Type II intramolecular [2 + 2]-cycloaddition of alkenes with vinylketenes prepared by the regiospecific deprotonation of .beta.,.beta.-disubstituted .alpha.,.beta.-unsaturated acid chlorides
Syntheses of bicyclo[3.3.0]octanes and bicyclo[4.3.0]nonanes by ring expansion of isopropylidenecyclobutanes
作者:Runa Berg Østby、Yngve Stenstrøm
DOI:10.3998/ark.5550190.p008.383
日期:——
subjected to HBr/HOAc in polar solvents like acetic acid, 6-(1-methylethylidene)bicyclo[3.2.0]heptanes undergo a ring expansion reaction yielding 2-bromo-3,3dimethylbicyclo[3.3.0]octane and 3-bromo-2,2-dimethylbicyclo[3.3.0]octane. Several other isopropylidenecyclobutanes have been found to undergo the same reaction with high stereoselectivity and moderate regioselectivity. In less polar solvents like
tested in the microbial reduction of methyl-substituted bicyclo[3.2.0]hept-3-en-6-ones 1a-c. The endo-alcohols 2a-c were obtained with good yields and enantiomeric excess. Lower yields are described for the exo-alcohols 3a-c which are normally enantiomerically pure. Comparisons with microbial reduction of bicyclo[3.2.0]hept-2-en-6-one 1d and bicyclo[3.3.0]oct-7-en-2-one 1e are also reported.
Practical preparation of bicyclo[3.2.0]hept-3-en-6-ones and its utilisation in stereoselective total synthesis of grandisol and lineatin via a versatile intermediate.
devised for racemic grandisol and lineatin, two important components of pheromonic blends. They are based on the utilisation of 1,4-dimethylbicyclo[3.2.0]hept-3-en-6-one as a pivotal intermediate. This compound, as well as other bicyclo[3.2.0]hept-3-en-6-ones, are now easily available by a practical bicyclization of the corresponding 3-hydroxy-6-alkenoic acids.
performed on bicyclo[3.2.0]hept-3-en-6-ones and on bicyclo[3.2.0]hept-2-en-6-one. 3,3a,4,6a-Tetrahydro-2H-cyclopenta[b]furan-2-ones, important starting materials in the synthesis of linear condensed triquinane sesquiterpenes, have been prepared in an efficient manner by the easy bicyclization of 3-hydroxy-6-heptenoic acids, followed by a Baeyer-Villigeroxidation of the bicyclo[3.2.0]hept-3-en-6-one
bicyclo[3.2.0]hept-3-en-6-ones (1a−f) have been converted into the corresponding bicyclo[3.2.0]heptane-2-endo,7-endo-diols (4a−f) in an efficient and stereoselective fashion. This preparation opens a route to a family of 1,3-diols with a chiral rigid backbone, potentially suitable as nonracemic precursors for bidentate ligands in asymmetric synthesis.