ABSTRACT
Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the 'ITent' ('Tent' for 'tentacular') family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated.
ABSTRACT
A straightforward and scalable eight-step synthesis of new N-heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2-nitro-m-xylene. This process allows for the preparation of a novel class of NHCs coined ITent ("Tent" for "tentacular") of which the well-known IMes (N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (N,N'-bis(2,6-di(2-propyl)phenyl)imidazol-2-ylidene) and IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N'-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene), IHept (N,N'-bis(2,6-di(4-heptyl)phenyl)imidazol-2-ylidene) and INon (N,N'-bis(2,6-di(5-nonyl)phenyl)imidazol-2-ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-couplings was investigated.
ABSTRACT
A straightforward synthesis of the enantioenriched C8-C16 south part of (+)-13-deoxytedanolide has been reported. The strength of this approach relies on the preparation of similar functionalized fragments via the transformation of a unique dihydrofuran building block through a 1,2-metallate rearrangement.
Subject(s)
Macrolides/chemical synthesis , Macrolides/chemistry , Molecular Conformation , StereoisomerismABSTRACT
The total synthesis of the proposed structure for the minor myxobacterial metabolite 8-deshydroxyajudazol A (3) is described. The isochromanone moiety present in the eastern fragment was constructed by an intramolecular-Diels-Alder (IMDA). Difficulties were encountered with the formation of the 2,4-disubstituted oxazole, so this was synthesized via a modified approach. This involved selective acylation of the diol 7 with acid 8, azide displacement of the secondary alcohol, and subsequent azide reduction in the presence of base which induced an O,N shift to give the hydroxyamide 23. Cyclodehydration then gave the desired oxazole 24 and deprotection followed by mesylation and elimination produced the C15 alkene 5. Sonogashira coupling with the eastern fragment vinyl iodide 6 and partial reduction yielded 8-deshydroxyajudazol A (3).
Subject(s)
Azides/chemistry , Chromones/chemical synthesis , Oxazoles/chemical synthesis , Chromones/chemistry , Molecular StructureABSTRACT
The total synthesis of a stereoisomer of 8-deshydroxyajudazol B (4), the putative biosynthetic intermediate of the ajudazols A (1) and B (2), is described. The key steps in the synthesis included an intramolecular Diels-Alder (IMDA) reaction to secure the isochromanone fragment, a novel selective acylation/O,N-shift to give a hydroxyamide which was cyclized to the oxazole and a high yielding Sonogashira coupling to form the C18-C19 bond. Partial alkyne reduction then afforded the target 4.
Subject(s)
Coumarins/chemical synthesis , Alkynes/chemistry , Molecular Structure , Oxazoles/chemical synthesis , Oxidation-ReductionABSTRACT
The convergent synthesis of N-Boc-(2R,3R,8R,9R,4E,6E)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldecadenoic acid (enantio-N-Boc-ADDA) is reported. Our flexible approach takes advantage of highly efficient non-aldol aldol and cross-metathesis methodologies.
