Mercury(II)-catalyzed synthesis of spiro[4.5]decatrienediones from allenyl ketones and comparison with silver(I)-, palladium(II)- and Bronsted acid-catalyzed reactions

The allenyl p-methoxybenzyl ketone 3a and allenyl p-siloxybenzyl ketones 6b selectively delivered three different products with three different transition metal-catalysts. With Hg(II)-catalysts a spiro[4.5]decene 9, with Ag(I)-catalysts a 2-substituted furan (10/11) and with Pd(II)-catalysts a 2,4-disubstituted furan (8/12) was formed. Only with perchloric acid the intermolecular addition of water to the allene, leading to 1,3-dicarbonyl compounds 7, was observed. While with the corresponding allenyl o-methoxybenzyl ketone 3b the Ag(I)- and Pd(II)-catalysts provided the expected products, the mercury-catalyst led to a new and interesting side-product rac-17 which combined both the furan moiety and the spiro[4.5]decene moiety. Efforts to prepare allenyl hydroxybenzyl ketones failed, in one case a small amount of a 5H-benzo[b]oxepin-4-one 21 was isolated. It also was not possible to extend the spirocyclization to allenyl p-siloxyphenyl ketone 6a or allenyl 2-(p-siloxyphenyl)ethyl ketone 6c.