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Robinson annulation of 2-hydroxymethylene-ketones. A new route to spiro-diketones
Abstract
The adducts formed from methyl vinyl ketone and the 2-hydroxymethylene derivatives of cyclic ketones of ring sizes 5, 6, 7, and 1 2 have been cyclised to spiro-ketones containing the same number of carbon atoms. Cyclisation under mild conditions gives ketols, the constitution and stereochemistry of which have been investigated. Methanol containing anhydrous calcium chloride converts the adducts of ring sizes 7 and 1 2 into spiro-ethers; the C6 adduct gives differently constituted products. The spiro-ketones all have a u.v. absorption band at ca. 224 nm (εca. 6500) but a second band of approximately the same intensity appears at 246 nm for ring sizes 5 and 12.
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