Allyl-substrate-controlled stereoselective

Roush and coworkers expanded the scope of this reagent 18 for the double aUylation of carbonyl compounds. As expected, the first allylation (170) showed reagent-controUed anti-diastereoselec-tion and the second allylation (172) proceeded via substrate-controlled stereoselection to produce optically active ( )-pent-2-ene-l,5-diols (E)-173 in high yields (Schane 25.24). They further noted that the increase of bulk on boronate ring led to the formation of the corresponding (Z)-173 Z-diols as single isomers upon oxidative woikup (Scheme 25.25). 

Even though Ni(CO)4 is called liquid death, this nickel catalyst has been applied in carbonylation reactions [52]. The group of Ricart reported a nickel-catalyzed carbonylative cycloaddition of alkynes and aUyl hahdes to cyclopentanes. The desired products were obtained in high yields and with controlled stereoselectivity. Iron was used as a reductant. An extension of the reaction to new substrates led to the conclusion that, although the steric and electronic effects of the alkyne substituents are generally irrelevant in relation to the adducts and their yields, those of the allylic counterpart may have a significant influence on the outcome of the reaction. However, the presence of the amine moiety in the alkyne completely inhibited the reaction. The feasibility of a multicentered reaction was verified with a triacetylene, in which up to 12 bonds were created simultaneously and in good yield (Scheme 1.30). 

As shown in Scheme 14.9a,b, an efficient protocol for the stereoselective synthesis of 1,3-syn and -anti tetrahydropyrimidinones (syn- and anti- 2) could be developed [13]. The modular procedure is based on a stereodivergent cycliza-tion of readily available urea-type substrates 41 by intramolecular allylic substitution. The cychzation proceeds with excellent yield (up to 99%) and selectivity (up to dr > 20 1), purely based on substrate control. The product pyrimidines 42 can be readily transformed into the corresponding free syn- and anti-amines 43. Furthermore, also a novel domino sequence for the rapid assembly of 1,3-syn-substituted oxazines 46 could be realized [14]. Mechanistically, the one-pot procedure is based on a three-step sequential process involving a hemi-aminalization... 

An interesting way to control the stereoselectivity of metathesis-reactions is by intramolecular H-bonding between the chlorine ligands at the Ru-centre and an OH-moiety in the substrate [167]. With this concept and enantiomerically enriched allylic alcohols as substrates, the use of an achiral Ru-NHC complex can result in high diastereoselectivities like in the ROCM of 111-112 (Scheme 3.18). If non-H-bonding substrates are used, the selectivity not only decreases but proceeds in the opposite sense (product 113 and 114). 

An asymmetric version of aminoallylation has been developed via a transfer aminoallylation protocol. This methodology involves the initial aminoallylation of camphorquinone 207 with 5-allylpinacol boronate 177 in alcoholic ammonia, furnishing the a-aminoketone 208 stereoselectively, which upon treatment with an aldehyde 209 and achiral allyl boronate 177 leads to the in situ formation of chiral imine 210 followed by allylation to yield the homoallylic amines 212 (Scheme 35) <2006JA11038>. Excellent levels of enantio- and diastereo control were observed for the allylation of a wide array of aldehyde substrates. 

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