Animesh Pramanik

Analysis of geometric and strain effects in homo-Diels-Alder reactions

Molecular mechanics calculations have been carried out to quantify the key geometric and strain effects which are likely to control the homo-Diels-Alder reactivity of 1,4-dienes. The criteria considered include C1..C5 and C2..C4 distances in the diene, twist angle of the twoπ units, and the magnitude of strain increase as a result of cycloaddition. By first considering these factors in a number of nonconjugated dienes with known reactivity, the ranges of values within which the reaction is favoured are proposed. Calculations are also reported on several substrates which have not been investigated so far. Promising systems for experimental study are suggested which, in addition to being intrinsically interesting, would place the present proposals on a firm basis.

Singlet oxygen additions to hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-dien-3,10-diones. A remarkable substituent effect on π-face selectivity induced by transition state geometric distortions

Face selectivity in singlet oxygen addition to a rigid polycyclic diene is reversed by sterically neutral 1,4-substitution, an effect attributed to lone pair repulsions induced by out-of-plane bending at the transition state.

Aromatic claisen rearrangements in carbohydrates: stereocontrol of rearrangement rates in unsaturated sugar substrates

A remarkable difference is observed in the rates of [3,3]-sigmatropic rearrangement of aryl 4,6-di-O-acetyl-2,3-dideoxy-D-erythro-hex-2-enopyranosides 1 and 2; the slower reactivity of the alpha-isomers is consistent with AM1 calculated transition state energetics of model systems.

Stereoelectronic control of cope rearrangement energetics through remote double bonds in novel, rigid polycyclic frames

The presence and orientation of remote double bonds are shown to completely alter the shapes of Cope rearrangement energy profiles in a heptacyclic system.