Ene and retro-ene reactions in group 14 organometallic chemistry

Transition structure for the retroene-type elimination reaction of propene from allylamines

“…The same behavior is observed in the nitrogen atom, which, in order to maintain optimum orbital overlap in the transition state, is located nearly opposite the C3 carbon atom. Both C3 and N4 atoms, changing their hybridization states from sp 3 to sp 2 , show a geometry intermediate between these two states. These facts explain the geometry of the transition state.…”

“…Retroene fragmentation reactions constitute an increasingly useful tool in organic chemistry for the generation of novel double-bonded species, whose scope and broad applicability have been reviewed [1][2][3]. The application of this reaction to heteroatomic molecules has not yet been extensively studied [1][2][3]; nevertheless, it has been used for the *To whom correspondence should be addressed.…”

“…The application of this reaction to heteroatomic molecules has not yet been extensively studied [1][2][3]; nevertheless, it has been used for the *To whom correspondence should be addressed.…”

“…The allyl sulfides [7,8], on the other hand, showed a temperature-independent kinetic isotope effect [8] and an important substituent effect [7] on the rate of the pyrolysis, suggesting a polar transition state in which the higher reactivity was due to an enhanced acidic character of the ␣-H atom to be transferred in a nonlinear 1-5 shift path. For the thermal generation of silenes from allylsilanes [3,13,14], a concerted retroene elimination of propene was proposed. Thermal decomposition of allylamines [9][10][11][12] has shown that the rate of pyrolysis is dependent on the substituent on the N atom and on the acidity of the H atom likely to be transferred, suggesting a polar transition state with a, perhaps, less concerted mechanism than for the allyl ethers.…”

Tandem Zn‐Brook Rearrangement/Ene‐Allene Carbocyclization

“…[2] When both partners are simple alkenes and are linked together so as to provide for an intramolecular ene reaction, there is a preference for the formation of cis-disubstituted cyclopentane [3] and transdisubstituted cyclohexane systems. [4] However, non-catalyzed ene reactions usually require elevated temperatures, and so the intramolecular metallo-ene reaction, in which a metal atom is transferred instead of a hydrogen atom (Scheme 1, path A), represents an interesting variant.…”