Synthesis of Bombycol
Structure of Bombycol
Synthesis:
Structure of Bombycol
Synthesis:
Paterno-Büchi Reaction
Paterno-Büchi Reaction
In this reaction photoinduced oxetane is formed by the photochemical [2+2] cycloaddition of a carbonyl with an olefin.
In this reaction photoinduced oxetane is formed by the photochemical [2+2] cycloaddition of a carbonyl with an olefin.
Mechanism:
The possible transitions (C=O) are shown below:
Once the carbonyl ground state has been photoexcited, either a singlet or triplet state may be formed:
Either type of transition (n,π* and π,π*) and electronic state (singlet, triplet) may participate in the first stage of this reaction, which is rationalized by invoking diradical intermediates:
Breaking of the new σ-bonds requires more energy, and the reverse reaction is not possible using same light frequency.
Application:
Diatropic ring | Ring currents in large [4n + 2]-annulenes
Ring currents in large [4n + 2]-annulenes
Alessandro Soncini, Patrick W. Fowler and Leonardus W. Jenneskens
Reported computational results for large [4n + 2]-annulenes indicate a falling off of aromaticity in D3h geometries but its retention in D6h geometries, as diagnosed on both energetic and magnetic criteria. Ipsocentric pseudo- mapping of the current density induced by a perpendicular external magnetic field shows that ring currents follow this trend.
Diatropic ring currents are quenched in D3h geometries but survive in D6h geometries of [4n + 2]-annulenes (4n + 2 = 30, 42, 54, 66). Ipsocentric orbital contributions explain this distinction in terms of the translational/diatropic, rotational/paratropic selection rules for current in monocycles, coupled with an account of differential angular-momentum mixing in D3h and D6h symmetries. The orbital model rationalises the differences between D6h and D3h geometries, accounts for the decay of aromaticity with ring size for D3h[4n + 2]-annulenes, and predicts trends for anti-aromatic [4n]-annulenes in the two symmetry groups.
Alessandro Soncini, Patrick W. Fowler and Leonardus W. Jenneskens
Reported computational results for large [4n + 2]-annulenes indicate a falling off of aromaticity in D3h geometries but its retention in D6h geometries, as diagnosed on both energetic and magnetic criteria. Ipsocentric pseudo- mapping of the current density induced by a perpendicular external magnetic field shows that ring currents follow this trend.
Diatropic ring currents are quenched in D3h geometries but survive in D6h geometries of [4n + 2]-annulenes (4n + 2 = 30, 42, 54, 66). Ipsocentric orbital contributions explain this distinction in terms of the translational/diatropic, rotational/paratropic selection rules for current in monocycles, coupled with an account of differential angular-momentum mixing in D3h and D6h symmetries. The orbital model rationalises the differences between D6h and D3h geometries, accounts for the decay of aromaticity with ring size for D3h[4n + 2]-annulenes, and predicts trends for anti-aromatic [4n]-annulenes in the two symmetry groups.