Bicyclo octane system, formation

Similar procedures are also successful in the construction of cyclobutane rings in other stereochemical environments, including the formation of bicyclo[3.1.1]heptane (67)and bridged tricyclic systems such as (68), (69) ° and (70). ° A variety of annelated cyclobutanes have been prepared by the photochemical procedure as above, yields are sometimes poor or only moderate. Examples include bicy-clo[2.1.0]pentanes (71), °° bicyclo[2.2.0]hexanes (72)"° and cyclobuteno aromatics (e.g, 73), " o-nor-steroids e.g. 74)," A-bisnorsteroids" and triterpenes" as well as the highly strained tricyclo[4.2.0.0 ]octane system (75)," and the [4.4.4.5]fenestrane (76)." ... 

The labelling studies described above provide definitive evidence for the mixed polyketide-terpenoid biogenesis of the andibenins, andilesins, andi-tomins, austin and terretonin. The formation of the bicyclo [2.2.2] octane system in the first two classes of metabolite provides a rare example of a biosynthetic Diels-Alder reaction. The biosynthetic relationship of austin and andibenin was supported by the isolation of austin from another mutant strain of A. variecolor [81]. Further metabolites related to austin have been isolated from Emericella dentata [82] and Penicillium diversum [81]. Other complex metabolites which are almost certainly further products of the meroterpenoid pathway are fumiga-tonin (102) and paraherquonin (103) which have been isolated from Aspergillus... 

XXXVII (828, 1586, 1638 cm i, A, ax 282 mp. shifting to 300 mp. in alkali), and a keto y-lactone (1796, 1734, 1639 cm i). Formation of the latter, involving displacement of bromine a. to the keto group by carb-oxylate anion demonstrates a 1,4-relationship of the ketone and carboxyl groups in XXXVI. Thus these results, when taken with Jacobs dehydrogenation evidence for substitution at C-12 (20, 21), show clearly that a bicyclo[2.2.2]octane system is present in atisine and that the terminal... 

The C —Br bond is ionized without the participation of the C —C bond to form the classical ion 318. Thus, if the arising cation centre at in the bicyclo-[3,2,l]octane system can be stabilized by the classical p,7t-interaction, the non-classical participation does not manifest itself (cf. besides, the homobenzylic participation would result in the antiaromatic (4jt-electrons) destabilized cation 319 (cf. But in the ion 315 the arising secondary cation centre can be effectively stabilized only by the nonclassicai a- or 7t-participation formating ion 316 of the bishomoaromatic type. 

A skeletal rearrangement of bicyclo[3.3.1]nonane-2,4,9-trione to the bicyclo[3.3.0] octane system is induced by an intramolecular Michael addition (Scheme 212). ° Anilines have been synthesised by a metal-free C-N bond formation accompanying eliminative cleavage through combined aryl C-O and amide C-N bond breakage (Scheme 213). ° ... 

For other substrates, formation of a more stable cationic species drives the [1,2] shift reaction, although thermodynamic partitioning of cationic intermediates and/or subsequent rearrangements can lead to complex product mixtures10. For systems where equilibration of an initially formed cation would be expected to yield mixtures, such as methyl 5-hydroxy-7-trimethylsilyl-bicyclo[2.2.2]octane-2-carboxylates, selective bond migration has been effected by the introduction of a silyl substituent, which serves the dual role of stabilization of the fi carbocation and subsequent elimination to yield an olefinic product14. 

Heats of formation are calculated as a sum of the bond energies and other stabilizing and destabilizing (e.g., strain) increments for the structure. MM4 calculations include terms for contributions of higher-energy conformations. For a set of hydrocarbons ranging from methane and ethane to adamantane and bicyclo[2.2.2]octane, the heats of formation are calculated with a standard deviation of 0.353 kcal/mol. The MM4 system has also been applied to alkenes, ° aldehydes, and ketones. ... 

The Weiss-Cook reaction entails the formation of c/5-bicyclo[3.3.0]octane ring systems from the condensation of 1,2-dicarbonyl compounds with 3-oxoglutarate diester derivatives. Decarboxylation of the immediate reaction product affords access to the parent carbon scaffold. 

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