Synthesis of isoindoloisoquinoline alkaloids. A revision of the structure of (±)-nuevamine

An easy and efficient method for the synthesis of isoindoloisoquinolines, and the assignment of a new structure for the alkaloid (±)-nuevamine are reported.     

Surface enhanced vibrational (IR and Raman) spectroscopy in the design of chemosensors based on ester functionalized p-tert-butylcalix[4]arene hosts

Surface-enhanced IR (SEIR) and Raman scattering (SERS) have been employed to study the adsorption of ester functionalized tert-butyl calix[4]arenes on Ag and Au nanostructured surfaces as well as their complexes with pyrene. The influence of adsorption and complexation with pyrene on the host calixarene structure was tested for two different calixarene molecules bearing carboethoxy groups (CH(3)CH(2)COOCH(2)-) in the low rim at positions 1,3- and 1,2,3,4-. The results obtained with SEIR were compared to those obtained with SERS, to better understand the interaction mechanism of the studied calixarenes with the metallic surfaces and the ligand as well as to investigate the structure/selectivity relationship of these two surface techniques in the analysis of recognition problems in which these ester functionalized calixarene molecules are involved.     

Synthesis and structure of new carborane-substituted cyclotriphosphazenes

The reactions of [N(3)P(3)Cl(6)] with one, two, or three equivalents of the difunctional 1,2-closo-carborane C(2)B(10)H(10)[CH(2)OH](2) and K(2)CO(3) in acetone have been investigated. These reactions led to the new spiro-closo-carboranylphosphazenes gem-[N(3)P(3)Cl(6-2n)[(OCH(2))(2)C(2)B(10)H(10)](n)] (n=1 (1), 2 (2)) and the first fully carborane-substituted phosphazene gem-[N(3)P(3)[(OCH(2))(2)C(2)B(10)H(10)](3)] (3). A bridged product, non-gem-[N(3)P(3)Cl(4)[(OCH(2))(2)C(2)B(10)H(10)]] (4), was also detected. The reaction of the well-known spiro derivatives [N(3)P(3)Cl(2)(O(2)C(12)H(8))(2)] and [N(3)P(3)Cl(4)(O(2)C(12)H(8))] with the same carborane-diol and K(2)CO(3) in acetone gave the new compounds gem-[N(3)P(3)(O(2)C(12)H(8))(3-n)[(OCH(2))(2)C(2)B(10)H(10)](n)] (n=1 (5) or 2 (6), respectively), without signs of intra- or intermolecularly bridged species. Upon treatment with NEt(3) in acetone, compound 5 was converted into the corresponding nido-carboranylphosphazene. However, the reaction of gem-[N(3)P(3)(O(2)C(12)H(8))(2)[(OCH(2))(2)C(2)B(10)H(10)]] (5) with NEt(3) in ethanol instead of acetone proceeded in a different manner to give the new compound (NHEt(3))(2)[N(3)P(3)(O(2)C(12)H(8))(2)(O)[OCH(2)C(2)B(9)H(10)CH(2)OCH(2)CH(3)]] (7). For compounds with two 2,2'-dioxybiphenyl units, gem-[N(3)P(3)(O(2)C(12)H(8))(2)[(OCH(2))(2)C(2)B(10)H(10)]] (5), (NHEt(3))[N(3)P(3)(O(2)C(12)H(8))(2)[(OCH(2))(2)C(2)B(9)H(10)]] (8), and (NHEt(3))(2)[N(3)P(3)(O(2)C(12)H(8))(2)(O)[OCH(2)C(2)B(9)H(10)CH(2)OCH(2)CH(3)]] (7), a mixture of different stereoisomers may be expected. However, for 5 and 7 only the meso compounds seem to be formed, with the same (R,S)-configuration as in the precursor [N(3)P(3)Cl(2)(O(2)C(12)H(8))(2)]. The reaction of 5 to give 8 seems to proceed with a change of configuration at one phosphorus center, giving a racemic mixture. The crystal structures of the nido-carboranylphosphazenes 7 and 8 have been confirmed by X-ray diffraction methods.     

Photogeneration of o-quinone methides from o-cycloalkenylphenols

6-Alkylidenecyclohexa-2,4-dienones (o-quinone methides II) have been generated by photolysis of 2-(2'-cycloalkenyl)phenols 1 and trapped by methanol to give the ring-opened products 2. The best results have been obtained with the cyclohexenyl derivatives 1a, 1e, and 1f. In the case of the cyclopentenyl derivative 1b, photoproduct 2b was not observed, whereas only small amounts of 2c and 2d were formed from the seven- and eight-membered ring analogues 1c and 1d. Thus, ring size appears to be a key factor in the formation of o-quinone methides. This experimental result has been rationalized by means of density-functional theory (DFT) calculations. On the other hand, phenol substitution also appears to play a role in the process. Thus, electron-withdrawing groups such as CF(3) (1f) accelerate the reaction, whereas the opposite is true for electron-donating groups such as OCH(3) (1e). This is explained by an excited-state intramolecular proton transfer (ESIPT) mechanism, as the above results are consistent with the excited-state acidities of the different phenols. The lack of reactivity in the case of ketone 1g, where the intersystem crossing quantum yield is close to unity, allows us to rule out a mechanism involving the triplet state.     

Theoretical calculations on the cycloreversion of oxetane radical cations

The molecular mechanism for the cycloreversion of oxetane radical cations has been studied at the UB3LYP/6-31G* level. Calculations support that the cycloreversion takes place via a concerted but asynchronous process, where C-C bond breaking at the transition state is more advanced than O-C breaking. This allows a favorable rearrangement of the spin electron density from the oxetane radical cation (with the spin density located mainly on the oxygen atom) to the alkene radical cation which is one of the final products. Inclusion of solvent effects does not modify the gas-phase results.