18887-53-1Relevant articles and documents
Preparation of benzannulated spiroketals by gold(III) catalyzed spirocyclization of alkynyl diols
Jónsson, Helgi Freyr,Fiksdahl, Anne
, p. 338 - 352 (2021/02/12)
The first gold(III)-oxazoline catalysed intramolecular tandem dihydroalkoxylations of alkynyl diols to give benzannulated 5,6-spiroketal products is reported. The results showed that Au(III)-bisoxazoline (BOX) and Au(III)-pyridine-oxazoline complexes are highly efficient catalysts for such spirocyclizations. The mono- and dibenzannulated 5,6-spiroketals were obtained in high yields (> 90 %) by rapid conversion of symmetrical and nonsymmetrical alkynyl diols, respectively. The Au(III)-BOX-BF4 catalyst generated minor spirocyclization enantioselectivity (up to 6 % ee). The choice of solvent was important for the outcome of the reactions.
Gold(I)-catalyzed cycloisomerizations and alkoxycyclizations of ortho-(alkynyl)styrenes
Sanjun, Ana M.,Rashid, Muhammad A.,Garca-Garca, Patricia,Martnez-Cuezva, Alberto,Fernndez-Rodrguez, Manuel A.,Rodrguez, Flix,Sanz, Roberto
supporting information, p. 3042 - 3052 (2015/02/05)
Indenes and related polycyclic structures have been efficiently synthesized by gold(I)-catalyzed cycloisomerizations of appropriate ortho-(alkynyl)styrenes. Disubstitution at the terminal position of the olefin was demonstrated to be essential to obtain products originating from a formal 5-endo-dig cyclization. Interestingly, a complete switch in the selectivity of the cyclization of o-(alkynyl)-a-methylstyrenes from 6-endo to 5-endo was observed by adding an alcohol to the reaction media. This allowed the synthesis of interesting indenes bearing an all-carbon quaternary center at C1. Moreover, dihydrobenzo[a]fluorenes can be obtained from substrates bearing a secondary alkyl group at the β-position of the styrene moiety by a tandem cycloisomerization/1,2-hydride migration process. In addition, diverse polycyclic compounds were obtained by an intramolecular gold-catalyzed alkoxycyclization of o-(alkynyl)styrenes bearing a nucleophile in their structure. Finally, the use of a chiral gold complex allowed access to elusive chiral 1H-indenes in good enantioselectivities.
An Unusual Example of a 6-Endo-Dig Addition to an Unactivated Carbon-Carbon Triple Bond
Padwa, Albert,Krumpe, Keith E.,Weingarten, M. David
, p. 5595 - 5603 (2007/10/03)
Methyl 2-ethynyl>benzoate was prepared as an intermediate for subsequent conversion to an α-diazo ketone.Under the basic conditions used to hydrolyze the methyl ester, the neighboring hydroxyl functionality underwent reaction with the unactivated acetylenic group, producing a benzopyranyl-substituted α-diazoacetophenone.Treatment of this diazocarbonyl compound with a catalytic quantity of rhodium(II) mandelate afforded a novel dibenzocyclononenone derivative.The reaction proceeds via an initially formed oxonium ylide which rearranges further by means of a 1,2-alkyl shift.A prime factor in determining the direction of internal cyclization to the triple bond is the presence of the carbomethoxy group in the ortho position of the β-phenyl ring.Thus, in contrast with related systems which exhibit a clear preference for 5-exo-dig cyclization at the acetylenic center, the 6-endo-dig addition is the preferred pathway for the o-formyl- and o-carbomethoxy-substituted alkynyl alcohols.Careful monitoring of the reaction actually showed that the reaction proceeds by initial formation of the 5-exo-dig product followed by a novel rearrangement to the 6-endo product.
