Gold(I)-catalyzed synthesis of γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols

• Michel Chiarucci,
• Mirko Locritani,
• Gianpiero Cera and
• Marco Bandini

Beilstein J. Org. Chem. 2011, 7, 1198–1204, doi:10.3762/bjoc.7.139

• alkylation procedure to obtain valuable precursors (i.e., lactams and lactones) of podophyllotoxin analogs [39][40]. However, to the best of our knowledge, no examples of metal-catalyzed lactonization through direct activation of allylic alcohols have been described so far. Results and Discussion At the

• conditions (Table 1). Initial attempts to perform the lactonization reaction of 1a were carried out by means of a silver-free cationic complex [P(t-Bu)2o-biphenyl](AuCH3CN)SbF6 (5 mol %). The desired butyrolactone 2a was obtained selectively under reflux in DCE for 16 h (entry 1), although only in low yield

• lactonization (Table 2). The impact of the carbon–carbon double bond configuration on both chemical and stereochemical outputs of the process was initially investigated. Here, by subjecting (E)-1a to the reaction conditions A (i.e., IMesAuCl/AgOTf, DCE, 80 °C) the corresponding lactone 2a was isolated in

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• complex [RuCl2(=CHPh)(SIMes)(PCy3)], CuCl, and dHbipy (SIMes is 1,3-dimesitylimidazolin-2-ylidene, dHbipy is 4,4'-di-n-heptyl-2,2'-bipyridine) was able to promote the ATRA of trichloroacetic acid onto cyclopentadiene followed by a lactonization into 3,3-dichloro-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan

• -2-one (18). These results prompted us to examine the cascade RCM/decomposition/ATRA/lactonization of substrate 16 into dichloro compound 18 with homobimetallic complex 1 under mild thermolysis conditions. Thus, the substrate and the catalyst precursor (5 mol %) were dissolved in toluene and heated

Systematic investigations on the reduction of 4-aryl-4-oxoesters to 1-aryl-1,4-butanediols with methanolic sodium borohydride

• Subrata Kumar Chaudhuri,
• Manabendra Saha,
• Amit Saha and
• Sanjay Bhar

Beilstein J. Org. Chem. 2010, 6, 748–755, doi:10.3762/bjoc.6.94

• keto and ester moieties kept far apart for lactonization due to trans-geometry of the olefinic linkage) was treated with NaBH4 (4 equiv) in methanol. However, this reaction unexpectedly led to the exclusive formation of 2a. With a smaller amount (2 equiv) of NaBH4 in methanol, compound 1g gave 9 and 2a

• nucleophilic attack of the hydride is therefore not feasible. As a consequence, the –OH and –COO− are too far apart to interact with each other. Therefore a single bond between the carbinol carbon and carboxylic acid moiety is impossible and hence no possibility of rotation, lactonization and subsequent

• -oxoester to 1,4-diols was finally established (Scheme 11) when substrate 14 [40] (incapable of lactonization due to distal spatial disposition of the oxo- and methoxycarbonyl moieties imposed by the rigidity of the cyclopropane ring system) underwent selective reduction of the oxo-functionality only under

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

• resulting aldol product was desilylated and in situ lactonization gave 110. Removal of the MOM groups afforded longicin (101), which was identical to the natural product on the basis of the reported physical constants [49]. Total synthesis of murisolin Murisolin (111) is a mono-THF acetogenin, isolated from