Conversion of some dihalogenocyclopropanes into unsaturated ketones (original) (raw)
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Preparation and reactions of some 2,2-difunctional 1,1-dibromocyclopropanes
Tetrahedron, 2007
The synthesis of 2,2-dibromocyclopropane-1,1-dicarboxylic acids is described. Reaction of substituted 1,1-dibromo-2-acyloxymethylcyclopropanes with methyl lithium at low temperature leads to a bromine-lithium exchange and then either formal protonation to give the corresponding monobromocyclopropanes or intramolecular cyclisation to give a substituted 3-oxabicyclo[3.1.0]hexane. Oxidative ring opening of these compounds leads stereoselectively to 1,1,2,2-tetrasubstituted cyclopropanes with four functionalities on the ring.
Some Reactions of gem -Dibromocyclopropanes and Metal Carbonyls
Journal of the Chinese Chemical Society, 2012
A series of gem-dibromocyclopropanes were treated with various metal complexes. Among the metal complexes, Ru(CO) 2 (PPh 3) 3 , Ru(CO) 3 (PPh 3) 2 , and Mo(CO) 6 were able to remove a bromine atom from 1,1-dibromo-2-phenylcyclopropanes (1) to yield a series of corresponding of 1-bromo-2-phenylcyclopropanes (2). Upon the treatment of 1 with Cr(CO) 6 in DMSO, a series of allenes were obtained in good yields. The correlation between the rate of formation of allenes and the substituents on the benzene gives a negative coefficient which suggests the dibromocyclopropanes possesses as an electrophile toward to Cr(CO) 6. In the presence of Cr(CO) 6 , gem-dibromobicyclo[n,1,0]alkanes (4) in DMF or DMSO solution underwent the cleavage of carbon-bromine bond followed by ring-expansion and coupling reaction to form bicycloalkenes 7.
Stereochemistry of two new polyfunctionalizedgem-dihalocyclopropanes
Acta Crystallographica Section C Crystal Structure Communications, 2002
The two new gem-dihalogenocyclopropanes (1 H S,3R)-3-(2 H ,2 Hdichloro-1 H-methylcyclopropyl)-6-oxoheptanoic acid, C 11 H 16-Cl 2 O 3 , (2), and (1 H S,3R)-3-(2 H ,2 H-dibromo-1 H-methylcyclopropyl)-6-oxoheptanoic acid, C 11 H 16 Br 2 O 3 , (3), are isostructural. Both present two stereogenic centers at C1 H and C3. The absolute con®guration was determined by X-ray methods. The cyclopropyl rings are unsymmetrical, the shortest bond being distal with respect to the alkyl-substituted C atom. Comment Despite their high ring strain, cyclopropanes are commonly encountered among both naturally occurring and synthetic compounds. In addition, diastereoselectively substituted cyclopropanes have attracted attention as useful precursors of highly strained molecules (Boche et al., 1990; Tanabe et al., 1996) and biologically active pyrethroids (Hirota et al., 1996; Kunzer et al., 1996). Thus, the promise of their usefulness as synthetic intermediates is growing rapidly. We describe here the structure of two new polyfunctionalized dichloro and dibromo cyclopropanes, (2) and (3), which could be valuable synthons for pyrethroid derivatives.
Chemistry - A European Journal, 2001
Perspirocyclopropanated bicyclopropylidene (6) was prepared in three steps from 7-cyclopropylidenedispiro[2.0.2.1]heptane (4) (24 % overall) or, more efficiently, through dehalogenative coupling of 7,7-dibromo[3]triangulane (15) (82 %). This type of reductive dimerization turned out to be successful for the synthesis of (E)-and (Z)bis(spiropentylidene) 14 (67 %) and even of the ªthird-generationº spirocyclopropanated bicyclopropylidene 17 (17 % overall from 15). Whereas the parent bicyclopropylidene 1 dimerized at 180 8C to yield [4]rotane, dimerization of 6 at 130 8C under 10 kbar pressure occured only with opening of one threemembered ring to yield the polyspirocyclopropanated (cyclopropylidene)cyclopentane derivative 19 (34 % yield), and at the elevated temperature the poly-spirocyclopropanated 2-cyclopropylidene[3.2.2]propellane derivative 20 (25 % yield). Perspirocyclopropanated bicyclopropylidene 6 and the ªthirdgenerationº bicyclopropylidene 17 gave addition of bromine, hydrogen bromide, and various dihalocarbenes without rearrangement. The functionally substituted branched [7]triangulane 28 and branched dichloro-C 2v-[15]triangulane 32 were used to prepare the perspirocyclopropanated [3]rotane (D 3h-[10]triangulane) 49 (six steps from 6, 1.4 % overall yield) and the C 2v-[15]triangulane 51 (two steps from 17, 41 % overall). Upon catalytic hydrogenation, the perspirocyclopropanated bicyclopropylidene 6 yielded 7,7'-bis(dispiro[2.0.2.1]heptyl) (52) and, under more forcing conditions, 1,1'-bis(2,2,3,3-tetramethylcyclopropyl) (53). The bromofluorocarbene adduct 33 of 17 reacted with butyllithium to give the unexpected polyspirocyclopropanated 1,4-din -butyl-2-cyclopropylidenebicyclo[2.2.0]hexane derivative 37 as the main product (55 % yield) along with the expected ªthird-generationº perspirocyclopropanated dicyclopropylidenemethane 38 (21 % yield). Mechanistic aspects of this and the other unusual reactions are discussed. The structures of all new unusual hydrocarbons were proven by X-ray crystal structure analyses, and the most interesting structural and crystal packing features are presented.
Tetrahedron Letters, 1992
Reaction of 3-alkyl-I .2-dibromocyclopropenes with electron-rich or electron-poor alkenes in solution at 0-20 "C leads to cyclopropanes apparently derived by stereoselective trapping of a single isomer of a vinylcarbene; in the absence of an alkene, the cyclopropenes rearrange to alkynes. We have shown that 3,3-dialkyl-1,2-dihalocyclopropenes rearrange to vinylcarbenes at 0 to 20 "C and that in the case of cyclopropenes (1) there is a considerable degree of stereocontrol in the ringopening, the carbenes (2. X = Cl, OMe. Ph) being trapped by an added alkene rather than the isomeric species, (3).' (1) These reactions occurred at a much lower temperature than is typical for ring-opening of other cyclopropenes which have been reported to involve rearrangement to a vinylcarbene; for example, tetramethyl-and tetrachlorocyclopropenes and 3,3-dimethylcyclopropene require temperatures of 150-180 0C?S3*4 It was not clear what factors caused the ease of reaction and controlled the stereochemistry, and, in particular, whether both alkyl-groups on C-3 were necessary; for example, 1,3-diethylcyclopropene only ring-opens at about 180 "C.' Moreover 1-halo-and 1,2-dihalocyclopropenes having no substituent at C-3 ring-open in the gas phase to produce haloallenes;6 the mechanism of this reaction remains to be determined. We now describe the ring-opening of 3-monoalkyl-1,2-dihalocyclopropenes in solution at ambient temperature, and intramolecular trapping of the derived carbenes. The tetrabromide (5a) was prepared (68 %) by refluxing the diacid (4a)' with mercuric oxide in carbon tetrachloride and then adding bromine.* Treatment of @a) with one mol.equiv. of methyl lithium at-78 "C led to the dibromocyclopropene (6a) (70 %)?