Allylation reactions catalytic allylic

The intermediate 190 of the intramolecular aminopalladation of an allenic bond with jV-tosylcarbamate undergoes insertion of allylic chloride. Subsequent elimination of PdCl2 occurs to afford the 1,4-diene system 191. The regeneration of Pd(II) species makes the reaction catalytic without using a reoxidant[190]. 

Several Pd(0) complexes are effective catalysts of a variety of reactions, and these catalytic reactions are particularly useful because they are catalytic without adding other oxidants and proceed with catalytic amounts of expensive Pd compounds. These reactions are treated in this chapter. Among many substrates used for the catalytic reactions, organic halides and allylic esters are two of the most widely used, and they undergo facile oxidative additions to Pd(0) to form complexes which have o-Pd—C bonds. These intermediate complexes undergo several different transformations. Regeneration of Pd(0) species in the final step makes the reaction catalytic. These reactions of organic halides except allylic halides are treated in Section 1 and the reactions of various allylic compounds are surveyed in Section 2. Catalytic reactions of dienes, alkynes. and alkenes are treated in other sections. These reactions offer unique methods for carbon-carbon bond formation, which are impossible by other means. 

In addition, a catalytic version of Tt-allylpalladium chemistry has been devel-oped[6,7]. Formation of the Tr-allylpalladium complexes by the oxidative addition of various allylic compounds to Pd(0) and subsequent reaction of the complex with soft carbon nucleophiles are the basis of catalytic allylation. After the reaction, Pd(0) is reformed, and undergoes oxidative addition to the allylic compounds again, making the reaction catalytic.-In addition to the soft carbon nucleophiles, hard carbon nucleophiles of organometallic compounds of main group metals are allylated with 7r-allylpalladium complexes. The reaction proceeds via transmetallation. These catalytic reactions are treated in this chapter. 

PdCb, and the allylated lactone 232 is formed. Regeneration ofPdCl2 as shown by 231 makes the reaction catalytic. In this reaction, use of the Li salt 227 of 4-pentynoic acid (223) is recommended. Reaction of lithium 3-octynoate (233) with allyl chloride affords the unsaturated lactone 234, which is converted into the 7-keto acid 235 by hydrolysis[126]. 

Allyl complexes of some other transition metals, such as Ru, Fe, Cr and Ti, are also used for synthetic purposes. Reaction of allylic acetates with aldehydes catalyzed by a Ru complex in the presence of Et3N and CO gives the alcohol 39. It seems likely that the reaction itself is stoichiometric. But a high-valent Ru complex, formed by the reaction with the electrophile, is reduced to a lower valences with Et3N or CO, making whole reaction catalytic [2,13],... 

M. Lautens, Science of Synthesis , Georg Thieme Verlag, New York, 2001, Vol. 1, p. 11 E. Negishi, Handbook of Organopalladium Chemistry for Organic Synthesis , Wiley-Interscience, New-York, 2002, Version 2 B. M. Trost and M. L. Crawley, Chem. Rev., 2003, 103, 2921 B. M. Trost and C. Lee, Asymmetric Allylic Alkyaltion Reactions, Catalytic Asymmetric Synthesis , Wiley-VCH, 2000, p. 593 A. Pfaltz and M. Lautens, Allylic Substitution Reactions, Comprehensive Catalysis I-IIF, Springer, 1999, Vol. 2, p. 833. 

Trost, B. M., and T. R. Verhoeven New Synthetic Reactions. Catalytic vs. Stoichiometric Allylic Alkylation. Stereocontrolled Approach to Steroid Side Chain. J. Amer. Chem. Soc. 98, 630 (1976). 

In addition to the above-mentioned allylic alkylation reactions, catalytic-in-copper C(sp )-C(sp ) cross-coupling reactions with alkylzincs can be achieved with some other specific electrophiles. For instance, the benzylzinc reagent 127, prepared in the presence of LiCl, undergoes coupling with the benzyl bromide 128 in the presence of only 0.4mol% CuCN-2 LiCl, with a yield of 89% (Scheme 4.29) [112, 113]. 

Organometallic Compounds and Catalysis The Heck Reaction Catalytic Allylic Alkylation... 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

TT-Aliylpalladium chloride reacts with a soft carbon nucleophile such as mal-onate and acetoacetate in DMSO as a coordinating solvent, and facile carbon-carbon bond formation takes place[l2,265], This reaction constitutes the basis of both stoichiometric and catalytic 7r-allylpalladium chemistry. Depending on the way in which 7r-allylpalladium complexes are prepared, the reaction becomes stoichiometric or catalytic. Preparation of the 7r-allylpalladium complexes 298 by the oxidative addition of Pd(0) to various allylic compounds (esters, carbonates etc.), and their reactions with nucleophiles, are catalytic, because Pd(0) is regenerated after the reaction with the nucleophile, and reacts again with allylic compounds. These catalytic reactions are treated in Chapter 4, Section 2. On the other hand, the preparation of the 7r-allyl complexes 299 from alkenes requires Pd(II) salts. The subsequent reaction with the nucleophile forms Pd(0). The whole process consumes Pd(ll), and ends as a stoichiometric process, because the in situ reoxidation of Pd(0) is hardly attainable. These stoichiometric reactions are treated in this section. 

Reaction Patterns and Various Allylic Compounds Used for Catalytic Reactions... 

In addition to the catalytic allylation of carbon nucleophiles, several other catalytic transformations of allylic compounds are known as illustrated. Sometimes these reactions are competitive with each other, and the chemo-selectivity depends on reactants and reaction conditions. 

Mainly allylic esters are used as the substrates for the catalytic reactions. In addition, the allylic compounds shown are known to react with Pd(0) to form TT-allylpalladium complexes. Even allylic nitro compounds[8,9] and sul-fones[KM2] are used for the allylation. The reactivities of these allylic compounds arc very different. 

Furthermore, the catalytic allylation of malonate with optically active (S)-( )-3-acetoxy-l-phenyl-1-butene (4) yields the (S)-( )-malonates 7 and 8 in a ratio of 92 8. Thus overall retention is observed in the catalytic reaction[23]. The intermediate complex 6 is formed by inversion. Then in the catalytic reaction of (5 )-(Z)-3-acetoxy-l-phenyl-l-butene (9) with malonate, the oxidative addition generates the complex 10, which has the sterically disfavored anti form. Then the n-a ir rearrangement (rotation) of the complex 10 moves the Pd from front to the rear side to give the favored syn complex 6, which has the same configuration as that from the (5 )-( )-acetate 4. Finally the (S)-( )-mal-onates 7 and 8 are obtained in a ratio of 90 10. Thus the reaction of (Z)-acetate 9 proceeds by inversion, n-a-ir rearrangement and inversion of configuration accompanied by Z to isomerization[24]. 

In 1980, Katsuki and Sharpless communicated that the epoxidation of a variety of allylic alcohols was achieved in exceptionally high enantioselectivity with a catalyst derived from titanium(IV) isopropoxide and chiral diethyl tartrate. This seminal contribution described an asymmetric catalytic system that not only provided the product epoxide in remarkable enantioselectivity, but showed the immediate generality of the reaction by examining 5 of the 8 possible substitution patterns of allylic alcohols all of which were epoxidized in >90% ee. Shortly thereafter. Sharpless and others began to illustrate the... 

This class of substrate is the only real problematic substrate for the AE reaction. The enantioseleetivity of the AE reaction with this class of substrate is often variable. In addition, rates of the catalytic reactions are often sluggish, thus requiring stoichiometric loadings of Ti/tartrate. Some representative product epoxides from AE reaction of 3Z-substituted allyl alcohols are shown below. 

The landmark report by Winstein et al. (Scheme 3.6) on the powerful accelerating and directing effect of a proximal hydroxyl group would become one of the most critical in the development of the Simmons-Smith cyclopropanation reactions [11]. A clear syw directing effect is observed, implying coordination of the reagent to the alcohol before methylene transfer. This characteristic served as the basis of subsequent developments for stereocontrolled reactions with many classes of chiral allylic cycloalkenols and indirectly for chiral auxiliaries and catalysts. A full understanding of this phenomenon would not only be informative, but it would have practical applications in the rationalization of asymmetric catalytic reactions. 

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