Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• experimental data as well as theoretical calculations suggested that both cycloadducts, 14 and 15, arise from the same intermediate, the cycloheptanyl metal–carbene species VIII, which might evolve through a 1,2-hydrogen shift to give the seven-membered carbocycles 14 (Scheme 8, a), or by a ring-contraction

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• the product without deuterium content (Scheme 2, reaction 2). The results of these labeling experiments reveal a 1,4-hydrogen shift [20][21][22] in the d1-1a→d1-4a transformation. Scheme 3 shows a plausible mechanism to rationalize the transformation of the allenyl acetal 1e into the observed

• alternative route involving the protonation of the fulvene intermediate D because this route would water as a proton source. The formation of the fulvene intermediate D from allyl cation B is assisted by a weak base like nitrone [18]. We envisage that a 1,2-hydrogen shift for the allyl cation B fails to

Aerobic radical multifunctionalization of alkenes using tert-butyl nitrite and water

• Daisuke Hirose and
• Tsuyoshi Taniguchi

Beilstein J. Org. Chem. 2013, 9, 1713–1717, doi:10.3762/bjoc.9.196

• 10.3762/bjoc.9.196 Abstract Water induces a change in the product of radical multifunctionalization reactions of aliphatic alkenes involving an sp3 C–H functionalization by an 1,5-hydrogen shift using tert-butyl nitrite and molecular oxygen. The reaction without water, reported previously, gives nitrated

• intramolecular radical hydrogen transfer reactions. An 1,5-hydrogen shift is the most favourable process [17], and useful methods such as the Barton reaction and the Hofmann–Löffler–Freytag reaction have been reported [18][19][20]. Recently, we reported a novel radical multifunctionalization reaction of

• the mutifunctionalized product 19 as a single isomer. The stereochemistry of 19 could be presumably assigned by considering the 1,5-hydrogen shift mechanism (entry 5) [17]. The reaction of alkene 10 bearing a methyl ester moiety gave γ-lactone 20 by intramolecular transesterification with a tertiary

The preparation of several 1,2,3,4,5-functionalized cyclopentane derivatives

• André S. Kelch,
• Peter G. Jones,
• Ina Dix and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 1705–1712, doi:10.3762/bjoc.9.195

• a ratio of 3:1, and in Le Goff´s hands it was as much as 15:1, we observed the formation of 24 as a minor product (24:25 = 1:8). One reason for this difference could be a pericyclic 1,5-hydrogen shift between the two valence isomers generating different ratios under different preparation and work-up

• conditions. Another equilibration mechanism could involve a base-induced 1,5-hydrogen shift. Since the mechanism of formation of 24 and 25 was not the main concern of our investigations, we did not clarify these points. The differentiation between the symmetrical 24 and the non-symmetrical 25 by 1H NMR

Cascade radical reaction of substrates with a carbon–carbon triple bond as a radical acceptor

• Hideto Miyabe,
• Ryuta Asada and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2013, 9, 1148–1155, doi:10.3762/bjoc.9.128

• addition–trapping process. Next, the reaction of propiolic acid derivative 8 was tested, because we expected the [1,5]-hydrogen shift from 1,3-dioxolane ring into the reactive vinyl radical as shown as D. However, the simple adduct 11 was only obtained in 78% yield. The results from these studies show that

Caryolene-forming carbocation rearrangements

• Quynh Nhu N. Nguyen and
• Dean J. Tantillo

Beilstein J. Org. Chem. 2013, 9, 323–331, doi:10.3762/bjoc.9.37

• structure: does the bridging hydrogen have hydride character (as expected for a structure resembling a transition-state structure for a 1,2-hydrogen shift) or proton character (as expected for a “proton sandwich”)? This issue was addressed through calculations of 1H chemical shifts, which predicted a

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

• indanones (Scheme 4) [59]. Phenylrhodation of 1g first proceeds to form 1A. A subsequent intramolecular 1,4-hydrogen shift gives 1B, which smoothly undergoes an intramolecular 1,4-addition to yield 1C. Finally, transmetalation from the phenylzinc reagent to rhodium enolate 1C affords zinc enolate 1h, which

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• symmetry conservation rules, studies of chiral substituted cycloheptatrienes showed a preference for the “forbidden” path with inversion of configuration [32][33][34][35]. Finally, a suprafacial [1,5]-hydrogen shift with an activation energy of approximately 31 kcal·mol−1 was unveiled by a high-temperature

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

• , followed by addition of the generated alkenyl metallic species to the α,β-unsaturated silyl oxonium moiety, to give a bicyclic carbene intermediate XVI [59]. These species, which do not incorporate an α-hydrogen atom that could participate in a 1,2-hydrogen shift process, evolve through a 1,2-alkyl

• ) catalyst is able to activate these allenic intermediates in situ, triggering a stepwise intramolecular (3 + 2) annulation reaction with the pendant alkene. This cycloaddition provides a cyclic gold carbene species XXV, which is eventually transformed into the final bicyclic adduct by a 1,2-hydrogen shift

• of the allene to afford a metal–allyl cation intermediate of type XXIX, which subsequently undergoes a concerted (4 + 3) cycloaddition reaction with the diene. The resulting metal carbene species (XXX) eventually evolves through a 1,2-hydrogen shift, leading to seven-membered carbocycles 50 and

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

• -gold(I) acetylide, followed by a 1,5-hydrogen shift (Scheme 44). A range of indole based cycloaddition products were obtained by concerting the initial regioselective site-selective indole attack (C3 position) to the C–C multiple bonds [132][133][134]. In the case of gold(I)-catalyzed reactions

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

• a tricyclo[3.1.0.02,6]hexane structure. Rearrangement of G by consecutive 1,2-alkyl shifts, proceeding through carbocations H and I and Dewar-type benzene J as intermediates, followed by ring-opening and a 1,2-hydrogen shift, ultimately led to 84a or 84b (Scheme 30) [26]. Since intermediates G–J are

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• -configuration. In addition, 6π-electron electrocyclic ring-closure could be carried out with 3-amido-trienes to afford cyclic 2-amido-dienes, and such electrocyclic ring-closure could be rendered in tandem with the 1,3-hydrogen shift. Keywords: allenamides; 2-amido-dienes; 3-amido-trienes; electrocyclic ring

• -closure; 1,3-hydrogen shift; isomerization; Introduction While allene isomerization to afford conjugated dienes is a well-known and thermodynamically favourable process, it is not trivial kinetically. A concerted allene isomerization leading to a diene involves a 1,3-hydrogen shift, which constitutes a

• ][64] (for examples see [65][66][67][68][69][70][71][72]), herein, we report details of an efficient entry to synthetically rare 2-amido-dienes [73][74][75][76][77] via a regio- and stereoselective 1,3-hydrogen shift of allenamides. Results and Discussion As part of our initial screening efforts, both

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

• Franca M. Cordero,
• Carolina Vurchio,
• Stefano Cicchi,
• Armin de Meijere and
• Alberto Brandi

Beilstein J. Org. Chem. 2011, 7, 298–303, doi:10.3762/bjoc.7.39

• the enantiopure nitrone 10 [42] derived from L-tartaric acid was complete within only 1.5 h at 120–125 °C under microwave (MW) heating and afforded the oxospirocyclopropanes anti-12 and syn-12 in 55% overall yield along with the 1,5-hydrogen shift product 13 (13%) (Scheme 3, see Supporting Information

• into 19 under the reaction conditions. However, in the absence of the catalyst, heating of diene 18 under otherwise identical conditions did not induce any isomerization of 18 to 19, which confirms that Rh also catalyzes the 1,5-hydrogen shift in 18. The structure assignment was easily made on the

• experimental data). Treatment of 6 (1.2–1.7 equiv) with BCP (2) in xylenes at 125 °C for 64 h directly afforded the α-oxocyclopropane derivative 8 [13] (51–72% yield) along with a minor amount of the open-chain isomer 9 (20–23% yield). The open-chain isomer 9 is derived from a rarely observed 1,5-hydrogen

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• ] hydrogen shift produced the conjugated 1,5-dipolar species 132 that subsequently underwent concerted disrotatory electrocyclisation of the 6π-electron system to give a mixture of the cis and trans isomers 133a and 133b (ratio 1.8:1). Compound 133b was separated by chromatography and a final dihydroxylation

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• ). Typically the thermal reversion of the open forms is very fast [17][18][19][20]. Quite recently, the formation of allene intermediates at low temperatures was also reported in the literature. They originate from open merocyanine isomers and are formed via a 1,5-hydrogen shift reaction [21][22]. However

Part 2. Mechanistic aspects of the reduction of S-alkyl- thionocarbonates in the presence of triethylborane and air

• Florent Allais,
• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 46, doi:10.1186/1860-5397-3-46

• substrate was chosen because of its low molecular weight and its simple structure that ensure easy spectral analyses (NMR, MS, GC-MS) and also because a putative 1,5-hydrogen shift between the intermediate radical and a hydrogen atom in the α-position to the ketone cannot intervene. This point was discussed

• at the end of the first part of this series.[3] On the other hand, we proved that a similar 1,5-hydrogen shift in which the acetyl group would be implicated does not occur either (see below). The standard experiment (entry 1) performed without any source of deuterium serves to evaluate the natural

• parent xanthate. This proves that no 1,5-hydrogen shift occurred. The replacement of chloroform-d by 1,2-dichloroethane gave similar results (85%, entry 3). More interestingly, the incorporation was still high when methanol-d4 was replaced by CH3OD (76%, entry 4). Methanol-d4 or CH3OD can be in turn

Part 1. Reduction of S-alkyl- thionocarbonates and related compounds in the presence of trialkylboranes/air

• Jean Boivin and
• Van Tai Nguyen

Beilstein J. Org. Chem. 2007, 3, No. 45, doi:10.1186/1860-5397-3-45

• donor (diethylphosphite) were used on the same type of substrate.[11] Of course the hypothesis of a putative 1,5-hydrogen shift that would operate to a minor extent is not fully ruled out, and should certainly deserve further experimentation. However, one should stress that the reduction with the system

2-Arylhydrazononitriles as building blocks in heterocyclic synthesis: A novel route to 2-substituted- 1,2,3-triazoles and 1,2,3-triazolo[4,5-b]pyridines

• Saleh M. Al-Mousawi and
• Moustafa Sh. Moustafa

Beilstein J. Org. Chem. 2007, 3, No. 12, doi:10.1186/1860-5397-3-12

• . [15] Compound 9 was coupled with benzenediazonium chloride most likely through the intermediate 11a. The latter intermediate cyclized into 11b. Deacetylation of 11b followed by hydrogen shift produced 10. This again confirms that the acetyl and the amino functions in cyclization product are adjacent