Unsaturated substrates reactions

Ritleng, V., Sirlin, C. and Pfeffer, M. (2002) Ru-, Rh-, and Pd-catalyzed C-C bond formation involving C—H activation and addition on unsaturated substrates reactions and mechanistic aspects. Chem. Rev., 102, 1731. 

Ruthenium, Rhodium, and Palladium-Catalyzed Carbon-Carbon Bond Formation Involving C-H Activation and Addition on Unsaturated Substrates Reactions and Mechanistic Aspects ... 

Gycloaddition Reactions. Isocyanates undergo cyclo additions across the carbon—nitrogen double bond with a variety of unsaturated substrates. Addition across the C=0 bond is less common. The propensity of isocyanates to undergo cycli2ation reactions has been widely explored for the synthesis of heterocycHc systems. Substrates with C=0, C=N, C=S, and C=C bonds have been found to yield either 2 + 2, 2 + 2 + 2, or 2 + 4 cycloadducts or a variety of secondary reaction products (2). 

Both the Wolff-Kishner and Clemmensen reductions of a, -unsaturated ketones give olefins. There has been considerable confusion concerning the exact product composition in the case of A -3-ketones. Wolff-Kishner reduction gives A" -, 5a-A - and 5 -A -olefins, and, depending on the substrate reaction conditions and work-up, any one or more of these may be isolated. (See ref. 287 for a recent review of the Wolff-Kishner reduction.)... 

Synthetic polymers are classified by their method of synthesis as either chain-growth or step-growth. The categories ate somewhat imprecise but nevertheless provide a useful distinction. Chain-growth polymers are produced by chain-reaction polymerization in which an initiator adds to a carbon-carbon double bond of an unsaturated substrate (a vinyl monomer) to yield a reactive inter-... 

Cyanoisopropyl radicals generally show a high degree of specificity in reactions with unsaturated substrates. They react with most monomers (c.g. S, MMA) exclusively by tail addition (Scheme 3.4). However, Bcvington et al.11 indicated that cyanoisopropyl radicals give ca 10% head addition with VAc at 60 °C and that the proportion of head addition increases with increasing temperature. 

Hydroxy radical and sulfate radical anion, though they may sometimes give rise to similar products, show quite different selectivity in their reactions with unsaturated substrates. In particular, the sulfate radical anion has a somewhat lower propensity for hydrogen abstraction than the hydroxyl radical. For example, the sulfate radical anion shows little tendency to abstract hydrogen from mcthacrylic acid.232... 

The cydopropanation reaction of an unsaturated substrate is one of the most important strategies to access three-membered ring derivatives. The use of Fischer carbene complexes to perform this kind of cyclisation has become an important tool in organic synthesis [4]. In the next few sections the most significant features of this chemistry are briefly described. 

Scheme 10 Reactions of FeXs with different unsaturated substrates...

Because organophosphorus compounds are important in the chemical industry and in biology, many methods have been developed for their synthesis [1]. This chapter reviews the formation of phosphorus-carbon (P-C) bonds by the metal-catalyzed addition of phosphorus-hydrogen (P-H) bonds to unsaturated substrates, such as alkenes, alkynes, aldehydes, and imines. Section 5.2 covers reactions of P(lll) substrates (hydrophosphination), and Section 5.3 describes P(V) chemistry (hydrophosphorylation, hydrophosphinylation, hydrophosphonylation). Scheme 5-1 shows some examples of these catalytic reactions. 

The reaction of P-H bonds with unsaturated substrates often proceeds without a metal catalyst [2]. In addition, add or base-catalyzed [3] as well as radical reactions [4] have been reported and extensively reviewed. Metal-catalyzed transformations like the ones described here, however, often offer improvements in rate, selectivity,... 

Metal-catalyzed additions of P(III)-H and P(V)-H bonds to unsaturated substrates have been studied much less than related additions of, for example, B-H or Si-H bonds [36]. Already, some synthetically useful processes have been developed, and further work is likely to produce additional useful transformations as well as more fundamental information on the mechanisms of these reactions. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Alternatively, l,3-dithiol-2-ones have been obtained by reacting di-isopropylxanthogen disulfide with unsaturated substrates, such as disubstituted alkynes R2C2, in the presence of AIBN (azoisobutyrylnitrile), a radical initiator.78 Finally, vinylene dithiocarbonates can be obtained by reacting mer-cury(II) acetate with the corresponding trithiocarbonates, generated by reaction of electrophilic alkynes with ethylene trithiocarbonate.79 Analogously,... 

In this review, an attempt is made to exhaustively catalog the rapidly growing subset of metal-catalyzed reductive C-C bond formations comprising the hydrometallative and hydrogenative carbocyclization of 7t-unsaturated substrates, and application of these methods in target-oriented synthesis. Content is organized on the basis of reaction... 

Products of catalytic RCM were formerly not attainable by any other means, or in such a selective and efficient manner. With these unsaturated substrates easily accessible, myriad reaction technologies have emerged that involve the regio - and stereoselective functionalization of such adducts. In the absence of catalytic RCM, these processes would either remain undeveloped or would be, for the most part, categorized as interesting but unpractical methods in synthesis. 

The success of stoichiometric ionic hydrogenations is due to achieving a fine balance that favors the intended reactivity rather than any of several possible alternative reactions. The acid must be strong enough to protonate the unsaturated substrate, yet the reaction of the acid and the hydride should avoid producing H2 too quickly under the reaction conditions. The commonly used pair of CF3C02H and HSiEt3 meets all these criteria. 

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