950-21-0Relevant articles and documents
Farina,Di Silvestro
, p. 183,184,185 (1975)
Ring strain release as a strategy to enable the singlet state photodecarbonylation of crystalline 1,4-cyclobutanediones
Kuzmanich, Gregory,Garcia-Garibay, Miguel A.
supporting information; experimental part, p. 883 - 888 (2012/01/13)
Challenging most chemists' intuition, highly reactive dialkyl biradicals can be reliably generated in the solid state by taking advantage of the photodecarbonylation of cyclic ketones. However, it has been shown that radical stabilizing groups with resonance-delocalizing abilities at the α-carbons of the precursor are required to facilitate the α-cleavage reaction, and that triplet state reactivity is essential to slow down the combination of the intermediate acyl-alkyl biradical back to the starting ketone. Relatively long triplet acyl-alkyl biradical lifetimes give a chance for the loss of CO to occur. Looking for additional strategies to generate transient biradicals in solids, we studied the solid state photochemistry of four aliphatic, dispiro-substituted 1,4-cyclobutandiones (1a-d) that were expected to react from the singlet state. We hypothesized that the release of ring strain from the small ring carbonyl would make the reverse acyl-alkyl combination disfavored, allowing for the loss of CO to occur efficiently and irreversibly. We report here the results of studies carried out in solution, bulk (powder) crystals, and nanocrystalline photochemistry. We have recently shown that excitation of dispirocyclohexyl-1,3-cyclobutanedione 1c led to the trapping of the intermediate oxyallyl with a half life of about 42 min. Our studies with the three other crystalline derivatives revealed that, while all react efficiently, the remarkably long lifetime of oxyallyl is unique to crystals of 1c.
Generation, Alkylation, and Silylation of Directed Enolates Formed by Reaction of Ketenes and Organolithium Reagents
Baigrie, Lynn M.,Lenoir, Dieter,Seikaly, Hani R.,Tidwell, Thomas T.
, p. 2105 - 2109 (2007/10/02)
Symmetrical ketenes R2C=C=O R2=t-Bu2(1), Et2(2),(CH2)4(3),(CH2)5(4) were reacted with organolithium reagents R'Li to give directed enolates R2C=C(OLi)R' which were alkylated with MeI or silylated with Me3SiCl.The silylation results for 2-4 were compared to those for reaction of ketones R2CHCO-n-Bu (16-18) with Me3SiCl and either i-Pr2NLi, KH, or Et3N.These latter conditions usually favored different regioisomers from the ketene route.Reaction of 1 with t-BuLi gave the previously inaccessible enolate t-Bu2C=C(OLi)-t-Bu (25), which on reaction with MeI gave a mixtureof the O-methylation product 27 along with some C-methylation product and with Me3SiCl gave the silyl enol ether 26.The vinyl ethers 26 and 27 are among the first substituted tri-tert-butylethylenes which have been reported.
