Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• the 1,6-enyne 194a producing 196 which undergoes an oxidative cyclization leading to 197. Subsequent β-hydride elimination forms 198 which side-on coordinates with azabenzonorbornadiene 30c forming 199. Migratory insertion of the olefin followed by reductive elimination of the hydride affords the

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• the 1,6-enyne 35 followed by reductive elimination of the carbon nucleophile 38. Interestingly, this reaction proceeds via the cleavage of heteroelements and activated C–C bonds prior to reductive elimination of the metallacyclic ate-complex, resulting in the net formation of two new C–C bonds

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• )2-catalyzed hydroxylative carbocyclization of 1,6-enyne 156 (Scheme 45) [104]. It was observed that from 1,7-enynes, six-membered rings were formed in low to moderate yield while from 1,8-enynes, uncyclized hydrated products were isolated. as major products along with different byproducts. In a Hg

• acids and alcohol to furan, pyran, and spirocyclic derivatives. Hg(II)-salt-mediated cyclization of 1,4-dihydroxy-5-alkyne derivatives. Six-membered morpholine derivative formation by catalytic Hg(II)-salt-induced cyclization. Hg(OTf)2-catalyzed hydroxylative carbocyclization of 1,6-enyne. a) Hg(OTf)2

• -catalyzed hydroxylative carbocyclization of 1,6-enyne. b) Proposed mechanism. a) Synthesis of carbocyclic derivatives using a catalytic amount of Hg(II) salt. b) Proposed mechanism for dihydronapthanene formation. Cyclization of 1-alkyn-5-ones to 2-methylfuran derivatives. Hg(NO3)2-catalyzed synthesis of 2

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• presence of fluorinated groups on the alkenyl moiety of the 1,6-enyne resulted in low yields (lower than 35%) of the corresponding cyclized products, due to the poor reactivity of the fluorinated olefin (Scheme 6). For example, difluoroalkene-containing compound 1 decomposed and no cyclized product was

• trifluoromethyl-substituted allylic alcohols 4 and 5 afforded the corresponding cyclized products 9 and 10 (31% and 34% yield, respectively) as inseparable mixtures of diastereoisomers. Finally, 1,6-enyne 6, bearing a 4-fluorophenyl group on the olefin, stereoselectively produced trans-oriented arylcyclopentenone

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• reaction to achieve spirocyclic pyrrolocyclopentenone derivatives. Specifically, the KA2 reaction was envisaged taking into account cyclic ketones, to install a quaternary carbon atom carrying the required 1,6-enyne moiety for the subsequent Pauson–Khand reaction, thus achieving the corresponding tricylic

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• through ring-expanding cyclopentane annulations based on a Prins–pinacol rearrangement [17][18] and Au(I)-catalyzed pinacol-terminated 1,6-enyne cyclizations [19][20], the C3a–C7a bond formation occurring in the last step of both procedures. Finally, Snyder gained access to the type A hydrindane nucleus

Chiral cyclopentadienylruthenium sulfoxide catalysts for asymmetric redox bicycloisomerization

• Barry M. Trost,
• Michael C. Ryan and
• Meera Rao

Beilstein J. Org. Chem. 2016, 12, 1136–1152, doi:10.3762/bjoc.12.110

• alcohols revealed a matched/mismatched effect that was strongly dependent on the nature of the solvent. Keywords: asymmetric catalysis; [3.1.0] bicycles; [4.1.0] bicycles; cycloisomerization; 1,6-enyne; 1,7-enyne; ruthenium catalysis; sulfoxide; Introduction Due to their prevalence in natural products [1

• more broadly accessible to our synthetic method (Table 6). While the 1,6-enyne substrates 36 and 38 exhibited the desired reactivity in THF, the enantioselectivities for the process were poor. Considering how impactful a judicious choice of solvent had on the enantioselectivity of the [4.1.0] bicycles

• determining enantioselectivity? To answer these questions, we synthesized a 1,6-enyne containing an enantioenriched propargyl alcohol using our group’s zinc ProPhenol chemistry (Scheme 7). By employing the opposite enantiomers of the ProPhenol catalyst, either enantiomer of propargyl alcohol can be accessed

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• schisanwilsonene A (126, see Scheme 15), isolated from Schisandra wilsoniana [111], a plant used in traditional chinese medicine. Submission of 1,6-enyne 116 to cationic gold-catalyst 117 led to 5-exo-dig cyclization and intermediate formation of bridged bicycle 119. Subsequent 1,5-acyl-shift afforded

Gold(I)-catalyzed 6-endo hydroxycyclization of 7-substituted-1,6-enynes

• Ana M. Sanjuán,
• Alberto Martínez,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2013, 9, 2242–2249, doi:10.3762/bjoc.9.263

• aromatic ring or an alkenyl group at the C7-position of the 1,6-enyne the cyclization results almost completely selective via the 6-endo mode (Table 2, entries 2,3 and entries 6,7). However, in the case of halogen-containing aromatic substituents at C7 the formation of the corresponding products 3 or 8

Recent advances in transition-metal-catalyzed intermolecular carbomagnesiation and carbozincation

• Kei Murakami and
• Hideki Yorimitsu

Beilstein J. Org. Chem. 2013, 9, 278–302, doi:10.3762/bjoc.9.34

• reagents (Scheme 54) [147]. They assumed that the active species were organocuprates and that the radical character of carbocupration enabled bulky sec- or tert-alkylmagnesium reagents to be employed. Chromium-catalyzed carbomagnesiation of 1,6-diyne (Scheme 55) [148] and 1,6-enyne (Scheme 56) [149] also

• methallylmagnesium reagent would give 5l efficiently. The reaction of 1,6-enyne also proceeded through a tetraallylchromate complex as an active species (Scheme 56). However, the second cyclization did not take place. Conclusion We have summarized the progress in transition-metal-catalyzed carbomagnesiation and

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• , the group of Echavarren has recently developed a formal (2 + 2 + 2) gold-catalyzed synthesis of interesting oxa-bridged bicyclo[5.3.0]decanes from 1,6-enyne precursors equipped with an appropriately tethered carbonyl group (27, Scheme 16) [66]. In these processes, the carbonyl acts as a nucleophile

Asymmetric Au-catalyzed cycloisomerization of 1,6-enynes: An entry to bicyclo[4.1.0]heptene

• Alexandre Pradal,
• Chung-Meng Chao,
• Patrick Y. Toullec and
• Véronique Michelet

Beilstein J. Org. Chem. 2011, 7, 1021–1029, doi:10.3762/bjoc.7.116

• [53][54][55], we selected 4-MeO-3,5-(t-Bu)2-MeOBIPHEP-(AuCl)2 complex [56][57][58] as the best candidate for such a transformation. Initial experiments were performed using N-tosyl allyl substrate 1a and oxygen-linked propargylic 1,6-enyne 2a as model substrates (Table 1). The reaction of 1a was

• presence of diversely functionalized aryl iodides (Scheme 2). The corresponding substituted alkynes 2b–e [46] were isolated in 71–85% yield. An analogous 1,6-enyne 6 [64] was also reacted with 3-bromoiodobenzene under the same reaction conditions and led to the formation of substrate 2f in 58% isolated

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• , gold-catalyzed domino processes with 1,6-enynes have been shown to proceed in high yields to provide access to carbon skeletons that are not easily synthesized by other approaches. A striking example of the latter is outlined in Scheme 19 [115]. The 1,6-enyne 68 reacts with substituted styrene 69 in

Au(I)/Au(III)-catalyzed Sonogashira-type reactions of functionalized terminal alkynes with arylboronic acids under mild conditions

• Deyun Qian and
• Junliang Zhang

Beilstein J. Org. Chem. 2011, 7, 808–812, doi:10.3762/bjoc.7.92

• hand, the more electron-rich 4-methoxyphenylboronic acid produced the lowest yield, likely due to a competing oxidation of the boronic acid by Selectfluor® [27][30]. Gratifyingly, a number of potentially reactive functionalities, such as tertiary amine, 4-methylbenzenesulfonate, 1,6-enyne and 1,6-diyne

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• already summarized in section 1 of this review, can offer further synthetic potential in combination with 1,6-enyne substrates. Echavarren successfully developed a gold-catalyzed Prins cyclization of enynes 70 to afford trans- and cis-octahydrocyclobuta[a]pentalene skeletons 71 and 72, respectively

A racemic formal total synthesis of clavukerin A using gold(I)-catalyzed cycloisomerization of 3-methoxy-1,6-enynes as the key strategy

• Jae Youp Cheong and
• Young Ho Rhee

Beilstein J. Org. Chem. 2011, 7, 740–743, doi:10.3762/bjoc.7.84

• -catalyzed cycloisomerization of a 3-methoxy-1,6-enyne 5 as the key strategy followed by Rh-catalyzed stereoselective hydrogenation of the cycloheptenone 4. Keywords: clavukerin A; cycloisomerization; gold catalyst; hydrogenation; stereoselectivity; Findings Clavukerin A is a member of marine trinorguaiane

• followed by several other racemic and enantioselective syntheses [2][3][4][5][6][7][8][9][10][11][12][13][14]. Herein, we report a short formal total synthesis of racemic clavukerin A employing the gold(I)-catalyzed cycloisomerization of a 3-methoxy-1,6-enyne as the key strategy, which was recently

• spectrum of the crude reaction product. Subsequent methylation gave the 1,6-enyne 5 in 88% yield. We then investigated the gold-catalyzed cycloisomerization of enyne 5 using the optimized conditions from our previous study [15]. The use of the pre-generated complex Au[P(C6F5)3]+SbF6− (2 mol %) provided the

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• ]. Wang et al. also examined the behaviour of other cyclopropen-1,n-ynes. For substrates 89a and 89b possessing a 1,6-enyne moiety, the gold-catalyzed cycloisomerization led to the tricyclic hydrocarbons 90a (80%) and 90b (74%), respectively. The alkyne, chemoselectively activated by the gold complex