Pd-Catalyzed Tandem Isomerization/Cyclization for the Synthesis of Aromatic Oxazaheterocycles and Pyrido[3,4-b]indoles

Abstract

An effient tandem process consisting of palladium-catalyzed double-bond isomerization of long-chain olefins and subsequent intramolecular cyclization promoted by B2(OH)2 for the synthesis of aromatic oxazaheterocycles is disclosed. This strategy can also provide rapid access to pyrido­[3,4-b]­indoles, trans-2-olefins, and eneamides bearing various functional groups with high regio- and stereoselectivity.

Functionalization of Biphenylcarbazole (CBP) with Siloxane-Hybrid Chains for Solvent-Free Liquid Materials

“…Then, we envisaged incorporating the allyl linker using Stille coupling, given the known versatility and stability of tin reagents [ 55 , 56 ]. Catalytic conditions on 3-bromocarbazole 2 were used to dodge side Pd-catalyzed reactions such as homocoupling, reductive dehalogenation, Buchwald–Hartwig amination, and isomerization of the allyl substituent [ 21 , 22 , 44 , 45 , 46 , 47 , 48 ]. Trials were performed on a small scale (50.0 mg, 0.203 mmol) and characterized by GC/MS conversions as shown in Table 1 .…”

“…Isolation of the product with purity above 99% could only be achieved by repetitive column chromatography with silica/sample ratio greater than 400/1 while monitoring by GC/MS and not by thin layer chromatography. It seems that the extended conjugation on this aromatic moiety bearing a (polarizable) heteroatom (N-H) increases the electrostatic interactions among the molecules rendering the separation process highly complicated [ 46 , 48 , 59 ].…”

“…However, the addition of alkenyl linkers for introducing siloxane chains to these conjugated cores, particularly those activated with heteroatoms such as carbazoles brings elevated complexity due to unfavored side reactions [ 21 , 22 ]. Among them, metal-catalyzed polymerization and isomerization were well documented in such aromatic systems in the literature [ 44 , 45 , 46 , 47 , 48 ]. Herein, we present a synthetic methodology to obtain CBP molecules functionalized by siloxane chains using a short ω-alkenyl (essentially allyl) linker.…”

Gold(I)-Catalyzed Synthesis of 4H-Benzo[d][1,3]oxazines and Biological Evaluation of Activity in Breast Cancer Cells

“…Some of the more representatives include metal-catalyzed procedures with Pd, − Cu, and Fe; also, different metal-free-catalyzed protocols using I 2 , or chiral phosphoric acids have been reported. All the aforementioned methods involve the use of high temperatures, potentially toxic reagents or starting materials, and general nonmild conditions.…”

Simple Tandem Olefin Isomerization/Intramolecular Hydroamination of Alkenyl Amines with Various Allylic Tethers

“…The olefin moiety of allyl ethers and amines can provide the starting point for tandem annulations triggered by initial olefin isomerization to construct various heterocycles. Since the pioneering work by the Terada group, several research groups have explored a variety of a complex TM hydride (TM-H)/Brønsted acid-cocatalyzed tandem olefin isomerization/intramolecular hydroalkoxylations of allyl ethers and amines containing a tethered O-nucleophile to afford O , O - and O , N -acetals, respectively (Scheme a) . A related BF 3 ·Et 2 O-mediated reaction of allyl amines with a tethered thiol involving hydrothioalkoxylation was also reported, albeit with a very limited scope .…”