Dipropynyl ethers

Further manipulations of 123 afforded vitamin Be (124). Unfortunately, the key cyclotrimerization was based on a high load of CpCo(CO)2 catalyst and therefore was less efficient economically. However, a recent improvement in this sequence involved the light-promoted cyclization (300 to 800 nm) of a related 3,3 bis-silyl-2-dipropynyl ether and acetonitrile in the presence of a truly catalytic amount (1 mol %) of CpCo(cod) acting as the catalyst [36c], Advantages of this modified protocol... 

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