Butadiene reaction with dichlorocarbene

Site selectivity in a number of other concerted cycloadditions which are not [4 + 2] cycloadditions is also explained by frontier orbital control. Thus diphenylketene (332) reacts with isoprene (333) mostly at the more substituted double bond, and with cis-butadiene-l-nitrile (334) at the terminal double bond.263 Dichlorocarbene reacts at the terminal double bond of cycloheptatriene (335),264 and the Simmons-Smith reaction (336 + 337)265 also takes place at the site with the higher coefficients in the HOMO. 

In Table I are some pertinent data for a number of dichlorocarbene adducts of cis- and trans-polybutadiene. Figure 1 shows the 13C NMR spectra of three cis-polybutadiene-based adducts having widely different chlorine contents. At low percent Cl, i.e. low extent of reaction, the spectrum is essentially that of cis-polybutadiene (15) with some additional smaller resonances due to the presence of modified butadiene units (Figure 1A). With increasing chlorine content, these additional resonances grow relative to those due to... 

The reaction of carbenes with olefins to form cyclopropyl derivatives has been used to modify elastomers. Pinazzi and Levesque and Berentsvich et al. found that carbene addition had a significant influence on the properties of polydienes. Thermogravimetric analysis (TGA), flammability and oil resistance in NR and dichlorocarbene modified styrene butadiene rubber (DCSBR) blends were investigated by thermogravimetrie analysis as a funetion of different composition. The TGA plots confirmed the better thermal stability and flame resistance of DCSBR as well as its blends with NR. The amount of DCSBR in the blend significantly affected the properties of blends. 

Reaction of 1,3-butadiene [55] and 1,2-butadiene [53] systems bearing electron withdrawing groups with chloroform under alkaline phase transfer conditions results in low yields of 1,1-dichlorocyclopropanes. In these systems, dichlorocarbene generally adds to the double bond most remote from the electron withdrawing substituent. Examples are shown in equations 2.31—2.33. 

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