Unactivated alkenes, allylation

Reactions of this type are mostly performed with internal nucleophiles attached to the carbon atom adjacent to the iminium nitrogen, thus leading to tropane-like azabicyclic systems. Both allyl- and propargylsilanes, activated and unactivated alkenes, and ketones have been successfully used as nucleophiles. The products 1 and 2 are also obtained via two consecutive C —C bond-forming reactions in a single operation. 

In general, transition metal-catalyzed addition reactions to 1,3-dienes gave 1,4-adducts via 7t-allyl metal intermediates.23 The ar //-Markovnikov 1,2-addition mode of this reaction is therefore unusual (Scheme 17). It was noted that the configuration of the 3-olefin was retained with either ( )- or (Z)-1,3-dienes. The observation that the 3-olefin was unimportant for this reaction strongly suggests that the method could be applicable to unactivated alkenes. 

Phenylacetonitriles can be induced to undergo Michael reactions with unactivated alkenes. For example, propenylarenes, formed in situ from allylarenes, react with phenylacetonitriles to form 3-aryl-l-cyano-2-methyl-l-phenylpropanes (70-98%) [3] by a procedure analogous to 6.4.1.B, Similarly, the nitriles react with alkynes giving allyl cyanides (80-95%) [38]. 

Certain hindered alkenes display exceptional behavior. They readily undergo cycloaddition to yield 1,2-dioxetanes despite the presence of allylic hydrogen. The oxidation of 2,2 -biadamantylidene was the first successful synthesis of the dioxetane of an unactivated alkene 400,401... 

Copper-catalyzed allylic oxidation allows the functionalization of unactivated alkenes into chiral allylic carboxylates.1347 The use of oxazoline-containing ligands give good enantioselectivities, but the reaction is extremely slow.1348-1351 Chiral bipyridine complexes, in turn, are much more active and give products in good yields and enantioselectivities up to 70% when applied in benzoyloxylation of cycloalkenes with rm-butyl perbenzoate.1352,1353... 

Acetoxylation of alkenes takes place in allylic position [40,115], concurrent with addition of acetoxy groups across the double bond or double-bond system. The mechanism is almost certainly analogous to that discussed previously for methoxylation [Eq. (20)]. Because AcO is difficult to oxidize, the anodic discharge of simple, unactivated alkenes may be achieved in its presence. Subsequent reactions of the cationic intermediates are not very selective, but several experimental parameters may be controlled and the method can compare well with the few competing chemical methods. 

Very recently, Liu and coworkers reported a palladium-catalyzed intramolecular aerobic oxidative allylic amination of unactivated alkenes [34]. The reaction of 22... 

Paderes and Chemler developed an intramolecular diastereoselective aminooxygenation of unactivated alkenes to pyrrolidines. Cu(EH)2/02 catalytic system could lead to 2,5-cis- and 2,5-fra s-pyrrolidines formation from a-substituted 4-pentenylsulfonamides in good to excellent yields and >20 1 selectivity. For P- and /-substituted 4-pentenylsulfonamides, Cu(OTf)2-bis(oxazoline) with O2 catalytic system could give higher diastereoselectivities. Furthermore, enantioselective desymmetrization could be achieved (up to 98% ee) with /l-allyl-4-pentenylsulfonamide [26] (Scheme 8.13). 

The Influence of Dienophile Structure on Reactivity and Stereoselectivity in [4+2] Cycloadditions of Nitroalkenes Various dienophiles have been used successfully in nitroalkene [4 + 2] cycloadditions, such as vinyl ethers [77], enamines [78], ketene acetals [79], unactivated alkenes [58, 80, 81], 1,3-dienes [47, 82], allylic silanes [83], and allenes [84] (Scheme 16.10). Because of their high... 

In analogy with the enantioselective carbonyl-ene reactions (Chapter 2, Section 2.11), an attractive but much less well precedented alternative to imine allylations is enantioselective imino-ene reactions. The first such example was reported by Lectka, who found that the Tol-BINAP copper complex 216 promoted the addition of unactivated alkenes to N-tosyl imine 110 (Equation 27) [31, 153, 173]. This transformation provided the homoallylic a-amino acid 270 in 90 % yield and 99 % ee. 

Diacetoxyiodo)benzene in the presence of tert-butyl hydroperoxide readily oxidizes alkenes at the allylic position (Scheme 3.88) [269]. This reaction proceeds via initial formation of the tert-butylperoxy radical and it can be extended to the oxidation of unactivated C—H bonds in alkyl esters and amides to give the corresponding keto compounds under mild conditions [270]. 

The highly reactive allyl-iron hydride [HFe(CO)3(T 3-CH2CHCH2)], first proposed over 30 years ago as a key intermediate in the [Fe(CO)s]-catalysed isomerisation of alkenes, has been characterised by NMR spectroscopy for the first time53. A procedure has been reported for the synthesis of tetrahydrofuran esters based on a formal [3 + 2] cycloaddition reaction of [CpFefii -C3H5)(CXD)2] with unactivated carbonyl compounds. 

Evidence has been obtained for palladacycles being catalyst precursors for soluble Pd(0) species and/or Pd nanoparticles.Palladacyles have been successfully employed as catalysts for alternating CO/alkene copo-lymerization. They have been amenable to allylic substitution,to oxygenation of unactivated sp C-H bonds,to allylic imidate rearrangement," " " " and to oxidation of alcohols to aldehydes and ketones." " ... 

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