Heteroorganic betaines. 6. Structure and reactivity of silicon-containing organophosphorus betaines with the –S—Si—C—P+ fragment: a DFT study

The structures of silicon-containing organophosphorus betaines ^–S—SiR¹ ₂—CR² ₂—P⁺R³ ₃ and their ylide isomers were calculated using the density functional approach with the gradient-corrected PBE functional and extended TZ2P basis set. Three possible pathways of thermal decomposition of these betaines were analyzed. These are (i) cleavage of the central C—Si bond with the formation of a Wittig ylide and silanethione, (ii) intramolecular nucleophilic S _N-substitution with elimination of phosphine PR³ ₃ and the formation of silathiirane (the Corey—Chaikovscky transformation), and (iii) a Wittig-type decomposition followed by the formation of substituted silaethylene.The structures of products and transition states of these reactions were calculated. The cis-gauche conformation of the ^–S—Si—C—P⁺ fragment of betaines was found to be the most stable. This is in agreement with the results of X-ray diffraction study and can be rationalized by strong Coulomb attraction between the cationic and anionic centers. The betaines are stable toward retro-Wittig thermal decomposition. The Corey—Chaikovscky formation of thiirane is preferable under conditions of thermal decomposition. Retro-Wittig-type decomposition of betaines followed by the formation of silanethione is favored by intra- and intermolecular coordination of donor ligands.     

Heteroorganic betaines. 7. Synthesis and structure of a germanium-containing organophosphorus betaine Et3P+—CHMe—GeMe2—S–

Germanium-containing organophosphorus betaine Et₃P⁺—CHMe—GeMe₂—S^– was synthesized by the reaction of hexamethylcyclotrigermatrithiane with Et₃P=CHMe. The structure of the betaine was established by X-ray diffraction analysis and multinuclear NMR spectroscopy. In the crystal, the P⁺—C—Ge—S^– main chain of the molecule adopts a folded cis-gauche conformation due to strong Coulomb interactions between the anionic and cationic centers. The equilibrium geometry of the isolated molecule was calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set). The calculated geometric characteristics are in qualitative agreement with the X-ray data. The structure of the betaine is compared with the structure of its silicon-containing analog studied previously.     

Synthesis of arsonium salts and betaines based on triphenylarsine and ω-bromoalkanoic acids

The reactions between Ph₃As and ω-bromoalkanoic acids with the length of polymethylene fragment n = 5, 7, 9 afford quaternary arsonium salts. Their treatment with alkali gives biologically active arsenobetaines. Solvent-free reactions of Ph₃P or Ph₃As with 2,3-dibromopropionic acid lead to the corresponding arsonium and phosphonium salts bearing (CH₂)₂COOH substituent.     

R—四氢噻唑—2—硫酮—4—羧酸同R.S—氨基醇的手性识别反应

Ｒ－四氢噻唑－２－硫酮－４－羧酸同Ｒ．Ｓ－亮氨醇、Ｒ．Ｓ－蛋氨醇、Ｒ．Ｓ－苯丙氨醇和Ｒ．Ｓ－色氨醇反应分别得到光学活性非对映体过剩的铵盐；Ｒ－四氢噻唑－２－硫酮－４－羧酸．Ｓ－色氨醇，同时分离出光学活性对映体过剩的Ｒ－亮氨醇，Ｓ－氨蛋醇，Ｓ－苯丙氨醇及Ｒ－色氨醇，用半经验的量子化学ＰＭ３方法研究了氨基醇的最优构型和电子结构，得到了铵盐的最优几何构型。     

Spirocyclic betaines or 2-amino-Δ2-1,3,4-thiadiazoline-5-acetic acid and their rearrangement in acetic anhydride

Reaction of N-(1-pyrrolidinyl)-, N-(1-piperidinyl)-, N-(4-morpholinyl)-, and N-(1-hexahydroazepinyl)-thioureas with propiolic acid gives hetero-N-spiro-4-(2-amino-²-1,3,4-thiadizolin-4-io-5-acetates), which rearrange in acetic anhydride to 2-(N-heteryl)imino-2,3-dihydro-4H-1,3-thiazin-4-ones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 263–265, February, 1993.     

Synthesis of （2R,4R）—2—N—tert—Butyloxycarbonyl Amino—4,5—epoxido—valeric Acid Methyl Ester

The stereoselective synthesis of (2R,4R)-2-N-tert-butyloxycarbonyl amino-4,5-epoxido-valeric acid methyl ester 8,which is the key intermediate for the synthesis of (2′S,2R)-3-trans-nitrocyclopropyl-alanine,was first accomplished.     

著名有机化学家R.B.伍德沃德

著名的美国有机化学家,哈佛大学的R.B.伍德沃德教授于1979年7月8日因患心脏病突然逝世了。他是当代有机化学的大师之一,由于对有机合成的重大贡献,曾荣获1965年度诺贝尔化学奖。他的不幸逝世使世界化学界感到极其惋惜,因为他正当盛年,近年来不断有重