Radical carbonylations using a continuous microflow system

• Takahide Fukuyama,
• Md. Taifur Rahman,
• Naoya Kamata and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2009, 5, No. 34, doi:10.3762/bjoc.5.34

• demonstrated by our group [4][5][6] as well as others [7][8][9][10][11]. In our recent report, we demonstrated that excellent thermal efficiency of the microflow system would lead to effective execution of tin hydride and TTMSS (tris(trimethylsilyl)silane)-mediated radical reduction and cyclization reactions

• yields of the desired products. Carbon monoxide is an important feedstock and our group has actively pursued carbonylation reactions [14][15][16][17]. Thermally induced radical carbonylations using tin hydride usually require pressurized CO conditions to ensure that the concentration of CO around the

• radical centers is high enough to compete with the premature quenching by tin hydride (Scheme 1). Encouraged by our previous successes with both radical reactions [12] and metal-catalyzed carbonylation reactions using microflow devices [18][19][20], we decided to examine a continuous microreaction system

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions

• Rajeev K. Shrivastava,
• Elise Maudru,
• Gurdial Singh,
• Richard H. Wightman and
• Keith M. Morgan

Beilstein J. Org. Chem. 2008, 4, No. 43, doi:10.3762/bjoc.4.43

• is some 40 times slower than the counterpart 5-hexenyl cyclisation [15][16][17][18][19]. In the case of the 6-hexenyl radical this results in the attack of the acyclic radical on the tin reagent becoming a more effective process compared to the 5-hexenyl case. An additional problem is that a 1,5

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

• and its efficiency. However, this procedure suffers from crippling drawbacks in terms of toxicity, cost, disposal, and tedious purification to remove tin residues. [6][7][8][9][10] However, we recently faced limits to the use of some of these methods for reductive removal of S-alkyl O-ethyl

Solvent- controlled regioselective protection of allyl- 4,6-benzylidene glucopyranosides

• Kerry Ann Ness and
• Marie E. Migaud

Beilstein J. Org. Chem. 2007, 3, No. 26, doi:10.1186/1860-5397-3-26

• functional group manipulations required to access suitable synthetic precursors. For hexopyranoses, acylation of cis-diols can be achieved with high regioselectivity either by means of metal activators such as tin [1][2][3], silver [4], boron [5] or copper [6] or by exploiting the relative reactivity of

• hydroxyl groups [7][8]. However, metal-promoted alkylation and base-catalysed acylation of diols have proven to be highly undependable in the case of glucose and other cyclic trans-diols, where both hydroxyl groups are equatorial. For instance, reports of identical procedures describing the tin-catalysed

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• and Hunig's base; tin (IV) chloride[27] and N-bromosuccimide[28] were all tested but none were successful as either no reaction occurred or the alkene was halogenated as well as the conversion of the silane to the silyl chloride. Further, given that the major product from many of the methods attempted

Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• key step is the syn addition of the tin cuprate to the acetylene, which controls the cis stereochemistry required for cyclization. [23] Seven Membered Carbocycles The use of nitriles and imines as electrophiles in the silylcupration of allene provides new alternatives for carbocyclization. Recently

Generation of pyridyl coordinated organosilicon cation pool by oxidative Si-Si bond dissociation

• Toshiki Nokami,
• Ryoji Soma,
• Yoshimasa Yamamoto,
• Toshiyuki Kamei,
• Kenichiro Itami and
• Jun-ichi Yoshida

Beilstein J. Org. Chem. 2007, 3, No. 7, doi:10.1186/1860-5397-3-7

• was found that the introduction of a coordinating group such as a pyridyl group decreased the oxidation potential of tetraalkylstannanes, although there is no indication of the coordination in the neutral molecule. Dynamic intramolecular coordination to tin seems to facilitate electron transfer [22

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• provide unequivocal evidence for the fragmentation of such radicals to give ketones and acyl or alkoxycarbonyl radicals. Instead, standard reduction predominates, even at low tin hydride concentrations. Some ketone product is formed in the α-acyloxy substrate at low concentrations, but it is unclear

• give 15 and 16a,b is the competition step, and a standard plot of the ratio of products as a function of tin hydride concentration should provide a straight line passing through the origin if radical fragmentation competes with reduction. Alternatively, oxidation of 13a,b to cation 17a,b will

• conditions, as detailed in the Supporting Information. Briefly, stock solutions of the iodide 11a,b (1 equiv) and Bu3SnH (1.1 equiv) in C6H6 or C6D6 were diluted to the required concentration of tin hydride, then AIBN (0.2 equiv) and p-dimethoxybenzene (0.1–0.2 equiv, internal standard) were added. The