Synthesis unsymmetrical analogs

A similar strategy was used for the synthesis of unsymmetrical analogs of BEDO-TTF 690 <1996S26>. 

Several approaches to enantioselective synthesis have been taken, but the most efficient are those that use chiral catalysts to temporarily hold a substrate molecule in an unsymmetrical environment—exactly the same strategy that nature uses when catalyzing reactions with chiral enzymes. While in that unsymmetrical environment, the substrate may be more open to reaction on one side than on another, leading to an excess of one enantiomeric product over another. As an analog)7, think about picking up a coffee mug in your... 

Preparative routes to 5/7-dibenz[6,e]azepine-6,11 -diones (morphanthridinediones) are based mainly on the cyclization of 2-aminobenzophenone-2 -carboxylic acids and their derivatives (55LA(594)89). Studies on a-aminodiphenyImethane-2 -carboxylic acid reveal that cyclization to 5,11 -dibenz[6,e ]azepinone (188) is much slower at room temperature than the cyclizations of the analogous 2-aminobiphenyl-2 -carboxylic acid and the 2 -aminobiphenylacetic acid (189), which at room temperature cyclize spontaneously to phenanthridone and dibenz[f>,d]azepin-6-one (190) respectively (61JOC1329). The hydrogen bromide-induced cyclization of dinitriles (Scheme 16) is adaptable to the synthesis of 2-amino-7-bromo-3//-azepines and 5H-dibenz[c,e]azepin-7-ones (67JOC3325). Apparently, for unsymmetrical dinitriles cyclization is such as always to give the azepine with the bromo substituent attached to the carbon of the a,j8-unsaturated nitrile as exemplified in Scheme 16. 

The synthetic protocols used for the preparation of oligonucleotides on supports can also be used to prepare oligomers from diols other than nucleosides. Symmetric or unsymmetric diols, such as N-acylated 4-hydroxyprolinol [268] or cyclopentane-derived diols (carbocyclic deoxyribose analogs [269]), can be selectively mono-trity-lated and then converted into a phosphoramidite that is suitable for the solid-phase synthesis of oligophosphates. An illustrative synthesis of protected //-phosphonates from diols, as well as their conversion on CPG into oligomeric phosphoramidates, are outlined in Figure 16.28. 

The synthesis of both symmetrically and unsymmetrically substituted organopolysilanes is achieved in analogous fashion to that of permethylated polysilanes. Some examples are given below. 

A cyclodimerization, analogous to that of methyl anthranilate, was exhibited by 2-aminothiophenes bearing a carboxylic portion in position 3 to give the dithienodiazocines. In that patent, the procedures for the synthesis of unsymmetrical dithienodiazocines, thienobenzodiazocines and tetracyclic diazocines were also described <2004W0010136>. 

Flavins (8), 8-azaflavin (9) and their analogs are characteristic oxidants toward thiols under anaerobic and other specific conditions (equation 12). S-Arylidene-l,3-dimethylbarbituric acid derivatives (10) also work as the oxidant in dioxane at 12(X-1S0 C, and the method was applied to synthesis of unsymmetrical disulfides. Electrochemical oxidation and photolysis of thiols to disulfidqs are also known. 

In the presence of sodium hydroxide, thiols react with alkyl halides to form the sulfides (20) the reaction occurs via the sodium thiolate and is analogous to the well-known Williamson synthesis of ethers and can also be applied to obtain unsymmetrical sulfides (Scheme 18). Symmetrical sulfides may be prepared directly by condensation of sodium sulfide with alkyl halides (Scheme 18). These reactions are of the SN2 type, and consequently the optimum yields of sulfides are realised using primary alkyl halides. 

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