Efficient stereoselective syntheses of both (±)-juvabione and (±)-epi-juvabione by new extracyclic stereocontrol methodology

Synthesis of Quaternary Carbon Stereogenic Centers by Diastereoselective Conjugate Addition of Boron-Stabilized Allylic Nucleophiles to Enones

“…The relative stereochemistry of the major diastereomer was determined by NOE experiments with 29 (Scheme C), establishing the E -substituent of the nucleophile as anti to the methine of the cyclohexane ring. This was further confirmed since the stereochemistry of 18b , formed by reaction of Z - 17 , was established by protodeboration to known compound 35 . A proposed stereochemical model for the reaction is shown by structure A .…”

“…This was further confirmed since the stereochemistry of 18b, formed by reaction of Z-17, was established by protodeboration to known compound 35. 29 A proposed stereochemical model for the reaction is shown by structure A. Allyl carbanion addition to an enone, activated by either (pin)B−F or cesium bridge between a pinacol oxygen, 30 allows for stereoselective C−C bond formation where the nucleophile stereochemistry (R E and R Z ) is relayed to the product with high fidelity. Addition via the opposite face of the nucleophile (B) appears disfavored due to sterics.…”

Homoconjugate Addition of Organocuprate to Activated Cyclopropane and Its Application to the Synthesis of (±)-Juvabione

“…Generally, the higher-order cuprates (entries [8][9][10][11][12] were effective in this reaction, and the yield rose by the addition of a Lewis acid. The best result was obtained by the combination of higher-order cyanocuprate with trimethylsilyl cyanide 9 ) as an additive (entry 11).…”

“…Cyclopropane (7) was then treated with dilithium diviny1cyanocuprate 14 ) in the presence of trimethylsilyl cyanide in tetrahydrofuran at 2°C for 1 h to give keto ester 8 in a 73% yield. Decabomethoxylation of 8 with sodium chloride in wet dimethylsulfoxide at 160°C gave desired key intermediate 9 11 ) in a 79% yield. In summary, various conditions were examined for the reaction of the homoconjugate addition of cuprates to doubly activated cyclopropane.…”

Tandem cobalt mediated rearrangement and Pauson–Khand reaction for the synthesis of functionalised polycyclic systemsElectronic supplementary information (ESI) available: experimental procedures and data for all new compounds. See http://www.rsc.org/suppdata/cc/b2/b204616b/

“…Examination of the literature revealed that Tokoroyama has observed tertiary chlorohydrin by-product formation from a TiCl 4 promoted Sakurai reaction bearing a similar pendant olefin. 8 Based on this precedent, we suspect that the initial rearrangement of enol ether complex 2 was successful, but that the intermediate ketone-TiCl 4 complex 3 then underwent carbonyl-ene/Prins type reaction leading to complexes 4 and 5 (via the forming titanium alkoxide 3) (Scheme 3). ‡ Indeed, during the course of these investigations Coates described 9 TiCl 4 promoted chloro-Prins reactions on cyclohexanones possessing a butenyl group, mirroring the reaction of our proposed intermediate cyclohexanone 3.…”