Alkenes reaction with diimide

In agreement with this mechanism is the fact that the stereochemistry of addition is syn.44 The rate of reaction with diimide is influenced by torsional and angle strain in the alkene. More strained double bonds react at accelerated rates.45 For example, the more strained trans double bond is selectively reduced in Z,K-1,5-cyclodecadiene. 

Several 1,2,4-trioxolanes are known which contain a double bond linked in some way to the ring, with interest focusing on furan endoperoxides. The alkene moiety of 2,5-dimethylfuran endoperoxide (41) can be selectively functionalized in the presence of the 1,2,4-trioxolane ring. Reaction with diimide gives the saturated ozonide <81TL3509> and a single addition product was obtained with p-nitrophenylazide, although the stereochemistry of the reaction was not determined. 

Terminal acetylenes are selectively hydrogenated to alkenes in the presence of the iron(II) precursors [P(CH2CH2PPh3) FeH(X2) BPh4] (X = N or H) under mild conditions in THF. Cw-Addition of hydrogen to 1-iodoalkynes is brought about by reaction with diimide, N2H2. ... 

A further difference to electrophilic alkenes shown by DAD and other diimides is that tertiary amines, such as A-cyclohexylpyrrolidine (167), are dehydrogenated to the enamine. Further reaction then occurs to give the product of 2,6-disubstitution (168)352. Diacyl diimides, such as dibenzoyldiimide (DBD), are even more remarkable. The action of DBD on 167 at room temperature results in dehydrogenation of the pyrrolidine ring and reaction with a further two equivalents of DBD to give 169353 (Scheme 178). 

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. ° ... 

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. 

Alkyl-5-alkyliminothiatriazolines (50) decompose slowly around 40-60 "C and rapidly at 125°C with formation of sulfur, nitrogen, and carbodiimide (51) (Equation (4)). However, the carbo-diimides (51) formed react with undecomposed thiatriazoline (50), which in part explains the low yields of isolable carbodiimide. It has not been possible by trapping experiments to decide whether the decomposition involves an intermediate as addition of electron-rich alkenes or heterocumulenes induces immediate nitrogen evolution in a bimolecular reaction (see Section 4.19.5.2) <78JCS(P1)1440>. 

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. 

The desulfurization of episulfides by d.v-oxaziridine (56) appears to be a general reaction affording the alkene, dimethylsulfur diimide (MeN=S=NMe), and azomethane (MeN=NMe) (80JOC1691). These latter products are formed via the intermediate thionitrosomethane (59) (Equation (8)) which was trapped with 2,3-butadiene to give the cyclic sulfenamide (60) in 22-33% yield. The alkenes are formed in good to excellent yield (80-90%) with retention of configuration. 

Alder Ene Reactions. Like the Diels-Alder reaction, Alder ene reactions usually take place only when the enophile has a Z-substituent, the regiochemistry is that expected from the interaction of the HOMO of the ene and the LUMO of the enophile, and Lewis acids increase the rate. All these points can be seen in the reaction of T-pinene 6.449 with the moderately activated enophile methyl acrylate, which takes place at room temperature in the presence of aluminium chloride,928 but which would not have taken place easily without the Lewis acid. The lowering of the LUMO energy of the methyl acrylate accounts for the increase in the rate of reaction. Similarly, the rates of diimide reductions of alkenes show some correlation with ionisation potential and hence orbital properties.929... 

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). 

In a typical reaction a concentrated solution of polymer in a solvent such as diglyme is heated with an excess of p-toluene sulphonyl hydrazide. The diimide is generated in situ to react with the alkene as indicated in the following scheme ... 

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 ... 

Reduction of tosylhydrazones of a,/3-unsaturated ketones gives alkenes with the double bond being located between the former carbonyl and a-carbon atoms. This reaction is believed to proceed via an initial conjugate reduction followed by decomposition of the resulting vinylhydrazine to a vinyl diimide. 

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