Gold catalyzed oxycyclizations of alkynols and alkyndiols

Alcaide, Benito; Almendros, Pedro; Alonso, José M.

doi:10.1039/c1ob05249g

Cited by 110 publications

(23 citation statements)

References 174 publications

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“…Thus, a crucial target for organic chemists is to find the appropriate reaction conditions, allowing functional group compatibility and providing high efficiency and atom economy. During the last years, gold-catalyzed cycloisomerization of alkynol-based systems has emerged as a useful tool in this area, allowing the synthesis of different structures such as furans, dihydrofurans, pyrans, furanones or ketals, among many other heterocyclic systems and naturally occurring structures [ 1 , 2 , 3 ].…”

Section: Introductionmentioning

confidence: 99%

Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

2011

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The last decade has witnessed dramatic growth in the number of reactions catalyzed by gold complexes because of their powerful soft Lewis acid nature. In particular, the gold-catalyzed activation of propargylic compounds has progressively emerged in recent years. Some of these gold-catalyzed reactions in alkynes have been optimized and show significant utility in organic synthesis. Thus, apart from significant methodology work, in the meantime gold-catalyzed cyclizations in alkynol derivatives have become an efficient tool in total synthesis. However, there is a lack of specific review articles covering the joined importance of both gold salts and alkynol-based compounds for the synthesis of natural products and derivatives. The aim of this Review is to survey the chemistry of alkynol derivatives under gold-catalyzed cyclization conditions and its utility in total synthesis, concentrating on the advances that have been made in the last decade, and in particular in the last quinquennium.

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Section: Introductionmentioning

confidence: 99%

Gold-Catalyzed Cyclizations of Alkynol-Based Compounds: Synthesis of Natural Products and Derivatives

2011

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“…Our research group previously reported the catalytic cascade isomerization reactions of allyl propargyl ethers to allenic aldehydes and dienals, in whicht he olefin isomerization,t he propargyl Claisen rearrangement, and the carbonyl migration reactions are catalyzed through both s-a nd p-bond activation with as ingle cationic rhodium(I) complex. [17] Therefore, we en-visioned that the cationic rhodium(I) complex would catalyze oxycyclization [18,19] through p-bond activation as well as 1,2-silicon and 1,3-carbon (alkyne)m igrations of bis(2-ethynylphenol)silane 1,w hich would be readily prepared from commercially available dichlorodiisopropylsilane, to benzofuranylmethylidene-benzoxasilole 2 (Scheme 1, bottom).…”

Section: Resultsmentioning

confidence: 99%

Rhodium‐Catalyzed Cascade Synthesis of Benzofuranylmethylidene‐Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid‐State Fluorescence

Namba

Hayashi

Kawauchi

et al. 2018

Chemistry A European J

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A new synthetic route to highly fluorescent benzofuranylmethylidenebenzoxasiloles through cationic rhodium(I)/binap complex-catalyzed cascade cycloisomerization of bis(2-ethynylphenol)silanes has been developed involving 1,2-silicon and 1,3-carbon (alkyne) migrations followed by oxycyclization. The present synthesis requires only three steps, starting from commercially available dichlorodiisopropylsilane, which is markedly shorter than our previous synthesis (eight steps starting from commercially available chlorodiisopropylsilane). Theoretical calculations elucidated the mechanism of the above cascade cycloisomerization. This reaction is initiated by the formation of a rhodium vinylidene not through direct 1,2-silicon migration but rather through an unprecedented stepwise 1,5-silicon migration followed by C-Si bond-forming cyclization from a dearomatized allenylrhodium complex. Subsequent 1,3-carbon (alkyne) migration leading to a η -allenyl/propargyl-rhodium complex followed by oxycyclization through π-bond (alkyne) activation with the cationic rhodium(I) complex affords the benzofuranylmethylidenebenzoxasilole product. The structure-fluorescence property relationships of the thus obtained benzofuranylmethylidenebenzoxasiloles were investigated, which revealed that good fluorescence quantum yields were generated in the solution state (φ =69-87 %) by introduction of electron-donating alkyl and phenyl groups on two phenoxy groups. In the powder state, 4-methyl- and 4-methoxy-phenoxy derivatives exhibited efficient blue fluorescence (φ =52 % and 46 %, respectively). Especially, the 4-methylphenoxy derivative was thermally stable, and exhibited strong narrow-band fluorescence in the film state (blue, φ =95 %) and redshifted strong narrow-band fluorescence (green, φ =90 %) in the crystalline state as a result of the formation of an offset π-stacked dimer; the latter was confirmed by X-ray crystallographic analysis and by theoretical calculations.

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“…The TBAF deprotection of 55 proceeded without incident (93%; Scheme 9) enabling us to investigate the synthesis of the [6,6]-spiroketal 57 ( Table 2). We were satisfied to find AuCl with PPTS, standard cycloisomerization conditions, 17,18 gave the desired spiroketal in 27% yield (entry 1). 19 While investigating alternative conditions, we found simply mixing AuCl with diol 56 in DCM gave 57 in a much greater yield (66%; entry 2).…”

Section: Syn Thesismentioning

confidence: 99%