Ring acetylide-aldehyde

Another notable approach to the NCS chromophore nine-membered ring based upon an acetylide-aldehyde ring closure, although ultimately unsuccessful, comes from the labora-... 

We added the acetylene to aldehyde 12 now because this step is not compatible with a protected guanidine. Treatment of 43 with EtMgBr to form the acetylide and addition of aldehyde 12 afforded 54% of 45 and 32% of 44. Under the basic conditions, the secondary amine adds to the carbamate to form the oxazolidinone ring. The decrease in the geminal coupling constant of the methylene hydrogens adjacent to the nitrogen from 11 Hz in 43 to 8 Hz in oxazolidinone 45 is characteristic of the... 

The total synthesis of the marine-derived diterpenoid sarcodictyin A was accomplished in the laboratory of K.C. Nicolaou. The most challenging part of the synthesis was the construction of the tricyclic core, which contains a 10-membered ring. This macrocycle was obtained by the intramolecular 1,2-addition of an acetylide anion to an a, 3-unsaturated aldehyde. This unsaturated aldehyde moiety was installed by utilizing the Knoevenagel condensation catalyzed by (3-alanine. The Knoevenagel product was exclusively the ( )-cyanoester. 

Ring closure of ortfto-aminoaryl-alkynyl-carbinols, readily available by acetylide addition to an aryl-ketone or -aldehyde, can be achieved with copper or palladium catalysis. Comparable ort/io-nitroaryl-carbinols undergo nitro group reduction and ring closure simply by treatment with a metal/acid combination. ... 

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