Bicyclic Amidines as Reagents in Organic Syntheses

Bis- and tris(amidine)fluoroboron cations and mixed tetrahaloborate anions: NMR studies of mixed boron trihalide adduct redistribution reactions involving amidines as strong nitrogen bases

“…However, these observations are accounted for if the amidine.H+ cations and the chlorofluoroborate anions are both formed through reaction of amidine with the chloroform solvent. Strong bases can attack chloroform with the generation of carbenes (44): [9] Alternatively, reaction [9] might continue under excess amidine conditions, but the chlorofluoroborate anions would undergo chloride displacement by amidine (eq. [3]) so that their concentrations would not build up.…”

“…To avoid problems of N-H proton transfer, we have limited our work to N,N,N1-trialkyl-substituted amidines. Following preliminary studies with N,N,N1-trimethylacetamidine (Me2N-CMe=NMe) and N,N.N1-trimethylbenzamidine, which are not commercially available, our work on amidine interactions with mixed boron trihalide adducts has involved 1,8-diazabicyclo [ well established as strongly basic yet non-nucleophilic reagents in organic synthesis (9,10). DBN is one of the strongest amidine bases, with a pKb of about 0.5 in 50% aqueous ethanol (1 1).…”

Acyl cyanides as carbonyl heterodienophiles: application to the synthesis of naphthols, isoquinolones, and isocoumarins

“…, that the isocoumarins should be accessible by base-catalyzed elimination of HCN. Initial attempts employing DBU or DBN, known to catalyze efficient dehydrohalogenation (15), gave unsatisfactory results with 8a-e. Potassium tert-butoxide proved to be the reagent of choice as treatment of an icecooled THF solution of compound 8a (Scheme 8) with 1.5 equivalents of the base yielded the known isocoumarin 12a (16) in 50% yield. Similarly, isocoumarin 12b (17) was prepared from 8e in 66% yield.…”

Utilization of the Sterically Hindered Base, 4-Hydroxy-2,2,6,6-tetramethylpiperidine, as a Hydrogen Halide Acceptor

“…Dehydrohalogenation of Alkyl Bromides [8] Recently, considerable interest has been shown in the utilization of sterically hindered bases in the synthesis of alkenes via the corresponding alkyl halides [1,2,5,6,20]. The bicyclic bases, 1,5-diazabicyclo[4,3,0]non-5-ene (DBN) and 1,8-diazabicyclo(5,4,0)undec-7-ene (DBU) [21,22] initially became known as dehydrohalogenating agents, i. e., hydrogen halide acceptors, in the syntheses of [20]. In view of the utility of 4-hydroxy-2,2,6,6-tetramethylpiperidine (1) as a hydrogen halide acceptor in the exhaustive methylation reaction of primary amines, we attempted to apply 1 also as a dehydrohalogenating agent for the conversion of alkyl halides to alkenes.…”