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A new triterpene 1a from Achillea odorata L. has been isolated, and its structure established on the basis of its spectroscopic properties as well as those of its acetylderivative 1b. 1a shows the first example of monocyclic triterpene skeleton, biosynthetized in the first step of cyclization of squalene oxyde.

A total synthesis of (±)-pinidine I was accomplished starting from the readily available propargylic tosylate 1 and 5-bromo-2-pentanone 2.

By an appropriate choice of cation, three of the four possible aldols from the reactions of the chiral α-silyloxy ketone 1 with aldehydes may be obtained. The Z , lithium enolate provides 6, the Z , boron enolate gives 7, and the E magnesium enolate affords 8.