Preparation, modification, and evaluation of cruentaren A and analogues.

An expeditious total synthesis of the highly cytotoxic F-ATPase inhibitor cruentaren A (1) is described based on a ring-closing alkyne metathesis (RCAM) reaction for the formation of the macrocylic ring. Other key transformations comprise a C-acylation of the benzyl lithium reagent derived from orsellinic acid ester 9 with Weinreb amide 7, a CBS reduction of the resulting ketone 10, and a Soderquist propargylation of aldehyde 21 with allenylborane (S)-27 to set the C-15 chiral center of the required alcohol fragment 25. The RCAM precursor 33 was assembled by acylation of 25 with acid fluoride 32, since more conventional methods for ester bond formation were unproductive.

Molybdenum nitride complexes with Ph3SiO ligands are exceedingly practical and tolerant precatalysts for alkyne metathesis and efficient nitrogen transfer agents.

The molybdenum nitride complex [(Ph(3)SiO)(3)Mo[triple bond]N] (10), which can be conveniently prepared in situ from readily available [(Me(3)SiO)(2)((Me(3)Si)(2)N)Mo[triple bond]N] (9) and Ph(3)SiOH, and the pyridine adduct of 10, [(pyridine)(Ph(3)SiO)(3)Mo[triple bond]N] (11), exhibit excellent catalytic activity in alkyne metathesis reactions of all kinds. Adduct 11 is sufficiently stable to be weighed in air and is therefore much easier to use than any of the established, structurally defined alkyne metathesis precatalysts known to date. This new system is compatible with a host of functional groups, including esters, amides, alkenes, carbamates, ethers, silyl ethers, sulfonates, thioethers, THP acetals, glycosides, ketones, enoates, thiophenes, pyridines, thiazoles, and nitro groups, and even accepts protected propargyl alcohols as substrates.

Structural and electronic analysis of lanthanide complexes: reactivity may not necessarily be independent of the identity of the lanthanide atom--a DFT study.

Density functional theory calculations were used to study a given complex for the whole series of lanthanide cations: [Ln(C3H5)Cp(OMe)] (1) [Ln = La (Z = 57)-Lu (Z = 71)], the radioactive lanthanide promethium (Z = 61) excepted. Contrary to the common assumptions, the calculations suggested a significant, albeit indirect, contribution of f electrons to bonding. Relativistic effects were considered in the calculations of the bonding energies, as well as in geometry optimizations in both spin-restricted and unrestricted formalisms.