Six Ring Oxygen Systems

Norlignans are a small group of natural products of which sequirin (76) is a typical example. A multistage synthesis of the racemic ether (77) has now been described, the key step being the stereospecific ring closure of (75) to (77) using 

Ficini, J. Besseyre, and A. Krief, Bull. Soc. chim. France, Part 2, 1976, 987. F. Cooke and P. Magnus, J.C.S. Chem. Comm., 1976, 519. 

The double ring-closure of the diazoketone (81) with phenyl acetylene gave (82) in a remarkable 86% yield the reaction was catalysed by cupric acetoacetonate and 

Syntheses of oxygen-containing natural products have employed some interesting transformations. The total synthesis of pederamide (94), the main hydrolysis product of the powerful insect poison pederin, has utilized two key ring-forming 

Motoyama, and M. Hamaguchi, Bull. Chem. Soc. Japan, 1976, 49, 2298. 

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Six Ring Oxygen Systems.—Ynamines add to cisoid-enones to give good yields of amino-y-pyrans and pyranopyrans (Scheme 28). Alkylation of the monoanion... 

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