Carbonyl asymmetric allylation

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

The chemistry of asymmetric allylation of carbonyl compounds has further progressed since the review in Comprehensive Asymmetric Catalysis [1] and plenty of papers including reviews [2,3] on chiral catalysts for the reaction have since appeared. This chapter describes new examples of catalytic enantioselec-tive allylation of carbonyl compounds with allylmetals in the presence of a catalytic amount of chiral Lewis acid or chiral Lewis base (Scheme 1). Compounds 1-36 [4-49] shown in Fig. 1 are the chiral catalysts reported since 1998, which have been used in the asymmetric allylation or propargylation of carbonyl compounds. Chiral compounds 37-40 [50-53], which have been utilized in the stoichiometric version, are also candidates for the chiral catalyst (Fig. 2). 

The effectiveness of various substituted BINOL ligands 12-16 in the Zr(IV)-or Ti(IV)-catalyzed enantioselective addition of allyltributyltin to aldehydes was also investigated by Spada and Umani-Ronchi [21], The number of noteworthy examples of asymmetric allylation of carbonyl compounds utilizing optically active catalysts of late transition metal complexes has increased since 1999. Chiral bis(oxazolinyl)phenyl rhodium(III) complex 17, developed by Mo-toyama and Nishiyama, is an air-stable and water-tolerant asymmetric Lewis acid catalyst [23,24]. Condensation of allylic stannanes with aldehydes under the influence of this catalyst results in formation of nonracemic allylated adducts with up to 80% ee (Scheme 3). In the case of the 2-butenyl addition reac-... 

Catalytic asymmetric allylation of aldehydes and ketones with allylsilanes can be achieved by using chiral Lewis acids, transition metal complexes, and Lewis bases. In recent years, much attention has been paid for the chiral Lewis base-catalyzed system using allyltrichlorosilanes. Advances in catalytic asymmetric carbonyl allylation have been described in detail in recent reviews.116,117,117a... 

Asymmetric Coiyugate Addition of Allyl- and Crotylphosphonamides/ The asymmetric C-allylation of a, 3-unsaturated carbonyl compounds is a powerful tool for the functionalization of a carbonyl compound in the P-position. Since such a process normally leads to the corresponding enolate derivative when anionic reagents are used, there exists the possibility of trapping with an electrophile. Thus sequential addition and trapping can lead to vicinally substituted carbonyl compounds. Asymmetric allylation has been achieved previously with simple cycloalkenones using phosphorus and sulfur based reagents that must be prepared in diastereomerically pure form. 

Asymmetric allylation of carbonyl substrates and their derivatives is currently of particular interest in the synthesis of a wide range of optically active compounds, owing to the easy derivatization of the carbon-carbon double bond to a desired functional group. The strategy for reaching this goal can be classified into three approaches ... 

Chiral-auxiliary modified aldehydes. A well-established strategy for the asymmetric allylation of aldehydes is the conversion of the aldehyde carbonyl group to an acetal with a chiral diol [41]. Despite the excellent selectivities achieved, this... 

By a similar method, the (Z)-crotylborate is synthesized from cA-2-butene in 70-75% yield with a 98% isomeric purity. The tartrate esters of allylboronic acids are an excellent reagent for asymmetric allylboration of carbonyl compounds. Allyl(diisopinocampheyl)borane [51] and the allylic boron derivatives of ester and amide, such as camphordiol [52], pinanediol [53], 1,2-diphenyl-1,2-ethylenediamine [54], have also been successfully used for asymmetric allylboration of carbonyls. 

Asymmetric allyation of carbonyl compounds to prepare optically active secondary homoallyhc alcohols is a useful synthetic method since the products are easily transformed into optically active 3-hydroxy carbonyl compounds and various other chiral compounds (Scheme 1). Numerous successful means of the reaction using a stoichiometric amount of chiral Lewis acids or chiral allylmetal reagents have been developed and applied to organic synthesis however, there are few methods available for a catalytic process. Several reviews of asymmetric allylation have been pubHshed [ 1,2,3,4,5] and the most recent [5] describes the work up to 1995. This chapter is focussed on enantioselective allylation of carbonyl compounds with allylmetals under the influence of a catalytic amount of chiral Lewis acids or chiral Lewis bases. Compounds 1 to 19 [6,7,8,9,10,11,12,... 

Chiral titanium complexes 4 and 5, which were developed as chiral catalysts for asymmetric carbonyl-ene reactions with prochiral glyoxylate esters [50], were first apphed to the catalytic asymmetric allylation of carbonyl compounds by Mikami and Nakai (Scheme 5) [9]. The titanium catalysts are prepared from (S)-binaphthol and diisopropoxytitanium dihahde (X=C1 and Br) in the presence of 4 A molecular sieves. Using these catalysts, glyoxylates are enantio- and diastereoselectively allylated with allylic trimethylsilanes or allylic tributylstan-nanes. High levels of enantioselectivity and syn selectivity are observed for (E)-crotylsilane and -stannane. The syn selective allylation reaction is believed to proceed mainly through an antiperiplanar transition state. 

Addition reactions. Asymmetric allyl transfer from allyl boronates to A-acyl imines is assisted by (5)-3,3 -diphenyl-BINOL Alkenyldimethoxyboranes react with conjugated carbonyl compounds with excellent enantioselectivity in the presence of a chiral 3,3 -diiodo-BINOL. ... 

Both carenes 40 and 41 are readily hydroborated by borane dimethyl sulfide complex to give the diisocaranylboranes (Icr.BH) which can be isolated in pure form. Treatment w ith methanol gives the S-methoxy derivatives, which readily react with allylic carbanions to give the corresponding allyldiisocaranylboranes 42-45. These compounds have been used for asymmetric allyl additions to carbonyl compounds (Sections D. 1.3.3.3. and D.2.5.2.). The reagents 44 and 45, derived from 2-carene39, are more enantioselective than those from 3-carene(1. 

Nishida, M., Tozawa, T., Yamada, K. and Mukaiyama, T. (1996) Asymmetric allylation of aromatic aldehydes using chiral allylic tin reagents. Chemistry Letters, 25,1125-1126 Yamada, K., Tozawa, K., Nishida, M. and Mukaiyama, T. (1997) Asymmetric allylation of carbonyl compounds with tartrate-modified chiral allylic tin reagents. Bulletin of the Chemical Society of Japan, 70, 2301-2308. 

Several types of Zr-catalyzed asymmetric allylation of carbonyl compounds with allylstannanes were reported [38] as shown below. In all cases, Zr-BINOL complexes were used as a catalyst along with additives such as phenolic ketone (74) (Equations 33 and 34), [39] pivalonitrile (Equation 35), [40] and MeOH (Equation 36) [41]. 

Catalytic enantioselective protonation of prochiral ketone enolates is a beneficial route to optically active carbonyl compounds possessing a tertiary asymmetric carbon at the a-position. In the asymmetric protonation of trimethylsilyl enolates with methanol, BINAP-AgF has been found to act as a chiral catalyst [90,91], which is also known to catalyze asymmetric allylation of aldehydes with allylic trimethoxysilanes [42] as well as asymmetric aldol reaction with trimethoxysilyl enolates [54]. This protonation can be most effectively performed using 6 mol% ofBINAP and 10 mol% of... 

Allylation of carbonyl compounds is another very useful carbon-carbon bond forming asymmetric transformation in organic synthesis. This transformation yields the homoallylic alcohols that have proven to be valuable reagents and intermediates that have found numerous applications in natural product total synthesis. In particular, asymmetric allyl-boration of aldehydes employing tartrate- and pinane-derived reagents has been widely exploited. Although the asymmetric allylation reaction is well documented and widely used in solution phase, the asymmetric variant of the allylation of carbonyl compounds on the solid support has remained largely unexplored. ... 

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