Triple-channel microreactor for biphasic gas–liquid reactions: Photosensitized oxygenations

• Ram Awatar Maurya,
• Chan Pil Park and
• Dong-Pyo Kim

Beilstein J. Org. Chem. 2011, 7, 1158–1163, doi:10.3762/bjoc.7.134

• sensitizer. The results from the triple-channel microreactor and the batch reaction presented in Table 3 clearly indicate the efficiency of the former. Photosensitized oxygenation of α-terpinene The photosensitized oxygenation of α-terpinene is a Diels–Alder type [4 + 2] cycloaddition reaction. The product

A practical microreactor for electrochemistry in flow

• Kevin Watts,
• William Gattrell and
• Thomas Wirth

Beilstein J. Org. Chem. 2011, 7, 1108–1114, doi:10.3762/bjoc.7.127

• the product selectivity. Cycloadditions using the N-acyliminium ions as heterodienes with a variety of dienophiles, such as alkenes and alkynes, give the corresponding [4 + 2] cycloaddition products in high yields [10]. The same authors also reported a successful polymer synthesis using the same

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

• type 1 and alkynes (Scheme 1) [24][25]. The mechanism proposed by the authors involves an initial 5-endo nucleophilic attack of the carbonyl moiety on the metal–alkyne complex to generate a carbonyl ylide intermediate I, which undergoes a regioselective (4 + 2) cycloaddition with the external alkyne. A

• aforementioned mechanistic pathway [26]. According to the theoretical data, the formal (4 + 2) cycloaddition would indeed comprise a two-step process consisting of a dipolar (3 + 2) cycloaddition of the carbonyl ylide I to afford a carbene species III [27][28], followed by a 1,2-alkyl migration to yield the

• highly stereoselective (4 + 2) cycloaddition with the vinyl ether to yield, after the elimination of the gold catalyst, highly substituted oxacyclic systems 7 in good yields and with notable diastereoselectivities. Importantly, this reaction tolerates a wide range of vinyl ethers, and different

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

• a highly enantioselective three-component (393–395) cascade reaction which involved an enantioselective [4 + 2] cycloaddition reaction catalyzed by a chiral phosphoric acid and a subsequent catalytic intramolecular hydroamination by a gold(I) complex (Scheme 64) [180]. Further studies revealed that

• + 2] cycloaddition product in very good yield (Scheme 41). Enynes [110][111][112][113][114][115][116], diynes [117][118][119][120], allenynes [121][122][123][124][125][126][127][128], and dienes [129][130][131] are common substrates for intramolecular cycloaddition reactions. Porcel et al. found that

• the [4 + 3] and [4 + 2] cycloadducts (225 and 226) [101]. The selectivity was improved to 96:4 in favor of the [4 + 3] cycloadduct when di-tert-butylbiphenylphosphinegold(I) was employed as the catalyst. On the other hand, the use of arylphosphitegold(I) complexes exclusively produced the formal [4

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• transfer of 2-alkynyl-1,5-diketones. The discovery of a [4 + 2] cycloaddition of a furanium intermediate to a carbonyl group was further verified by quantum chemical calculations. The competing [2 + 2] and [4 + 2] reaction coordinates were computed for the simplified substrate 11a, shown in Scheme 10. In

Synthesis of cross-conjugated trienes by rhodium-catalyzed dimerization of monosubstituted allenes

• Tomoya Miura,
• Tsuneaki Biyajima,
• Takeharu Toyoshima and
• Masahiro Murakami

Beilstein J. Org. Chem. 2011, 7, 578–581, doi:10.3762/bjoc.7.67

• used for consecutive double [4 + 2] cycloaddition reactions [2][3][4] to provide a rapid access to polycyclic carbon frameworks. Thus, a number of methods for the preparation of the parent 3-methylenepenta-1,4-diene [5] and its substituted derivatives [6][7][8][9][10][11][12][13][14][15][16][17] has

• dimerization reaction, in contrast to the nickel-catalyzed reaction [18][19]. Next, we examined the consecutive double [4 + 2] cycloaddition reaction of the cross-conjugated trienes obtained in the present study. Triene 3a was treated with 4-phenyl-1,2,4-triazoline-3,5-dione (4, PTAD), a highly reactive

• tetracyanoethylene (6, TCNE), which was a less reactive dienophile than 4, was used, [4 + 2] cycloaddition also occurred preferentially at site β, but only once on heating at 60 °C for 24 h. Conclusion In summary, we have developed a new dimerization reaction of monosubstituted allenes catalyzed by a rhodium(I)/dppe

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• + 2] cycloaddition (Diels–Alder reaction) is only very rarely observed photochemically (vide infra). Photocycloadditions are not limited to simple alkenes, and even the thermally very stable benzene core has been shown to become quite reactive upon excitation with photons. It can be converted into

• known representatives are undoubtedly the [2 + 2] photocycloaddition, forming either cyclobutanes or four-membered heterocycles (as in the Paternò–Büchi reaction), whilst excited-state [4 + 4] cycloadditions can also occur to afford cyclooctadiene compounds. On the other hand, the well-known thermal [4

End game strategies towards the total synthesis of vibsanin E, 3-hydroxyvibsanin E, furanovibsanin A, and 3-O-methylfuranovibsanin A

• Brett D. Schwartz,
• Craig M. Williams and
• Paul V. Bernhardt

Beilstein J. Org. Chem. 2008, 4, No. 34, doi:10.3762/bjoc.4.34

• -hydroxyvibsanin E (13), furanovibsanin A (14), and 3-O-methylfuranovibsanin A (15) (Figure 2) building on core structures 10–12 (Figure 2). Results and Discussion As shown in the first generation retrosynthesis (Scheme 1) a [4+2] cycloaddition to install the required functionality was envisaged. All attempts

• , however, to procure this transformation (i.e. 16), that is reaction of isoprene and oxygenated derivatives, with enone 12 completely failed. Davies [16][17], however, demonstrated that a photochemical assisted thermal [4+2] cycloaddition does proceed but with incorrect relative stereochemistry and limited

Sordarin, an antifungal agent with a unique mode of action

• Huan Liang

Beilstein J. Org. Chem. 2008, 4, No. 31, doi:10.3762/bjoc.4.31

• overall yield of 2%. Mander’s synthesis of sordaricin As early as 1991, Mander reported model studies [24][25] for sordaricin synthesis using intramolecular [4+2] cycloaddition, and this work culminated in a total synthesis of Sordaricin in 2003 [14][15]. Scheme 4 depicts Mander’s retrosynthetic analysis

High stereoselectivity on low temperature Diels- Alder reactions

• Luiz Carlos da Silva Filho,
• Valdemar Lacerda Júnior,
• Mauricio Gomes Constantino,
• Gil Valdo José da Silva and
• Paulo Roberto Invernize

Beilstein J. Org. Chem. 2005, 1, No. 14, doi:10.1186/1860-5397-1-14

• unsubstituted and α- or β-methyl substituted 2-cycloenones was also observed. Introduction For more than 70 years, the Diels-Alder reaction, or [4+2] cycloaddition reaction, has remained as one of the best powerful organic transformations in chemical synthesis, particularly in obtaining polycyclic rings. Many