Trans-1,2-Dibromocyclopropane

Turning to cyclic compounds we see that there are three not four stereoisomeric 1 2 dibromocyclopropanes Of these two are enantiomeric trans 1 2 dibromocyclo propanes The cis diastereomer is a meso form it has a plane of symmetry... 

Trans-selective alkylation of dibromocyclopropanes via a bromochlorocyclopropane synthesis of trans- 1-butyl-2-[(phenylmethoxy)methyl]cyclopropane (Structure 22)8c... 

When each stereoisomeric reactant forms a different stereoisomeric product the reaction is known as stereospecific reaction. For example, the addition of CBr2 (dibromo-carbene, prepared from bromoform and base) to ds-2-butene gives cis-2,3-dimethyl-l,l-dibromocyclopropane (1.32), whereas addition of CBr2 to the trans-isomer exclusively yields the trans-cyclopropane 1.33. 

Hunsdiecker reaction of the silver salts of both cis-(56) and trans-2-methylcyclopropanecarboxylic acid (57) yielded the same mixture of cis- (58) and trans-1-bromo-2-methylcyclopropane (59), thus demonstrating that the 2-methylcyclopropyl radical was incapable of maintaining its configuration . Brominative decarboxylation of the silver salts of exo- (60) and em/o-norcarane-7-carboxylic acid (61) produced the same mixture (16 84) of exo- (62) and entio-7-bromonorcarane (63)". Similarly, cis- and trans-silver 1,2-cyclopropanedicarboxylate gave rise to the same isomer ratio (24 76) of cis- and fraws-1,2-dibromocyclopropane. Consistent with these results is the report that the Hunsdiecker reaction with the silver salt of trans-2,2,3-d3-cyclopropanecarboxylic acid (64) gives an equimolar mixture of cis- (65) and rrans-2,2,3-d3-cyclopropane (66) . 

Acylcyclopropanecarboxylic acids 15 are degraded by a Hunsdiecker reaction using red mercuric oxide and bromine to mixtures of trans- and cw-2-bromocyclopropyl alkanones in good to moderate yields. Similarly, 2-acetylcyclopropane-l,l-dicarboxylic acid and trans-cyclo-propane-l,2-dicarboxylic acid are transformed into 2-acetyl-l,l-dibromocyclopropane and /ran.j/c -l,2-dibromocyclopropane in 86.5 and 64% yield, respectively. ... 

To a stirred solution of the 1,1-dibromocyclopropane (5.0 mmol) and a nucleophile (11 mmol) in freshly distilled DMF (12 mL) was added dry tetracarbonyinickel (30 mmol) at rt. The mixture was stirred at elevated temperature, usually 70°C, for 3 h. Excess of tetracarbonyinickel was removed under reduced pressure. Et20 (15 mL) and 5% aq HCl (15 mL) were added to the resultant mixture, which was stirred at rt for 1 h and extracted with Et20 (3 x 10 mL). The combined organic layers were washed with brine, dried (Na2S04), and concentrated. The residue was purified by flash chromatography to give a mixture of cis- and tran -cyclopropanecarboxylic acid derivative. 

Research trends of the last few years highlight applications to more involved systems either from the substrate/product side or from the catalyst side. Furthermore, a deeper insight into underlying mechanism is intended. Thus, reductive carbonylation of dibromocyclopropanes was performed in toluene/5 M KOH with syngas (CO/H2, 3 1) at elevated temperature (90 °C) using a mixture of CoCl2, KCN, and Ni(CN)2 for the metal catalyst and PEG-400 as PT catalyst which was much more efficient than a quaternary ammonium catalyst [81]. l,l-Dibromo-2-phenylcydopropane furnished a 72% yield of 2-phenylcydopropanecarboxylic add (1 1 cis/trans mixture). 

Entries 1 and 2 are typical of concerted syn addition to alkene double bonds. On treatment with peroxyacetic acid, the cw-alkene affords only the cw-oxirane, while the trans-alktnc affords only the /rans-oxirane. Similarly, addition of dibromocar-bene to c/5-2-butene yields exclusively d5-2,3-dimethyl-l,l-dibromocyclopropane, and only rran5-2,3-dimethyl-l,l-dibromocyclopropane is formed from trans-2-butene. It should be noted that there are numerous examples of stereospecific anti addition to alkenes as well, as will be seen in Chapter 6. 

Isagawa, K., Mizuno, K., Sugita, H., and Otsuji, Y., General and convenient route to alkenylidenecy-clopropanes generation of alkenyhdenecarbenes from 1,1-dibromocyclopropanes under phase-transfer conditions, /. Chem. Soc., Perkin Trans. 1, 2283, 1991. 

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