Telling the difference quickly: Femtosecond laser pulses are not only suitable to distinguish structural isomers. They also provide access to the distinction of enantiomers by combination of circular dichroism and mass spectrometry [picture: see text].
Macrocyclization between tetrathiafulvalene (TTF) dithiolates and bis-bromomethylazobenzenes/bis-bromomethylstilbenes is investigated under high dilution conditions. We show that macrocycles of different size can be formed depending on whether the (Z)- or (E)-isomers of azobenzene (AB) or stilbene are used. This represents the first example of a light-controllable cyclization reaction. The oxidation potential of the small, structurally rigid TTF-AB macrocycle is found to depend on the conformation of the AB moiety, opening the way for the modulation of redox properties by an optical stimulus. DFT calculations show that the out-of-plane distortion of the TTF moiety in this macrocycle is responsible for the variation of its oxidation potential upon photoisomerization of the neighboring AB bridge.
A five-step synthesis of the natural product angelicoin A using a late stage highly regioselective palladium(0)-catalyzed decarboxylative prenyl migration and aromatization sequence as the key step is reported. The method was extended with geranyl migration in eight-step total syntheses of hericenone J and hericenol A from geraniol.
This paper describes the total synthesis of the fungal natural product mycophenolic acid through palladium‐catalyzed allylation, biomimetic cyclization, and aromatization. Methyl (4E)‐6‐hydroxy‐4‐methylhex‐4‐enoate, which was converted in four steps into the key diketo ester dioxinone via two selective C‐acylation reactions, was transformed into a resorcylate. Subsequent phenol methylation, lactonization, iodo‐ether formation, and halogenation gave a tricyclic intermediate. Palladium‐catalyzed cross‐coupling with DABCO–(AlMe3)2 and saponification gave mycophenolic acid. An alternative approach with early stage arene methyl incorporation unexpectedly resulted in the formation of a γ‐pyrone.
A convenient and simple three step synthesis of 1,7-diazaspiro[5.5]undecane via Claisen condensation and acid catalyzed decarboxylation and spirocyclization of N-Boc-δ-valerolactam is described. Reactions of this spiroaminal with electrophiles including alkyl halides, alkane dihalides, acid chlorides, and sulfonyl chlorides gave either spirocyclic adducts or tetrahydropyridine derivatives. Additionally, the parent heterocycle is a novel bidentate ligand and formed complexes with ruthenium(II) and copper(II).
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