Alkynes diimide

Dia ene deductions. Olefins, acetylenes, and azo-compounds are reduced by hydrazine in the presence of an oxidizing agent. Stereochemical studies of alkene and alkyne reductions suggest that hydrazine is partially oxidized to the transient diazene [3618-05-1] (diimide, diimine) (9) and that the cis-isomer of diazene is the actual hydrogenating agent, acting by a concerted attack on the unsaturated bond ... 

Figure 5.1. Reduction of Wang resin bound alkenes and alkynes with diimide (HN=NH) [6].

The other well-known type of group transfer reaction is represented by the concerted syn delivery of two hydrogen atoms from the reactive intermediate diimide 1.25 to an alkene or alkyne, driven by the formation of the stable molecule nitrogen. 

As regards the protecting effect, the complex is stable to Lewis acids. Also, no addition of BH3 occurs. As Co2(CO)6 can not coordinate to alkene bonds, selective protection of the triple bond in enyne 137 is possible, and hydroboration or diimide reduction of the double bond can be carried out without attacking the protected alkyne bond to give 138 and 139 [32], Although diphenylacetylene cannot be subjected to smooth Friedcl Crafts reaction on benzene rings, facile /7-acylation of the protected diphenylacetylene 140 can be carried out to give 141 [33], The deprotection can be effected easily by oxidation of coordinated low-valent Co to Co(III), which has no ability to coordinate to alkynes, with CAN, Fe(III) salts, amine /V-oxidc or iodine. 

Reduction of alkenes and alkynes with diimides is also an example of an ene reaction. 

Like the double bond, the carbon-carbon triple bond is susceptible to many of the common addition reactions. In some cases, such as reduction, hydroboration and acid-catalyzed hydration, it is even more reactive. A very efficient method for the protection of the triple bond is found in the alkynedicobalt hexacarbonyl complexes (.e.g. 117 and 118), readily formed by the reaction of the respective alkyne with dicobalt octacarbonyl. In eneynes this complexation is specific for the triple bond. The remaining alkenes can be reduced with diimide or borane as is illustrated for the ethynylation product (116) of 5-dehydro androsterone in Scheme 107. Alkynic alkenes and alcohols complexed in this way show an increased structural stability. This has been used for the construction of a variety of substituted alkynic compounds uncontaminated by allenic isomers (Scheme 107) and in syntheses of insect pheromones. From the protecting cobalt clusters, the parent alkynes can easily be regenerated by treatment with iron(III) nitrate, ammonium cerium nitrate or trimethylamine A -oxide. ° ... 

The commonest example of. v>w-addition is the heterogeneously catalysed hydrogenation of an alkene, using either Ni, Pt or Pd, or in the case of the reduction from an alkyne to an alkene, using the Lindlar catalyst. The reduction of an alkene can also be achieved using diimide. 

Prepared by hydrolysis of the anthracene —diethyl azodicarboxylate and decarboxylation, the reagent decomposes in refluxing ethanol to anthracene and diimide, When taken in 2-8 fold excess, it reduces azobenzene and reactive alkenes and alkynes. 

Diimide, HN=NH. The reagent, generated in situ by cupric ion-catalyzed oxidation of hydrazine with oxygen (air), hydrogen peroxide, potassium ferricyanide, or mercuric oxide, reduces olefins, alkynes, and azo compounds. Reduction of the... 

Of the various 16-hydroxy analogs clearly the most interesting were the 16-methyl derivatives, and further development of this series was undertaken (55). Among the analogs prepared were compounds featuring a 13-cis double bond (Scheme 33), the vinyl iodide for which was obtained vm diimide reduction (22) of the 1-iodo-l-alkyne 199, a 17-trans double bond (203, Scheme 33)... 

Hydrazine is oxidized by PhI(OAc)2 to diimide, which may be used to reduce alkenes and alkynes under mild conditions (Table 2). ... 

A well-known example of group transfer reaction with p = 0, q = 2 is represented by the concerted reduction of alkenes and alkynes with the reactive intermediate diimide stereoselectively in the cis fashion (Scheme 6.2). The driving force of the reaction is the formation of the stable nitrogen molecule. 

Again, as seen with alkenes, both borane (B2H6) (Equation 6.22) and diimide (H-N=N-H) (Scheme 6.15) can be used to reduce alkynes. Indeed, the reaction of internal alkynes with borane is apparently more facile than that with the alkene that results from consummation of the reduction. Further, as would be expected, suprafacial addition of hydrogen and boron obtains and Z- (or cis-) alkene is the only product. The use of deuterated boron compounds (e.g., the hindered 9- H-9-borabicyclo[3.3.1]nonane [9- H-9-BBN]), commercially viable since it contains only one deuterium ( H), followed by use of deuterated acetic acid (CH3C02, i.e., reductive workup) produces Z- (or cw-)-dideuteroalkene of high stereospecificity and in high yield (Scheme 6.65). 

A synthesis of the biaryl moiety and the seven-membered ring core 3.16 of allocolchicine employed a C-H activation reaction as part of the intramolecular biaryl formation (Scheme 3.19). The starting material was prepared by the acid chloride variant of the Sonogashira reaction (Section 2.8), coupling alkyne 3.17 with acid chloride 3.18. Asymmetric reduction of the ketone 3.19, protection of the alcohol and reduction of the alkyne gave the substrate 3.20 for CH activation. Diimide, generated in situ, was employed for the alkyne reduction to avoid potential problems of over reduction. C-H activation and biaryl formation was then... 

Another type of group transfer reaction is the transfer of hydrogens from diimide to an alkene or alkyne. 

Diimide reduction of alkenes and alk3mes are also group transfer reactions. Delivery of two hydrogen atoms to an alkyne or alkene takes place in a concerted process involving suprafacial delivery of two hydrogens in a TS. These reactions are per-icyclic in nature. 

A multi-component reaction of a terminal alkyne, sulfur, electrophile (E-X) and carbodiimides, R R CH-N=C=N-R, produces 1,2-dihydrothiopyrimidines and 2,3-dihydropyrimidinthiones (43, R" derived from alkyne, E = H, alkyl). The expected N=C cleavage of the diimide is accompanied by an unexpected C(5p )-H cleavage, such that the carbodiimide acts as sources of H -I- R R -C-N -I- C=N-R , with subsequent reorganization to give products. 

Starting from a 1 2 mixture of an electron-rich bis-l,5-(dinaphtho)-38-crown-10 and the electron-poor bis-acetylenic compound 1, Sanders used the template effect obtained by the inclusion of the pyromellitic diimide 1 in the crown ether to direct the oxidative coupling of the terminal alkynes toward the formation of the cyclized structure, the [2]catenane, with a 38% chemical yield. When 1 was replaced by a more electron-poor moiety obtained from 1,4,5,8-naphthalene tetracarboxylic diimide (2, Scheme 17.5) the yield of the catenane improved to 52%. 

Exocyclic bis-silylated olefins have been constructed through the Pd(OAc)2-catalyzed reaction of alkynes with a tethered disi-lanyl group. The reactions are carried out in the presence of a tert-alkyl isocyanide, although the precise role of this ligand is unclear. Diimide reduction of the disilylated alkene so-formed followed by Fleming-Tamao-type oxidation of the two C-Si bonds in the saturated product then affords 1,2,4-triols in a stereoselective manner (eq 83).l ... 

Similarly, selective insertion of a C=N double bond of iV,A -diisopropylcarbo-diimide was also observed to afford the complex 3-8 in 86 % isolated yield [21]. In addition to the above C=0 and C=N double bond insertion reactions, the C=C triple bond of alkynes was also found to react smoothly and selectively with the... 

Cyclopentadienylcobalt complexes are also good for co-cyclotrimerization of alkynes with other unsaturated compounds containing the carbon-heteroatom double bonds, especially when they are part of the cumulene system such as isocyanates, diimides, and carbon dioxide. The reaction conditions are essentially the same as in the previously mentioned processes. However, the biggest problem remains the selectivity for the formation of heterocycles, because of the strong competition for the formation of benzene derivatives. Whereas co-cyclotrimerization of diimides and isocyanates results in the formation of reasonable yields of the corresponding heterocycles 170 and 171 (Scheme 75), in the case of carbon dioxide the yields are generally low [108, 109]. Recently, it has been shown that the ruthenium complex 106 is capable of efficient catalysis of co-cyclotrimerization of diynes and isocyanates [110] and isothiocyanates [111] under mild reaction conditions. 

---