Die heterolytische Fragmentierung als Reaktionstypus in der organischen Chemie

9-Membered Carbocycles: Strategies and Tactics for their Synthesis

Many natural products comprising a nine-membered carbocyclic core structure exhibit interesting biological effects. However, only a minority have succumbed to their synthesis in the past. The synthesis of functionalized nine-membered carbocycles still remains a challenging goal for synthetic chemists, mainly due to their high ring strain. Different strategies to overcome the unfavorable enthalpic and entropic factors associated with their formation are highlighted in this Concept article. The presented methods are classified into two different categories: (1) the ring-expansion of smaller rings or the ring-contraction of larger rings and (2) the direct cyclization of acyclic precursors.

Novel diaminopropyl substituted organotin compounds

A novel synthetic pathway involving the desilylation of a tin trimethylsilyl species (Ph2Sn(SiMe3)2) towards nonprotected di(3-aminopropyl)tin dichloride ((H2N(CH2)3)2SnCl2) is described. Di(3-aminopropyl)tin dichloride is then converted to the respective dicarboxylates species (H2N(CH2)3)2Sn(OCOR)2 containing carboxylic acids of different lengths (R = –CH3, –(CH2)10CH3). Depending on the nature of R, discrete packing effects are observed in the solid state of di(3-aminopropyl)tin dicarboxylate derivatives. All the synthesized substances were characterized by 1H, 13C, and 119Sn nuclear magnetic resonance data and also single crystal X-ray analysis. These compounds are a promising class of substances for biological, pharmaceutical, and technical applications.

Novel amino propyl substituted organo tin compounds

In this work, a new synthetic pathway yielding unprotected amino propyl tin compounds is described. For this purpose, mono stannanes with different substitution patterns are used. In a first step, tin hydrides are deprotonated using lithium diisopropyl amide and mixed with an electrophile containing a protected amine in the ω-position. After deprotection via acidic hydrolysis, the desired amino propyl tin compounds are obtained in high yield and purity. The thermal reaction behavior of the amino propyl tin hydrohalide intermediates containing one aromatic residue at the central tin atom is also investigated. For this purpose, amino propyl tin hydrohalides are heated under vacuum until the aromatic hydrocarbon is liberated. This thermal treatment leads to so far unknown tin halides containing an amino propyl side chain. For all of these substances detailed liquid 1H, 13C, and 119Sn-nuclear magnetic resonance (NMR) data were obtained, and in one case solid state NMR is also conducted. Regarding solids, single crystal X-ray analysis is performed. Some derivatization reactions with these new substances are demonstrated, especially the synthesis of an amino propyl tin carboxylate, which might be very interesting for biological, pharmaceutical, or technical processes.

C-C fragmentation: origins and recent applications

It has been 60 years since Eschenmoser and Frey disclosed the archetypal CC fragmentation reaction. New fragmentations and several variants of the original quickly followed. Many of these variations, which include the Beckmann, Grob, Wharton, Marshall, and Eschenmoser-Tanabe fragmentations, have been reviewed over the intervening years. A close examination of the origins of fragmentation has not been described. Recently, useful new methods have flourished, particularly fragmentations that give alkynes and allenes, and such reactions have been applied to a range of complex motifs and natural products. This Review traces the origins of fragmentation reactions and provides a summary of the methods, applications, and new insights of heterolytic CC fragmentation reactions advanced over the last 20 years.

Total Synthesis of (±)-Pallavicinin and (±)-Neopallavicinin

Through a biomimetic pathway, (+/-)-pallavicinin and (+/-)-neopallavicinin were synthesized from (+/-)-Wieland-Miescher ketone via Grob fragmentation, intramolecular aldol cyclization, and intramolecular Michael reaction. The synthesis was stereocontrolled efficiently and followed the stereochemistry of the Wieland-Miescher ketone, and could provide opportunities for access to analogues of pallavicinin, neopallavicinin, and other related bioactive diterpenoids.

Stereoselective halogenation of the 16-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17-ols and their solvolytic investigation

The primary hydroxy functions of 16alpha-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17beta-ol (3a) and 16beta-hydroxymethyl-3-methoxy-13alpha-estra-1,3,5(10)-trien-17alpha-ol (4a) were stereoselectively transformed into good leaving groups. On alkaline methanolysis of the 16-halomethyl or 16-tolylsulfonyloxymethyl derivatives, a new D-seco-13alpha-estrone derivative was obtained in high yield.

Synthesis and receptor-binding examinations of the normal and 13-epi-D-homoestrones and their 3-methyl ethers

An effective epimerization of the normal estrone 3-methyl and 3-benzyl ethers by using o-phenylenediamine and AcOH made the possibility for facile entry into the 13alpha-estrone series. Combination of this synthetic methodology with an isolation step carried out by means of the Girard-P reagent, the corresponding ethers of 13-epi-estrone were obtained in excellent yields. The 3-hydroxy and 3-methoxy D-homoestrone derivatives in both the normal and the 13alpha-estrone series were then synthesized and tested in vitro in a radioligand-binding assay. The estrogen receptor recognizes these compounds, but their relative binding affinities (RBAs) are lower than that of the reference compound 3,17beta-estradiol. The progesterone receptor-binding affinities of the four D-homo derivatives were also tested showing low values for 13alpha-D-homoestrone and its 3-methyl ether. Pharmacologically, these 13alpha-D-homoestrone derivatives are estrogen receptor-selective molecules.