Rearrangement protocols mechanisms

In this paper a method [11], which allows for an a priori BSSE removal at the SCF level, is for the first time applied to interaction densities studies. This computational protocol which has been called SCF-MI (Self-Consistent Field for Molecular Interactions) to highlight its relationship to the standard Roothaan equations and its special usefulness in the evaluation of molecular interactions, has recently been successfully used [11-13] for evaluating Eint in a number of intermolecular complexes. Comparison of standard SCF interaction densities with those obtained from the SCF-MI approach should shed light on the effects of BSSE removal. Such effects may then be compared with those deriving from the introduction of Coulomb correlation corrections. To this aim, we adopt a variational perturbative valence bond (VB) approach that uses orbitals derived from the SCF-MI step and thus maintains a BSSE-free picture. Finally, no bias should be introduced in our study by the particular approach chosen to analyze the observed charge density rearrangements. Therefore, not a model but a theory which is firmly rooted in Quantum Mechanics, applied directly to the electron density p and giving quantitative answers, is to be adopted. Bader s Quantum Theory of Atoms in Molecules (QTAM) [14, 15] meets nicely all these requirements. Such a theory has also been recently applied to molecular crystals as a valid tool to rationalize and quantitatively detect crystal field effects on the molecular densities [16-18]. 

FigUre 3-12 The MaiUard Reaction. Shown are the preliminary rearrangements of functional groups (common to the proteins and sugars in DOM) that could serve as the foundation for additional cross-reactions that may occur during in situ transformations of DOM or during analytical hydrolysis protocols. This could provide a mechanism for the formation of hydrolysis resistant amides that prevent bulk and monomer level characterization of DON. 

Transition metal catalysed prenylation. There is a new one-step N-tert-prenylation of indole developed by Baran and co-workers [42] which still outcom-petes the chemoenzymatic approach (Scheme 5). Isobutene (21) as prenyl source is reacted with side-chain Fmoc-protected tryptophan methyl ester 20 in the presence of catalytic amounts of Pd(OAc)2 and superstoichiometric amounts of Ag(I) trifluoroacetate and Cu(II) acetate. The protocol also requires the presence of oxygen. After about 1 day at 35°C, the N-tert-prenylated indole is obtained in a yield of about 60%. The mechanism has not been elucidated, but may involve a 7i-allyl-Pd(II) complex which is coordinated by the indole nitrogen or by C3. In the latter case, a Pd-Claisen rearrangement of a 3-palladated indole would follow. Ag (I) functions as reoxidant of Pd(0). 

In 2003, Bols and co-workers described that the reagent IN3 can easily transform the aldehydes into the acyl azides under mild conditions (Scheme 6.22a) [76]. Furthermore, they demonstrated that the synthesis of carbamoyl azides could be realized at reflux by combining the aldehyde C-H bond azidation and flie Cuilius rearrangement in a one-pot protocol (Scheme 6.22b). A possible radical mechanism were proposed for this transformation (Scheme 6.22c). The weak I-N3 bond homolysis can initiate the chain reaction. The generated iodine radical abstracts an aldehyde hydrogen atom from the substrates to produce the acyl radical A. The acyl radical A reacts with IN3 to afford the acyl azides and iodine radical, thereby sustaining the radical chain. 

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