Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with amines: selective reaction pathways depending on the nature of the amine radical cations
with tertiary amines was investigated. Debrominated β-keto esters and ring-expanded γ-keto esters were obtained as major products. On the basis of mechanistic experiments it was concluded that these products are formed via a reaction sequence of selective carbon–bromine bond cleavage and subsequent competitive hydrogen abstraction and Dowd–Beckwith ring-expansion of the resulting primary alkyl radicals
Tris(trimethylsilyl)silane (TTMSS) promoted free radical reaction in benzotrifluoride (BTF) was investigated. Compared to same reaction using environmentally less desirable tri-n-butyltin hydride (TBTH) in benzene, less quantity of BTF than that of benzene can be used because of slower hydrogen atom transfer from TTMSS than that from TBTH toward primary alkyl radicals. Also, electron-transfer reactions
A photo-reagent system of benzimidazoline and Ru(bpy)3Cl2 to promote hexenyl radical cyclization and Dowd–Beckwith ring-expansion of α-halomethyl-substituted benzocyclic 1-alkanones
undergo 5-exo hexenyl cyclization as well as sequential cyclization and ring-expansion (Dowd–Beckwith) reactions to form radicals that abstract hydrogen atoms from the radical cation of DMBIH to yield the observed products. The results of a study of the effects of substituents located on the 2-aryl ring of DMBIH suggest that steric and hydrogen-bonding interactions influence the nature of the reaction
palladium-catalyzed Dowd–Beckwith ringexpansion/C–C bond formation cascade is described. A range of six to nine-membered β-alkenylated cyclic ketones possessing a quaternary carbon center were accessed under mild conditions. Besides styrenes, the electron-rich alkenes such as silyl enol ethers and enamides were also compatible, providing the desired β-alkylated cyclic ketones in moderate to good yields.
Photoreaction of halomethyl substituted benzocyclic ketones with amines: radical cyclization and ring expansion reactions promoted through photoinduced electron transfer processes
作者:Eietsu Hasegawa
DOI:10.1039/a703974c
日期:——
Photoreaction of ethyl 2-bromomethyl-1-oxo-1,2,3,4- tetrahydronaphthalene-2-carboxylate 1a or other related compounds 1b–d with Me3SiCH2NEt2 in aqueous MeCN afforded ethyl 5-oxo-6,7,8,9-tetrahydrobenzocycloheptene-7-carboxylate 2a or corresponding ring expansion products 2a–d respectively.