Hydrides reactions, with unsaturated organic compounds

Organolead derivatives prepared in recent years by one or more of the above reactions are the azides 208>, cyanides 123>, fulminates 45>, arsinates 171), sulfides 104>, alkoxides 242>, peroxides 263>, amines 231>, and phosphines, arsines, and stibines 280-281) The alkoxide 105>, hydride 231> and amine 231> derivatives of organolead undergo reaction with various unsaturated organic compounds to form novel organolead compounds, many of which are not synthesizable by other methods. 

M is an unsaturated hydrocarbon or an organic compound such as CH3OH, CH3I, CH3N02, (CH3)2CO, CH3NH2, etc. When M is an olefin, Reaction 27 or 28 will compete with a hydride transfer process (see earlier discussion) and a condensation process. For instance, in the radiolysis of C3D8-CH3CHCH2 mixtures (9), the relative rates of Reactions 29, 30, 31, and 32... 

A delocalized 0-stannyl radical anion can also be generated from the reaction of an a,/ -unsaturated ketone or aldehyde with tributyltin hydride and radical initiator AIBN [3, 4, 5a, 5b]. Thus, a,/ -unsaturated carbonyl compound 4 (R or R = H or alkyl), can be reacted with wBu SnH under standard free-radical conditions to give allylic O-stannyl ketyl species (5 6), shown in Scheme 2. After hydrogen atom transfer to the -position of 6, a synthetically useful tin(IV) enolate is produced [5b, 5d, 5g. Allylic 0-stannyl ketyls have both one- (radical) and two-electron (anionic) sites for reactivity. These reactions can proceed in a sequential manner - a rapidly-evolving methodology in organic synthesis [2, 5, 8j. If the one-electron reactivity in 6 is used with a radicophile, then the tin enolate or two-electron reactivity can be used in reactions with suitable electrophiles (E ). Note that the carbonyl species. 

The formal conjugate addition of a hydride to a,f(-unsaturated carbonyl compounds with a subsequent aldol reaction of the in situ formed enolate has been frequently employed in organic synthesis. A broad range of procedures have been developed using various metals (e.g., rhodium, cobalt, iridium, mthenium, copper) and different reductants (typically silanes, boranes, or elemental hydrogen) [37]. 

A quite new class of catalysts based on early main group metals (Ca, Sr, and K) was recently reported to promote general conversion of conjugated double bond (137). The catalytic reaction is initiated by the formation of a highly reactive metal hydride that adds either to an alkene or to a silane. The regiochemistry for the hydrosilylation of 1,1-diphenylethylene (DPE) catalyzed by calcium complex can be completely controlled by the polarity of the solvent. Amine borane and phosphine borane complexes were successfully used as effective catalysts for hydrosilylation of organic compounds with internal unsaturated bond (138) that cannot be selectively hydrosilylated in the presence of Pt catalysts. 

In all reactions discnssed in the two preceding paragraphs, an unsaturated organic palladium species was acting as the electrophilic mediator of the cyclization process. A Pd-mediated cyclization initiated by a palladium(II) hydride species was also developed on w-unsatnrated /3-dicarbonyl compounds. In this way, 5-acetylenic potassinm enolates, generated from the reaction of compounds of type 32 with potassium t-butoxide, smoothly underwent cyclization when treated with a palladium(O) complex in THF. This led to the formation of methylenecyclopentanes 54 or unsaturated esters 55, depending on the reaction conditions, and particularly on the amount (stoichiometric or catalytic) of potassium l-butoxide (Table... 

The aim of this chapter is to examine the application of well-defined N-heterocyclic carbene (NHC) complexes, as well as the systems prepared in situ which involve free NHCs or the precursor salt, for the reduction of unsaturated organic molecules such as alkynes, alkenes and carbonyl compounds. The most active complexes for such reactions are based on electron-rich, late transition metals in low oxidation states. Herein, reductions useful for organic synthesis will be classified into four types according to the hydride source used (i) hydrogenations, (ii) transfer hydrogenation, (iii) hydrosilylation and (iv) hydroboration. For examples of reduction reactions with systems containing non-classical NHC ligands, the reader is referred to Chapter 5. 

Fig. (2). The cyclization of enone (9), gives origin of two Cyclized products (10) and (11). Ketone (10), Ketone (10) is converted to the saturated ketone (14)under standard organic reactions.Bromination and dehydrobromination of ketone (14) yields the a,P-unsaturated ketone (IS), which on subjection to catalytic hydrogenation affords (16) and this on reduction, produces alcohol (17). The compound (13) yields (18) by standard reactions that are used for the transformation of (12) to (16). Reduction with metal hydride followed by oxidation affords ketone (11), which is converted to alcohol (17)...

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