Expedient Synthesis of Functionalized Conjugated Enynes: Palladium‐Catalyzed Bromoalkynylation of Alkynes

Abstract

Von der gleichen Seite: Die direkte cis‐Addition von Bromalkinen 1 an Alkine 2 in Gegenwart eines Palladium(II)‐Katalysators ergibt difunktionalisierte Enine 3 als Produkte. Die Methode bietet einen einfachen Zugang zu Bromalkeninen. Ein ungewöhnlicher Reaktionsmechanismus wird vorgeschlagen.

Palladium‐Catalyzed Bromoalkynylation of CC Double Bonds: Ring‐Structure‐Dependent Synthesis of 7‐Alkynyl Norbornanes and Cyclobutenyl Halides

“…[4] Thus, we decided to react phenylethynyl bromide (2 a) with norbornene (1 a), expecting to obtain 2-bromo-3-(2-phenylethynyl)bicyclo[2.2.1]heptane (3 aa; Scheme 1). However, when using the previously optimized conditions, [2] we did not detect the formation of 3 aa, instead we obtained 2-bromo-7-(2-phenylethynyl)-bicyclo[2.2.1]heptane (3 a) in excellent yield, as confirmed by 1 H NMR spectroscopy. This unexpected result attracted our interest, since, to the best of our knowledge, no example of a direct 7-alkynyl bromonorbornane formation has been reported.…”

“…[1] We previously achieved highly regio-and stereoselective bromoalkynylation of internal alkynes for the synthesis of conjugated cis-bromoalkenynes. [2] Subsequent research on this subject revealed a further use of bromoalkynes in complex molecule synthesis.…”

Palladium‐Catalyzed Tandem N‐Vinylation and Cyclization of Anilines and Haloenynes: An Efficient Approach to Substituted Quinolines

“…We next tested the reaction in the presence of different catalysts. PdA C H T U N G T R E N N U N G (PPh 3 ) 2 Cl 2 , was superior to any other palladium catalysts so far tested (entries 5,[10][11][12][13][14][15][16][17]. Notably, the reaction was not effective when only PdA C H T U N G T R E N N U N G (OAc) 2 or PdA C H T U N G T R E N N U N G (CH 3 CN) 2 Cl 2 was employed (entries 10 and 11).…”

“…metaChloroaniline 2i afforded the para-cyclization regioisomer 4i and ortho-cyclization isomer 5i in 30% and 27% yields (entry 9). On the other hand, different combinations of substituents on the alkyne and alkene of bromoenynes can be used to allow the synthesis of alkyl-and arylsubstituted quinolines (entries [10][11][12][13]. When alkyl substituents were on the end of alkyne, the desired product could not be observed.…”

“…Interesting observations emerged from the data in Table 1. We first tried the reaction of 2a (1.1 mmol) with bromoenyne 3a (1.0 mmol), which was readily prepared by the direct bromoalkynylation of 3-hexyne, [10] 5 mol% of PdA C H T U N G T R E N N U N G (PPh 3 ) 2 Cl 2 , and 2.0 equivalents of t-BuONa in 2.0 mL of NMP at 90 8C for 24 h. The desired product 4a was not observed (entry 1). The screening of various solvents revealed that the solvent played an important role in this reaction (entries 1-4).…”