Synthesis of tricyclic bridgehead olefins related to the core structure of CP-225,917 and CP-263,114—solvent, strain, and substitution effects on siloxy-Cope rearrangements

3,4-Homoadamantadiene: generation and regioselective [2+2] cycloaddition of a novel tricyclic bridgehead allene

Dehalogenation of 3-bromo-4-iodo-4-homoadamantene with n-BuLi gave rise to 3,4-homoadamantadiene, a novel tricyclic bridgehead allene, which readily dimerized to head-to-head and head-to-tail [2+2] cycloadducts in a ratio of 96:4. Trapping with 1,3-diphenylisobenzofuran was successful to yield the corresponding Diels-Alder adduct.

Total synthesis of the CP-molecules (CP-263,114 and CP-225,917, phomoidrides B and A). 1. Racemic and asymmetric synthesis of bicyclo[4.3.1] key building blocks

A brief introduction into the chemistry of the CP-molecules is followed by first-generation synthetic sequences toward key building blocks for their total synthesis. Processes for both racemic and enantiomerically enriched bicyclo[4.3.1] ketone 6 or its equivalent are described, and the absolute stereochemistries of the optically enriched intermediates are determined. The efficient route developed to racemic 6 and the ready access to both enantiomers of key building blocks provided the opportunity for the total synthesis of the CP-molecules and determination of their absolute stereochemistry.

Evolution of a synthetic approach to CP-263,114

[structure: see text] Three different approaches to the carbocyclic core of CP-263,114 are presented that illustrate a strategic evolution from an oxy-Cope rearrangement to variants of the Wharton fragmentation.

Reverse aromatic cope rearrangement of 2-allyl-3-alkylideneindolines driven by olefination of 2-allylindolin-3-ones: synthesis of alpha-allyl-3-indole acetate derivatives

The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces.

An exploratory study of type II [3 + 4] cycloadditions between vinylcarbenoids and dienes

The intramolecular type II [3 + 4] cycloaddition between vinylcarbenoids and furans is a practical method for the construction of 5-oxo-10-oxatricyclo[6.2.1.0(4,9)]undeca-3, 8(11)-dienes, containing two anti-Bredt double bonds. These tricyclic systems are well functionalized for eventual elaboration to the natural product CP-263,114. The rhodium-stabilized vinylcarbenoids are generated by dirhodium tetracarboxylate catalyzed decomposition of vinyldiazoacetates. The [3 + 4] cycloaddition is generally considered to occur by a tandem cyclopropanation/Cope rearrangement, although evidence is presented that with these substrates the [3 + 4] cycloaddition may occur in a concerted manner.

Studies Toward an Asymmetric Synthesis of CP-263,114 and CP-225,917

An enantioselective approach to construction of the complex framework of the CP compounds is presented. The synthesis relies on initial elaboration of the two sidechains. The "upper" appendage was asymmetrically dihydroxylated with both AD-mix reagents in order to lend flexibility to the scheme and provide the necessary handle for evolving the additional stereogenic centers. These fragments were linked to benzoic acid via Birch reduction-alkylation and subsequent cuprate addition. A series of functionalization reactions including dissolving metal reduction, Claisen rearrangement, iodolactonization, regioselective epoxide cleavage-oxidation, and intramolecular Wadsworth-Emmons cyclization took advantage of highly efficient stereocontrol. However, this flexibility was thwarted when deprotonation of a penultimate intermediate failed to be regioselective in the proper direction.