Organic synthesis nitro olefins

The reaction presented in Scheme 3.38 is involved in the novel [4+ 2] [3+ 2] tandem strategy for the use of nitroalkenes (42) in target organic synthesis (for details, see Section 3.4.4). Taking into account the great contribution of Prof. S. Denmark the in investigation of different aspects of this strategy, the latter can be classified as Denmark s approach. The principal aspects of [4+ 2]-cyclo-addition of nitro olefins were summarized in two fine reviews (99, 100). 

Aliphatic nitro compounds are versatile building blocks and intermediates in organic synthesis,14 15 cf. the overview given in the Organic Syntheses preparation of nitroacetaldehyde diethyl acetal.16 For example, Henry and Michael additions, respectively, lead to 1,2- and 1,4-difunctionalized derivatives.14 18 1,3-Difunctional compounds, such as amino alcohols or aldols are accessible from primary nitroalkanes by dehydration/1,3-dipolar nitrile oxide cycloaddition with olefins (Mukaiyama reaction),19 followed by ring cleavage of intermediate isoxazolines by reduction or reduction/hydrolysis.20 21... 

Nitro olefins are useful intermediates in organic synthesis. Conjugated nitroalkenes are excellent acceptors (Michael reaction and Diels-Alder cycloaddition) and the nitro group can be further transformed, in situ, into several reactive intermediates. 

Ru(CO)5 is less frequently used than Fe(CO)5 for organic synthesis or as a starting material as a zero-valent ruthenium complex because of its ease of decomposition to Ru4(CO),2 [99]. Dodecacarbonyltriruthenium is very useful for these purposes. It has been showm to be an active catalyst for the hydrogenation of olefins [100], carbonyla-tion of ethylene [101], hydroformylation of alkenes [102], water-gas shift reaction [103], and reduction of nitro groups [104], and recently, C—H bond activation [105] and coupling of diynes with CO [106]. 

Nitro-olefins are versatile reagents in organic synthesis, as reflected by the diversity of ways in which they have been used." As Michael acceptors nitro-olefins react with alkoxy-enolates," dimedone under KF catalysis, and benzyl mercaptan. Nitroethylene itself has now also been shown to be a stable and reactive reagent for organic synthesis, undergoing cycloaddition, Michael, and ene reactions. 

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