Microwave‐Assisted Dibromoolefination of Aromatic and Heteroaromatic Aldehydes and Ketones

Abstract

Microwave (MW) irradiation was successfully employed to convert aromatic and heteroaromatic aldehydes and ketones efficiently to the corresponding dibromoolefins. Exemplified by the successful dibromoolefination of traditionally inert pyridyl‐flanked carbonyls, MW activation significantly broadens the scope of this valuable transformation, although some limitations especially with electron‐rich aromatic ketone derivatives remain.

Cross‐Conjugated π‐Scaffolding with Pendant N‐Heterocyclic Metal‐Binding Sites

“…The data were referenced against Fc + /Fc (Fc = ferrocene) and are summarised in Table 2. [22] The reduction of di(2-pyridyl) ketone shows a cathodic shift of almost 350 mV in comparison with that of 4,5-diazafluoren-9-one (Table 2). 400 mV compared with that of 2a.…”

“…The spectral differences between pyridyl-based compound 1 (blue trace in Figure 2) and the diazafluorenylidene systems 2a and 2b (Figure 2, black and red traces, respectively) are quite striking. The extended and cross-conjugated delocalisation paths in 1, 2a and 2b become further apparent from a comparison of their longest wavelength absorptions with those of the corresponding ketones that served as the starting materials [22] for 4 and 5 (not shown). Clearly, extended π-electron delocalisation is feasible and more pronounced in the diazafluorenylidene compounds 2a and 2b and results in bathochromically shifted absorptions.…”

“…[22] A systematic evaluation of different reaction conditions for the dialkynylation led us to use tetrakis(triphenylphosphine)palladium(0) and copper(I) iodide in toluene together with diisopropylamine (DIPA) as a base. The dibromoolefins 4 and 5, which serve as starting materials for the one-step preparations of 1 and 2, were obtained by a newly developed microwaveassisted dibromoolefination of the corresponding ketones with CBr 4 and PPh 3 .…”

“…Compound 4 [22] (300 mg, 0.90 mmol) was dissolved in toluene (20 mL). Pd(PPh 3 ) 4 (30 mg, 3 mol-%), diisopropylamine (1 mL), triisopropylsilylacetylene (0.9 mL, 4.4 mmol) and CuI (8 mg, 5 mol-%) were added to the solution, and the mixture was stirred overnight at 90°C.…”

“…The dibromoolefins 4 and 5, which serve as starting materials for the one-step preparations of 1 and 2, were obtained by a newly developed microwaveassisted dibromoolefination of the corresponding ketones with CBr 4 and PPh 3 . [22] A systematic evaluation of different reaction conditions for the dialkynylation led us to use tetrakis(triphenylphosphine)palladium(0) and copper(I) iodide in toluene together with diisopropylamine (DIPA) as a base. Both solvents allow a reaction temperature above 60°C, which is crucial for obtaining the desired compounds in satisfactory yields.…”