Effects of Aromatic Substitutions on the Photoreactions in Mg•+(C6HnF2X4-n) (X = F, CH3) Complexes: Formation and Decomposition of Benzyne Radical Cations

C-F bond activation of trifluoroethanol and trifluoroacetic acid catalysed by the dimolybdate anion, [Mo2O6(F)]- †

Two gas-phase catalytic cycles involving C-F bond activation of trifluoroethanol and trifluoroacetic acid were detected by multistage mass spectrometry experiments. A binuclear dimolybdate centre [Mo₂O₆(F)]^- acts as the catalyst in each cycle. The first cycle, entered via the reaction of [Mo₂O₆(OH)]^- with trifluoroethanol and elimination of water to form [Mo₂O₆(OCH₂CF₃)]^-, proceeds via four steps: (1) oxidation of the alkoxo ligand and its elimination as aldehyde; (2) reaction of [Mo₂O₅(OH)]^- with trifluoroethanol and elimination of water to form [Mo₂O₅(OCH₂CF₃)]; (3) decomposition of the alkoxo ligand via loss of 1,1 difluoroethene; and (4) reaction of [Mo₂O₆(F)]^- with a second equivalent of trifluoroethanol to regenerate Mo₂O₆(OCH₂CF₃)]^-. Steps (2) and (3) do not occur at room temperature and require collisional activation to proceed. The second cycle is entered via the reaction of [Mo₂O₆(OH)]^- with trifluoroacetic acid and elimination of water to form [Mo₂O₆(O₂CCF₃)]^- and involves two steps only: (1) fluoride transfer to a molybdenum centre to form [Mo₂O₆(F)]^-; (2) reaction of [Mo₂O₆(F)]^- with trifluoroacetic acid and loss of water to regenerate [Mo₂O₆(O₂CCF₃)]^-. Comparisons are made with the chemistry of [Mo₂O₆(OH)]^- reacting with acetic acid.

A Novel Crystallization-Induced Diastereomeric Transformation Based on a Reversible Carbon−Sulfur Bond Formation. Application to the Synthesis of a γ-Secretase Inhibitor

This paper describes a remarkably efficient process for the preparation of gamma-secretase inhibitor 1. The target is synthesized in only five steps with an overall yield of 58%. The key operation is a highly selective and practical, crystallization-driven transformation for the conversion of a mixture of tertiary benzylic alcohols into the desired sulfide diastereomer with 94:6 dr. This unprecedented process is based upon a reversible carbon-sulfur bond formation under acidic conditions.

Pyridyne radical cations produced by photodissociation of Mg˙+(multifluoro-pyridine) complexes: A combined experimental and theoretical study

Gas phase complexes Mg*+ (2,6-difluoropyridine) (1) and Mg*+ (pentafluoropyridine) (2) have been subjected to photodissociation in the spectral range of approximately 230-440 nm. Except for the evaporative photofragment Mg*+ , the primary photoproduct for is C(5)H(3)N*(+), which is associated with the rupture of two C-F bonds by the photoexcited Mg*+ , forming very stable MgF(2). In contrast, the direct loss of MgF(+) is more favorable for due to fluorine substitution. Given enough energy, C(5)H(3)N*(+) can undergo decomposition to form C(4)H(2)*(+) and HCN. These results are very different from those for Mg*+ (2-fluoropyridine), highlighting the significance of the additional F at C6 of and . Density functional theory (DFT) calculations have been employed to examine the geometries and energetics of the complexes as well as relevant reaction mechanisms. All of the complexes feature the direct attachment of Mg*+ to the N atom. The key intermediate is found to be FMg(+) (C(5)H(x)F(4-x)N) (x = 3 or 0), which can lead to the formation of MgF(+) directly or MgF(2) through activation of another C-F bond adjacent to N, producing the pyridyne radical cations. However, hydrogen-transfer prior to the rupture of the second C-F bond followed by ring-opening of C(5)H(3)N*(+) may result in the formation of chain forms of C(5)H(3)N*(+). The influence of the fluorine substitution on the competition of the two routes have been demonstrated.

Experimental and Computational Studies of Intracomplex Reactions in Mg+(Primary, Secondary Alkylamine) Complexes Induced by Photoexcitation of Mg+

We report herein a comprehensive study of photoinduced reactions in complexes of Mg+ with primary (n-propyl- and isopropylamine) and secondary amines (dipropyl- and diisopropylamine) in the spectral range of 230-440 nm. Similar to the methyl- and ethylamine complexes studied previously, N-H bond activation of these complexes is very unfavorable. Instead, the C(alpha)-C, C-N, and C(alpha)-H bond-cleavage photoproducts are observed after photoexcitation of the Mg+ complexes (3(2)P<--3(2)S). For Mg+(primary amine) complexes, for example, Mg+-NH2CH2CH2CH3, and Mg+-NH2CH(CH3)2, the photoproducts resulting from C(alpha)--C rupture prevail after P(z) and charge-transfer excitations, whereas the Mg+ photofragment is predominant upon P(x,y) excitation. However, with further N-alkyl substitution, as in Mg+(secondary amine) complexes, for example, Mg+-NH(CH2CH2CH3)2 and Mg+-NH[CH(CH3)2]2, a novel intracomplex C-C coupling photoreaction dominates on P(x,y) excitation of Mg+, which is believed to arise from Mg+* insertion into the C-N bond. With P(z) and charge-transfer excitation, the Mg-R elimination photoproducts, arising from C(alpha)-C bond cleavage, predominate. The energetics and possible mechanisms of the intracomplex photoreactions are analyzed in detail with the help of extensive quantum mechanics calculations.

Fluorine-substitution induced switching of dissociation patterns of C6H4*+ produced by photoelimination of MgF2 from the complexes of mg*+ (multifluorobenzene)

Complexes of fluorinated benzenes (o-C6H4-nF2+n) and Mg*+ are subjected to ultraviolet photodissociation (260-340 nm), producing efficiently benzyne radical cations (C6H4-nFn*+) besides Mg*+ and MgF+. We show that the consecutive dissociation of C6H4-nFn*+ follows the [C4(+) + C2] pattern exclusively for n < or = 2 after the parent complexes absorb one or two photons. However, the dissociation pattern is switched to [C5(+) + C1] and [C1 + C5] for n > or = 3. In particular, upon two-photon absorption at 340 nm by the complexes of Mg*+ (C6HF5) (1) and Mg*+ (C6F6) (2), photoproducts of CF+, C5H+, and C5HF*+ from C6HF3*+ and CF+, C5F+, C5F2*+, and C5F3+ from C6F4*+ are detected, respectively. Theoretical calculations are used to explain the switching of the dissociation patterns induced by the fluorine substitutions. It was found that the formation of C5+ + C1 is energetically more favorable than that of C4(+) + C2 from C6HF3*+ and C6F4*+ and of C1(+) + C5. Except for C5H2F(+) + CF, all the channels of [C5(+) + C1] and [C1(+) + C5] are energetically less favorable than those of [C4(+) + C2] from C6H3F*+ and C6H2F2*+. In most cases, the calculated results agree well with the experimental observations.