Some epoxy-acetylene cyclisations

s-Block cooperative catalysis: alkali metal magnesiate-catalysed cyclisation of alkynols

“…This product differs from the product previously reported using heavier alkaline earth 59,60,80 or lanthanide amides. 38,57,58 With these catalytic systems the non-aromatic product, 3-methyl-2methylene-2,5-dihydrofuran, is observed, and it is only when we move to a transition metal catalyst, 44 we see formation of the aromatic furan product.…”

“…[53][54][55][56] However more commonly, where no electronically biased intermediate is formed, exocyclisation occurs due to the more favourable approach of the nucleophile with respect to the p-system. 57,58 Besides the numerous examples of transition metal catalysts, the use of f-and s-block catalysts for this reaction has been investigated. In terms of f-block chemistry, Marks has utilised lanthanide amide catalysts, 59,60 while Otero and Lara-Sánchez have employed heteroscorpionate rare earth catalysts.…”

An Unusual Example of a 6-Endo-Dig Addition to an Unactivated Carbon-Carbon Triple Bond

“…However, subsequent experimental work suggested that, in the case of electronically unbiased acetylenes, exo-dig cyclizations are actually favored. 34 For example, Bailey and co-workers have shown that 5-alkyn-1 -yllithiums undergo anionic cyclization via a highly regiospecific 5-exo-dig process involving stereoselective syn addition to the triple bond.35 It has also been observed that both exo and endo pathways can occur during the base-induced reaction of l-(2-hydroxyphenyl)-3-arylprop-2-yn-l-ones (24).36,37 Cyclization of ynone systems of type 24 is reported to give varying amounts of the corresponding flavones 25 and aurones 26, depending on the substituent groups (X) and the reaction conditions. The observations made with this system strongly suggest that cyclization occurs via the respective vinyl carbanions.…”

“…Benzofuran 40 was acidified with a saturated ammonium chloride solution and immediately extracted with CH2CI2. The combined CH2CI2 extracts were concentrated under reduced pressure to give 2-(177-2-benzopyran-3-yl)benzaldehyde (34) which showed singlets at 5.50 (2H), 7.12 (1H), and 10.24 (1H) in the -NMR. Benzopyran 34 was further treated with an ammonium chloride solution and extracted with CH2CI2, and the solvent was removed under reduced pressure.…”