Conversion of Stilbene to trisubstituted Olefins

Determination of the stereochemistry of bromination-dehydrobromination of both cis and trans-stilbene has been achived. Coupling of the resulting vinyl bromides with alkyl or aryl groups have been done. The coupling products could serve as intermediates for the synthesis of biologically active tetrasubstituted olefins.     

Reaction of di- and trisubstituted ethynylsilanemagnesium halides with dimethylethynylfluorosilane

Conclusions The reaction of magnesium bromide derivatives of di- and triethynylsilanes with dimethylethynylfluorosilane gave 1,2-disubstituted silylacetylenes containing ethynyl and vinyl groups at the silicon atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2614–2616, November, 1984.     

Intermolecular C-H functionalization versus cyclopropanation of electron rich 1,1-disubstituted and trisubstituted alkenes

Rhodium(II)-catalyzed reactions of aryldiazoacetates with electron rich 1,1-disubstituted and trisubstituted alkenes were systematically studied. The regio-, diastereo- and enantioselectivity of the chemistry was profoundly influenced by the nature of the substrates and the catalyst. Conditions were developed for either selective cyclopropanation or C-H insertion. Both reactions can be achieved with high diastereo- and enantioselectivity (for C-H insertion: >90% de, up to 96% ee, for cyclopropanation: >94% de, up to 95% ee). For the 1,1-disubstituted vinyl ethers, cyclopropanation occurs with variable diastereoselectivity but in optimized systems the cyclopropane is formed in >94% de and up to 98% ee.     

Synthesis of trisubstituted furans from epoxypropargyl esters by sequential SmI2-promoted reduction-elimination and Pd(II)-catalyzed cycloisomerization.

A two-step one-pot synthesis of 2,3,5-trisubstituted furans 8 from 4,5-epoxyalk-2-ynyl esters 6 is described. The sequence is initiated by a SmI2-promoted reduction that takes advantage of the ability of the alkynyloxirane moiety present in 6 to accept electrons from SmI2. The resulting organosamarium species then eliminates an adjacent acetate or benzoate leaving group, leading to the formation of unstable 2,3,4-trien-1-ols 7. Without isolation, these are cycloisomerized to furans 8 by treatment with a catalytic amount of a Pd(II) complex and a proton source. The whole sequence takes place under mild reaction conditions. Some useful functional groups such as cyano and alpha,beta-unsaturated esters are tolerated, but benzyl- and silyl-protected hydroxyl groups are deprotected to some extent. Starting materials can be easily assembled using reliable reactions from acetylene, an aldehyde or ketone, and a vinyl halide fragment. This offers the possibility of introducing branched substituents at C-5 of the furan ring.     

Catalytic asymmetric synthesis of trisubstituted aziridines

A method is described which provides for the direct asymmetric catalytic synthesis of trisubstituted aziridines from imines and diazo compounds. While unactivated imines were not reactive to α-diazo carbonyl compounds in which the diazo carbon was disubstituted, N-Boc imines react with both α-diazo esters and α-diazo-N-acyloxazolidinones to give trisubstituted aziridines with excellent diastereo- and enantioselectivities.     

Highly enantioselective cyclopropanation of trisubstituted olefins

A highly efficient asymmetric cyclopropanation of trisubstituted olefins with methyl diazoacetate has been developed in terms of an elaborate modified chiral bisoxazoline/copper complex as a catalyst. A broad scope of substrates is compatible with this catalyst system, including various trisubstituted olefins bearing different aryl-, fused aryl- and alkyl-substituents, providing an easy access to optically active 1,1-dimethyl cyclopropanes in good yields with excellent diastereo- and enantio-selectivity.     

Parallel solid-phase synthesis of trisubstituted triazinobenzimidazolediones

An efficient method for the solid-phase synthesis of trisubstituted [1,3,5]triazino[1,2-a]benzimidazole-2,4(3H,10H)-diones from resin-bound amino acids is described. N-acylation of the primary amine of a resin-bound amino acid with 4-fluoro-3-nitrobenzoic acid, followed by displacement of the fluoro group and reduction of the nitro group, generated a resin-bound o-dianilino derivative. The dianilino compound was treated with cyanogen bromide to generate the corresponding iminobenzimidazole, which, following treatment with N-(chlorocarbonyl)isocyanate, afforded the resin-bound triazinodione derivative. Alkylation of the triazinodione compound with an alkyl halide yielded, following cleavage of the solid-support, the trisubstituted [1,3,5]triazino[1,2-a]benzimidazole-2,4(3H,10H)-dione.     

Organocatalytic stereoselective epoxidation of trisubstituted acrylonitriles

The first diastereospecific and enantioselective epoxidation of trans-2-aroyl-3-arylacrylonitriles by means of the commercially available diaryl L-prolinol/tert-butyl hydroperoxide system has been developed. These diversely functionalized epoxides were obtained in excellent yield (up to 99%), complete diastereoselectivity for the trans-isomer, and good enantioselectivity (up to 84% ee). Highly enantioenriched epoxides can be easily obtained after a single crystallization (ee > 90%).     

The markovnikoff hydroboration of a trisubstituted olefin

Hydroboration-oxidation of akuammicine $\text{1}$ mainly gave the tertiary alcohol $\text{2}$ Hydroboration-oxidation of double bonds is a well known anti-Markovnikoff process^1,2. In the course of applications of this method to the indole alkaloid field, the following Markovnikoff hydration of a trisubstituted olefin was surprisingly observed :

     

Synthesis of trisubstituted alkenes via olefin cross-metathesis

[formula: see text] Trisubstituted alkenes have been prepared for the first time via intermolecular olefin cross-metathesis, using 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ruthenium alkylidene complexes 3a,b in good yields with moderate E selectivity. In addition, protected alcohols near the geminal disubstituted olefin improve reactivity for cross-metathesis.     

Theoretical investigation of the symmetric trisubstituted borazines

The bonding in borazine and four symmetric tri-substituted derivatives, B-trifluoroborazine, N-trifluoroborazine, B-trimethylborazine and N-trimethylborazine, is discussed by means of all electron ab initio SCFMO calculations. B-trifluoroborazine is predicted to be 12·9 eV more stable than the N-trifluoro derivative and B-trimethylborazine 2·8 eV more stable than the N-trimethyl derivative. The calculated wavefunctions are used to interpret the low energy photoelectron spectra of these molecules. The calculated sequence for the three highest filled orbitals is πσπ in all derivatives except B-trifluoroborazine, where the sequence ππσ is realised.     

三取代环丙烷的^1^3C核磁共振谱研究

前文曾报道三取代环丙烷的质子核磁共振谱及其解析结果,讨论了取代基对化学位移和偶合常数的影响.环丙烷的~(13)C核磁共振谱研究报道极少。Monti等人研究了甲基、溴代和乙炔基环丙烷的~(13)C核磁共振谱,发现在多取代的环丙烷中,取代基相互之间的影响是很显著的.Clague等人亦报道了一系列环丙烷的~(13)C核磁共振谱,但未有详细的分析.本文报道10种尚未见载于文献的三取代环丙烷的~(13)C核磁共振谱,数据见表1. 在1,2,3-三取代环丙烷中,由于取代基的相互作用,影响环上碳的化学位移的因素是比较复杂的.从我们测定化合物的数据来看,取代基为CH_3的环上碳的平均化学位移为29.24     

Single isomer trisubstituted olefins bearing alkyl groups

E-β-Chloro-α-iodo-α,β-unsaturated esters were converted to single isomer trisubstituted olefins bearing alkyl substituents by using and alkyl-Suzuki cross coupling. The process was highly selective, and the products in all cases were isolated as single isomers. Mechanistic investigations indicated that this process transfers a hydrogen from water to the α-position of the substrate, and then an alkyl group is introduced to the β-position of the intermediate template while replacing a chloride.     

A short approach to trisubstituted γ-butyrolactones

The dihydroxylation of unsaturated aldol adducts with catalytic OsO₄ and NMO occurs under very mild conditions and with moderate to excellent levels of diastereoselectivity to give trisubstituted γ-butyrolactone derivatives.