,7-trimethyl-3-oxobicyclo[3.3.0]oct-7-ene-2-carboxylate, which was then transformed into (1R,3S,5S)-3-allyl-7,8,8-trimethyl-5-vinylbicyclo[3.3.0]oct6-en-3-ol containing the vinyl and allyl groups at C-1 and C-3 carbons syn to each other. Transannular RCM reaction of the hydroxy diene led to the tricyclic core structure of tricycloillicinone. Further elaboration of the side chain at C-3 position led to the tricyclic core structure of ialibinones, and takaneones.

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