Total Synthesis of Marine Polycyclic Ethers

Improved electrochemical and thermal properties of nickel rich LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode materials by SiO 2 coating

Numerous methods have been developed for the introduction and selective removal of silicon-containing protecting groups, which are used extensively in organic synthesis.2-4 Nevertheless, there remains a great need for the development of ever milder and more selective methods for silyl group deprotection for use with baseand/or acid-sensitive substrates. Herein, we report the use of TAS-F [tris(dimethylamino)sulfonium difluorotrimethylsilicate, (Me2N)3S+ F2SiMe3] for the deprotection of a range of silyl ethers and 2-(trimethylsilyl)ethyl carbamates and esters. Particularly striking are the TAS-F-mediated deprotections of the base-sensitive substrates 1, 3, 5, 11, and 13, which could not be deprotected cleanly or efficiently by using tetra-nbutylammonium fluoride (TBAF).

Tris(dimethylamino)sulfonium Difluorotrimethylsilicate, a Mild Reagent for the Removal of Silicon Protecting Groups

allylic alkylation asymmetric ringclosing metathesis copper ruthenium N-heterocyclic carbenes desymmetrization D . G . G I L L I N G H A M , A . H . H O V E Y D A * ( B O S T O N C O L L E G E , CH E S T N U T H I L L , U S A ) Chiral N-Heterocyclic Carbenes in Natural Product Synthesis: Application of Ru-Catalyzed Asymmetric RingOpening/Cross-Metathesis and Cu-Catalyzed Allylic Alkylation to Total Synthesis of Baconipyrone C Angew. Chem. Int. Ed. 2007, 46, 3860-3864.

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Chiral N-heterocyclic carbenes in natural product synthesis: application of Ru-catalyzed asymmetric ring-opening/cross-metathesis and Cu-catalyzed allylic alkylation to total synthesis of baconipyrone C.

The first total synthesis of (-)-gambierol (1), a marine polycyclic ether toxin, has been achieved. Key features of the successful synthesis include (1) a convergent union of the ABC and EFGH ring fragments (5 and 6, respectively) via our developed B-alkyl Suzuki-Miyaura cross-coupling strategy leading to the octacyclic polyether core 4 and (2) a late-stage introduction of the sensitive triene side chain by use of Pd(PPh(3))(4)/CuCl/LiCl-promoted Stille coupling. The ABC ring fragment 5 was synthesized in a linear manner (B --> AB --> ABC), wherein the A ring was formed by intramolecular hetero-Michael reaction and the C ring was constructed via 6-endo cyclization of hydroxy epoxide 7. An improved synthetic entry to the EFGH ring fragment 6 is also described, in which SmI(2)-induced reductive cyclization methodology was applied to the stereoselective construction of the F and H rings, leading to 6 with remarkable overall efficiency. Stereoselective hydroboration of 5 and subsequent Suzuki-Miyaura coupling with 6 provided endocyclic enol ether 45 in high yield, which was then converted to octacyclic polyether core 4. Careful choice of the global deprotection stage was a key element for the successful total synthesis. Functionalization of the H ring and global desilylation gave (Z)-vinyl bromide 2. Finally, cross-coupling of 2 with (Z)-vinyl stannane 3 under Corey's Pd(PPh(3))(4)/CuCl/LiCl-promoted Stille conditions completed the total synthesis of (-)-gambierol (1).

and D. Scott Coffey

Papers

Tris(dimethylamino)sulfonium Difluorotrimethylsilicate, a Mild Reagent for the Removal of Silicon Protecting Groups

Total synthesis of (+)-damavaricin d