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A stereoselective strategy for the replacement of the 1,2-dihaloalkene bridge of tetrahalonorbornyl derivatives by an oxygen bridge involving stepwise controlled oxidation, cleavage of the dione thus formed, and reiterative intramolecular S(sub N)2 displacement of two bridgehead halogens is devised. The synthesis of four highly strained pentacyclic bis-oxa-bridged derivatives with interesting structural variations is presented.

Research has been conducted on the gamma-lactone-fused cyclopentanoids. The effect of the tetrahalonorborene derivatives' structural flexibility and stereochemical control on these cyclopentannulated gamma-lactones has been investigated and the details are described.

A simple computational model explains and predicts pi-facial selectivity in nucleophilic additions to sterically-free carbonyls. The model, based on MNDO, uses two sets of calculations. One measures electrostatic and polarization effects using a test charge to represent the nucleophile, while the other models the hydride ion to determine the added role of orbital interactions. Using these two, the approach is able to reproduce most empirically-established selectivities, especially with the hydride model.

Stereoselective formal synthesis of (_)-neplanocin A from a cyclopentane derivative is described by using an elegant strategy involving reiterative usage of an already existing acetonide protecting group. The acetonide protecting groups that is carried forward intact right from the starting adduct to an advanced intermediate is shuffled around twice as in a relay race through the synthetic sequence, which has avoided unnecessary employment of additional protecting groups.

A study aimed to achieve a short and stereoselective route to the trans-hydrindane derivative, which is a potential building block for the synthesis of steroidal and related molecules. The desired results were obtained by the operation of indium, tin, and ruthenium based reagents, starting from a tetrabromo norbornyl derivative.

Research has been conducted on 7-azaspiro[4.5]decan-6-ones. The authors describe the access to these compounds which involves regio- and chemoselective reactions and starts from tetrabromonorbornyl derivatives.

An unusual route for the synthesis of functionalized cyclobutane derivatives starting from functionalized norbornane derivatives is reported. Base-induced fragmentation of an oxetanol-type moiety embedded in a tetracyclic norbornyl ketal leads to a cyclobutane-fused derivative as the major or exclusive product. The fragmentation reaction for bridgehead-bromine-substituted derivatives was much faster than for the corresponding chlorine-substituted substrates. The functionalized cyclobutane product was formed exclusively in high yield in the former case, while the latter furnished a minor uncyclized side product in varying yields. [ABSTRACT FROM AUTHOR]

Total synthesis of the published structure of amathamide D is described. Methyl 2,3,4-tribromo-5-hydroxybenzoate was selected as starting compound because it is readily accessible via acid-mediated Grob fragmentation--aromatization reaction of 1,4,5,6-tetrabromo-7,7-dimethoxybicyclo[2.2.1]hept-5-en-2-one. The aforementioned ester was transformed into the reported structure of amathamide D through methylation of a hydroxyl group and conversion of the ester moiety to a β-aminoethyl side chain. The NMR data of the synthetic compound did not conform to the reported natural product structure possessing contiguously positioned β-aminoethyl side chain, a set of three adjacent bromines, and a methyl ether linkage on the phenyl ring. This prompted us to redeBne the natural product structure by synthesizing a product whose spectral data exactly matched with the reported data of amathamide D. The convolutamine H, with completely substituted phenyl ring adorned with an extra methyl ether functional group, has also been synthesized by application of Grob fragmentation--aromatization strategy to 3-(benzyloxy)-1,4,5,6-tetrabromo-7,7- dimethoxybicyclo[2.2.1 ]hept-5-en-2-one. This approach furnished directly methyl 2,3,4-tribromo-5,6-dimethoxybenzoate, which was converted straightforwardly into convolutamine H. Further, synthesis of convolutamine F and lutamide A and C is also described. [ABSTRACT FROM AUTHOR]

An efficient acid-catalyzed Grob fragmentation of symmetrical and asymmetrically substituted norbornyl a-diketones to the corresponding six-membered a-ketoenols is reported. The regio- and stereochemical outcome of the Grob fragmentation of C2 mono- and disubstituted a-diketones was investigated. A single regioisomer resulting from a favorable half-chair intermediate was normally observed. A departure from the normal course was noticed for C2 disubstituted a-diketones possessing an exo-methyl and an endo-methoxycarbonyl derivative, giving the opposite regioisomers due to initial formation of the hemiketal. The bromo analogues of the C2 disubstituted a-diketones furnished an unusual byproduct, which appears to have been formed through highly reactive fused four-membered bicyclo[2.2.0]hexane intermediates. A plausible mechanistic proposal involving the gem-dihalo intermediate, which in one case was actually isolated as its BF2-complex, is outlined. The fragmentation protocol was applied to various norbornyl substrates including bis-a-diketone derivatives. The methodology was successfully utilized for the synthesis of substituted aromatic compounds. [ABSTRACT FROM AUTHOR]

Examines the method for easy access to γ-lactone-fused cyclopentanoids. Use of lead and alkaline to cleave the tricyclic α-keto hemiacetals; Elaboration of α-keto hemiacetal 3b to spiroepoxide derivative; Transformation of α-halo ester moiety.

An unusual route for the synthesis of functionalized cyclobutane derivatives starting from functionalized norbornane derivatives is reported. Base-induced fragmentation of an oxetanol-type moiety embedded in a tetracyclic norbornyl ketal leads to a cyclobutane-fused derivative as the major or exclusive product. The fragmentation reaction for bridgehead-bromine-substituted derivatives was much faster than for the corresponding chlorine-substituted substrates. The functionalized cyclobutane product was formed exclusively in high yield in the former case, while the latter furnished a minor uncyclized side product in varying yields.

Stereoselective formal synthesis of (+/-)-neplanocin A from a cyclopentane derivative employing an elegant strategy involving reiterative usage of an already existing acetonide protecting group is reported. The acetonide protecting group that is carried forward intact right from the starting adduct to an advanced intermediate is shuffled around twice as in a "relay race" through the synthetic sequence, thus avoiding unnecessary employment of additional protecting groups.