Stereoselective Total Synthesis of Aspergillide A: A Visible Light-Mediated Photoredox Access to the Trisubstituted Tetrahydropyran Core.

A stereoselective total synthesis of natural product aspergillide A is reported. The adopted strategy relies on the direct access to the key tetrahydropyran core through a visible light-mediated photoredox reaction from an allylic alcohol and iodoacetic acid. In a single manipulation, a γ-iodo-δ-valerolactone is obtained through an atom transfer radical addition followed by in situ acid-catalyzed lactonization. The obtained lactone possesses three functionalized sites, which were seized to link the required substituents in the final product and thus completing the total synthesis of aspergillide A.

Visible-Light Photocatalytic Preparation of 1,4-Ketoaldehydes and 1,4-Diketones from α-Bromoketones and Alkyl Enol Ethers.

A Ru2+-photocatalyzed, visible-light-mediated ATRA reaction for the straightforward preparation of 1,4-ketoaldehydes, 1,4-diketones, and 1,4-ketoesters, which are of difficult access by other means, is reported herein. This method employs readily accessible α-bromoketones and alkyl vinyl ethers as starting materials, allowing the construction of secondary, tertiary, and challenging quaternary centers. In addition, the synthetic usefulness of this method is illustrated by applying it to the construction of substituted pyrroles.

Three tetracyclic dibenzoazepine derivatives exhibiting different molecular conformations, different patterns of intermolecular hydrogen bonding and different modes of supramolecular aggregation.

The biological potential of compounds of the tricyclic dibenzo[b,e]azepine system has resulted in considerable synthetic efforts to develop efficient methods for the synthesis of new derivatives of this kind. (9RS,15RS)-9-Ethyl-11-methyl-9,13b-dihydrodibenzo[c,f]thiazolo[3,2-a]azepin-3(2H)-one, C19H19NOS, (I), crystallizes as a kryptoracemate with Z' = 2 in the space group P21, with one molecule each of the (9R,15R) and (9S,15S) configurations in the asymmetric unit, while (9RS,15RS)-9-ethyl-7,12-dimethyl-9,13b-dihydrodibenzo[c,f]thiazolo[3,2-a]azepin-3(2H)-one, C20H21NOS, (II), crystallizes with Z' = 1 in the space group C2/c. Ethyl (13RS)-2-chloro-13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate, C22H20ClNO3, (III), exhibits enantiomeric disorder in the space group P-1 such that the reference site is occupied by the 13R and 13S enantiomers, with occupancies of 0.900 (6) and 0.100 (6). In each of the two independent molecules in (I), the five-membered ring adopts an envelope conformation, but the corresponding ring in (II) adopts a half-chair conformation, while the six-membered ring in the major form of (III) adopts a twist-boat conformation. The conformation of the seven-membered ring in each of (I), (II) and the major form of (III) approximates to the twist-boat form. The molecules of compound (I) are linked by two C-H...O hydrogen bonds to form two independent antiparallel C(5) chains, with each type containing only one enantiomer. These chains are linked into sheets by two C-H...π(arene) hydrogen bonds, in which the two donors are both provided by the (9R,15R) enantiomer and the two acceptor arene rings form part of a molecule of (9S,15S) configuration, precluding any additional crystallographic symmetry. The molecules of compound (II) are linked by inversion-related C-H...π(arene) hydrogen bonds to form isolated cyclic centrosymmetric dimers. The molecules of compound (III) are linked into cyclic centrosymmetric dimers by C-H...O hydrogen bonds and these dimers are linked into chains by a π-π stacking interaction. Comparisons are made with some related structures.