โ Scribed by Stephane Bogen; Mihaela Gulea; Louis Fensterbank; Max Malacria
No coin nor oath required. For personal study only.
5-Endo-trig Radical Cyclizations of Bromomethyldimethylsilyl Diisopropylpropargylic Ethers. A Highly Diastereoselective Access to Functionalized Cyclopentanes.
-The title ethers (I), (V) and (VIII) undergo a radical-induced 5-exo-dig cyclization-diastereoselective 1,5-hydrogen transfer-5-endo-trig cyclization sequence to furnish cyclopentane derivatives (III), (VI) and (IX) with attachment of two novel stereogenic centers and fixation of Z-geometry in the intermediary formed double bond [trapped as by-product (IV)]. This reaction sequence is strongly influenced by the nature of acetylenic substituent. Thus, in the case of phenyl-substituted analogue (VIII) the final 5-endo-trig cyclization competes with a 4-exo-trig cyclizationfragmentation process to give high yields of benzylidene-substituted siloxepanes (X) besides the expected cyclopentane derivative (IX). Attempts to realize an asymmetric version of this cyclization by introduction of chiral sulfoxide or prochiral phosphoryl moieties into the acetylenic residue are not successful.
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Synthesis of Cyclic Bis(trimethylsilyl) Enol Ethers and Their [3 + 4] and [3 + 5] Annulation Reactions with Dicarbonyl Electrophiles. Access to Highly Functionalized Tricyclic Ethers Possessing trans Intrabridgehead Stereochemistry. -The title investigation is presented in connection with studies on