@article{117fdee6db304f3681538bb6368b2569,
title = "[4+2] Cycloadditions of 2-(trialkylsilyloxy)-allylidenecyclopropanes - synthesis of spiro[2.5]octan-5-ones",
abstract = "The previously unknown 2-(trialkylsilyloxy)allylidenecyclopropanes 2a-d have been prepared by silyl-enolization of the easily available cyclopropylidenealkanones 1-R1 in good yields. Dienes 2a-d readily react with a variety of dienophiles at temperatures ranging from 0 to 130°C to give derivatives 5-10 of 5-(trialkylsilyloxy)spiro-[2.5]oct-4-ene or the corresponding hydrolysis products 10, 12. Weak dienophiles like cyclohexenone and cyclopentenone give spiro[2.5]octan-5-one derivatives only under BF3 catalysis and with poor yields.",
keywords = "BF catalysis, Diels-Alder reactions, Ring strain and donor activated dienes, spirocyclopropane mimic of gem-dimethyl groups",
author = "Thies Thiemann and Stephan Kohlstruk and Gerhard Schw{\"a}r and Meijere, {Armin de}",
note = "Funding Information: The deactivateda nd more highly substituted3 -acetoxy-2-methylcyclopentenonde id not react with 2a at all. In the latter reactlon the only product isolated was 17 (28% yield), apparently formed from the [4+2] cycloadduct of 2a onto 1-H arismg from hydrolysis of 2a. Although formally l,l-disubstituted, the previously unknown 2-(trialkylsilyloxy)allylidenecyclopropanes2 are activatedb oth by ring strain and donor substitution.T heir cycloadducts 5-12 can be used as a mlmlc of the correspondmg skeletons with a gem-dimethyl umt m place of the spirocyclopropaneg roup. In fact, the latter can generally be transformedi ntn a gem-dlmethyl unit by catalytic hydrogenation,a s has been demonstrateda number of tlmes.13 Acblowledgenzenfs This work was financially supportedb y the Deutsche Forschungsgemeinschaft( Projekt Me 405/14-1,2,3) and the Fonds der Chemlschen Industrie as well as BASF, BAYER, HOECHST and HtiS AG through generous gifts of chemicals Stephan Kohlstruk IS grateful to the Konrad Adenauer Foundation for a graduatef ellowship (Doktoranden-Stlpendlum).",
year = "1991",
month = jul,
day = "15",
doi = "10.1016/0040-4039(91)80812-K",
language = "English",
volume = "32",
pages = "3483--3486",
journal = "Tetrahedron Letters",
issn = "0040-4039",
publisher = "Elsevier Ltd",
number = "29",
}