Competitive bicyclobutane and allene formation from phenyl-substituted gem-dibromocyclopropanes
✍ Scribed by William R. Moore; John B. Hill
- Book ID
- 104222606
- Publisher
- Elsevier Science
- Year
- 1970
- Tongue
- French
- Weight
- 168 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0040-4039
No coin nor oath required. For personal study only.
✦ Synopsis
Tetraalkylsubstituted E-dibromocyclopropanes react with methyllithium to afford bicyclobutanes rather than allenas.' The intermediate cyclopropylidenes, free or complexed, must suffer sufficient steric hindrance to opening that insertion into an alpha CH bond takes precedence.'c Any factor which will lead to an increase in the Cr-C ) stretching in the transition state 1 for ring opening should tend to accelerate allene formation. A possible example of such t?' '3 I YY RIZ +-...3'.*....4.~~ '2."R 3 fX;.Cf 1 an effect follows. Treatment of 2_, the dibromocarbene adduct of l,l-diphenylpropene, with methyllithium in ether at 0" gives only 1,1-diphenylbutadiene-l,2 (2) in essentially quantitative yield.' Thus the course of reaction is the same as with the dibromocarbene adduct of trimethylethylene, only allene formation occurs; no CH insertion is observed.
Under the same conditions, dibromide 4, the dibromocarbene adduct of 2,3-