Regioselective S_N2' Mitsunobu reaction of Morita–Baylis–Hillman alcohols: A facile and stereoselective synthesis of α-alkylidene-β-hydrazino acid derivatives

• Silong Xu,
• Jian Shang,
• Junjie Zhang and
• Yuhai Tang

Beilstein J. Org. Chem. 2014, 10, 990–995, doi:10.3762/bjoc.10.98

• , delivering the hydrazines 3e–i in high yields (79–91%) and excellent E/Z selectivity, with an exception of the nitro-substituted 1g giving a moderate E/Z ratio (Table 2, entries 4–8). An ortho substituent on the benzene ring of the MBH alcohol was also well tolerated (Table 2, entry 5 vs 6). Notably, in

• , producing the corresponding α-alkylidene-β-hydrazino esters 3 in high yields (80–90%) and good E/Z selectivity (Table 2, entries 9–18). An exception was observed for the reaction of MBH alcohol 1j with tert-butyl azodicarboxylate (2c), which gave 55% yield and a modest E/Z ratio (5:1) (Table 2, entry 14

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• olefinating reagents) and 2) E/Z-selectivity of the reaction. Moriwake et al. noticed in their synthesis of vinylglycinol 64 that the reaction of methyltriphenylphosphonium bromide with KH as the base provided 62 in fairly good yield, but with complete racemization of the product (Scheme 25) [101]. This

• results, McKillop [27] noticed that with KHMDS as the base, there was no epimerization at all! To prepare “salt-free” ylides, it is necessary to remove lithium halide from the reaction solution. On the other hand KHMDS is a convenient base for the preparation of “salt-free” ylides. High Z-selectivity is a

• typical outcome with unstabilized ylides. Kim has investigated means of reversing the E/Z-selectivity to favour the E-isomer [104]. They noticed that olefination under the usual Wittig conditions provided high Z-selectivity (1:15 E/Z). When the reaction was quenched with MeOH at −78 °C, the E/Z-ratio was

Recent advances in transition metal-catalyzed Csp²-monofluoro-, difluoro-, perfluoromethylation and trifluoromethylthiolation

• Grégory Landelle,
• Armen Panossian,
• Sergiy Pazenok,
• Jean-Pierre Vors and
• Frédéric R. Leroux

Beilstein J. Org. Chem. 2013, 9, 2476–2536, doi:10.3762/bjoc.9.287

• decarboxylative fluoroalkylation (Table 1) [61]. A wide range of α,β-unsaturated carboxylic acids afforded the corresponding difluoromethylated alkenes in high yields and with excellent E/Z selectivity. The putative mechanism for this copper-catalyzed decarboxylative fluoro-alkylation involves the iodine–oxygen

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• selectivity, in 10 steps and 35% overall yield. It was found that the use of freshly distilled THF in the Takai olefination and careful temperature control in the subsequent cross coupling were critical to the preservation of high E/Z selectivity over the course of these transformations. Once isolated

• Takai olefination [36] was used to generate the E-vinyl iodide. The vinyl iodide was sufficiently stable for purification by silica gel chromatography but, following purification, was immediately carried forward to a Sonogashira reaction with propyne [37]. The enyne could be obtained in 15:1 E/Z

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

• effectively formed, and the background reaction giving the racemic product proceeded. Additionally, the high Z-selectivity of product 9Ba indicates that the stereoselective iodine-atom transfer from isopropyl iodide to an intermediate radical proceeded effectively under these catalytic reaction conditions

• solvent MeOH gave the nearly racemic product, although the high Z-selectivity was maintained (Table 1, entry 10). These results suggest that the rigid chelation of the chiral Lewis acid to the hydroxamate ester functionality occured in CH2Cl2. In the presence of chiral Lewis acid, hydroxamate ester 6C had

• conditions, an outstanding level of enantioselectivity was observed on employing the bulky tert-butyl iodide as a radical precursor (Table 1, entry 14). A good yield of the product 9Bd was obtained with 92% ee and high Z-selectivity. The absolute configuration at the newly generated stereocenters of 9Aa–Bd

Alternaric acid: formal synthesis and related studies

• Michael C. Slade and
• Jeffrey S. Johnson

Beilstein J. Org. Chem. 2013, 9, 166–172, doi:10.3762/bjoc.9.19

• more step-efficient endgame, test substrates were prepared for exploration of a modified Julia olefination [32]. As shown in Scheme 4, the phenyltetrazole heteroaromatic core in sulfones 9a and 9b provided excellent E-/Z- selectivity for formation of the C8–C9 olefin under typical modified Julia

Highly selective synthesis of (E)-alkenyl-(pentafluorosulfanyl)benzenes through Horner–Wadsworth–Emmons reaction

• George Iakobson and
• Petr Beier

Beilstein J. Org. Chem. 2012, 8, 1185–1190, doi:10.3762/bjoc.8.131

• E/Z selectivity, but called for rather long reaction time. By changing the solvent from DMF to THF, we observed a less efficient first step (the VNS reaction) with many unidentified side products being formed (Table 1, entry 2). Therefore, all other experiments were carried out starting from

• increased the reaction rate, presumably by better solubilization of KOH and the formed potassium diethylphosphate, and gave the required product 5a in 84% isolated yield and high E/Z selectivity (Table 1, entry 13). Using optimized reaction conditions (Table 1, entry 13), the scope of the HWE reaction of

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

• activity of Gagosz’s complex [(Ph3P)AuNTf2] in terms of yield and selectivity. Starting from arylcyclopropenylmethyl acetates 39a–39e substituted by a phenyl group or an electron-deficient aromatic ring, a low temperature (CH2Cl2, −50 °C) was essential to obtain the 2-acetoxydienes 40a–40e with high Z

• -selectivity (Z/E = 10:1–41:1). Cyclopropenylmethyl acetate 39f substituted by the electron-rich p-tolyl group effectively underwent rearrangement, but the corresponding diene 40f decomposed rapidly. A low selectivity (Z:E = 1.8:1) was observed for the 2-acetoxydiene 40g resulting from the rearrangement of

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

• the thermal and acidic conditions were investigated as shown in Table 1. Allenamide 1 smoothly underwent isomerization via a 1,3-hydrogen shift when heated at 115 °C in CH3CN (sealed tube) to give the desired 2-amido-diene product 2 in 78% isolated yield with a 16:1 E/Z selectivity (Table 1, entry 1

• ). There appears to be some solvent effect on the E/Z selectivity with more polar solvents providing the best ratio (Table 1, entries 2–4). In addition to thermal conditions, we screened several Brønsted acids at room temperature in order to investigate a milder condition. While PTSA resulted in poor E/Z

• ratio (Table 1, entry 5), a range of Brønsted acids were quite effective in affording the desired 2-amido-diene 2 (Supporting Information File 1 and Supporting Information File 2) with excellent E/Z selectivity [Table 1, entries 6–9]. After having established the 1,3-hydrogen shift under thermal and

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites

• Christophe Copéret

Beilstein J. Org. Chem. 2011, 7, 13–21, doi:10.3762/bjoc.7.3

• ][17][18]; one of the most important and difficult targets is the control of the configuration of the double bond, the E- and Z-selectivity. Most often, high selectivity is only obtained for specific substrates, where thermodynamics favour one isomer, often that with an E-configured double bond

• particular, with the bulky X = NPh2 and small imido ligands (N-adamantyl), Z-selectivity is achieved, albeit never exceeding 67% [(E/Z) = 0.5]. While low, it shows that it should be possible to control the stereoselectivity by using the right combination of ligands. Note also that these low selectivities are

• ) ranging between 0.05 (> 95%, diastereoselectivity excess (de) > 90%) and 0.8 (55%, de = 10%), depending on the solvent (THF > toluene > heptane, Table 2); the best compromise between activity and selectivity being achieved in toluene. This Z-selectivity can be interpreted as a way to minimize interactions

Single and double stereoselective fluorination of (E)-allylsilanes

• Marcin Sawicki,
• Angela Kwok,
• Matthew Tredwell and
• Véronique Gouverneur

Beilstein J. Org. Chem. 2007, 3, No. 34, doi:10.1186/1860-5397-3-34

• on these substrates influence the E/Z selectivity of the resulting allylic fluorides (Table 1). For the (E)-allylsilane 1a, the allylic fluoride 2a was obtained in 81% yield as a roughly 1/1 mixture of E/Z geometrical isomers (entry 1). The structurally related (E)-allylsilane 1b possessing the