Sakurai multicomponent reactions

Pospisil J, Kumamoto T, Marko IE (2006) Highly diastereoselective silyl-modified sakurai multicomponent reaction. Angew Chem Int Ed 45 3357-3360... 

J. PospSil, T. Kumamoto, I. E. Marko, Angew. Chem. Int. Ed. 2006, 45, 3357-3360. Highly diastereoselective silyl-modi-fied Sakurai. Multicomponent reaction. 

The last category is the class of MCRs catalyzed by organometallic species (MC-MCRs). MC-MCRs include the palladium-catalyzed multicomponent reaction of vinyl compounds [52], the three-component Sakurai allylation reaction [53], metal-catalyzed three-component reactions between alkynes, amines, and... 

Recently, a new multicomponent condensation strategy for the stereocontrolled synthesis of polysubstituted tetrahydropyran derivatives was re-published by the Marko group, employing an ene reaction combined with an intramolecular Sakurai cyclization (IMSC) (Scheme 1.14) [14]. The initial step is an Et2AlCl-promoted ene reaction between allylsilane 1-50 and an aldehyde to afford the (Z)-homoallylic alcohol 1-51, with good control of the geometry of the double bond. Subsequent Lewis acid-media ted condensation of 1-51 with another equivalent of an aldehyde provided the polysubstituted exo-methylene tetrahydropyran 1-53 stereoselectively and... 

In this chapter, only the most recent multicomponent versions of the Hosomi-Sakurai reaction will be covered [68b], in particular those that allowed the synthesis of homoallylic ethers through the combination of an aldehyde (or ketone) with a silyl ether or the corresponding alcohol and an allylsilane (Scheme 12.13, Eq. 1). And also, the synthesis of homoallylic amines where the allylsilane reacts with an imine in situ formed from the carbonyl compound and an amine is known as aza-Sakurai reaetion (Scheme 12.13, Eq. 2). 

SCHEME 12.13 Multicomponent (aza-)Hosomi-Sakurai reactions synthesis of homoallylic ethers (Eq. 1) and synthesis of homoaUylic amines (Eq. 2). 

Finally, Chen s work on the direct allylation of carbonyl compounds using benzyl alcohol in the multicomponent Sakurai reaction catalyzed by selective and green solid acids, such as sihcomolybdic acid (SMA-SiO ) [92] or perchloric acid (HClO -SiOj) [93], both supported on silica gel, should be mentioned. In some cases, the use of preformed acetals as substrates provided better results. These methods allowed the synthesis of a broad number of homoallylic ethers in moderate to high yields in a short reaction time. Significantly, catalyst loading of HClO -SiOj is only 2mol%. 

HomoallyUc amines are useful intermediates in the synthesis of biologically active compounds such as statin, conine, lobeline, sedamine, SKF-1(K)330-A, epothilone, p-lactams, p-amino acids, and many natural products. The synthesis of those interesting precursors is also possible starting from an imine instead of a carbonyl compound, through this kind of reactivity, known in this case as aza-Sakurai reaction [94, 95]. Its multicomponent version involves the in situ formation of that imine, and few recent examples are shown here. 

Another elegant example of a multicomponent aza-Sakurai reaction was reported by Jarvo in 2009 [99]. In this case, Pd(OAc)j was used as catalyst both for the generation in situ of the aUylsilane from allyl trifluoroacetate and HMDS and also for the allylation of the in situ formed imine fi om the corresponding aldehydes and anisidine (H NPMP) (Scheme 12.22). This was concluded after a study base on competition experiments. This procedure allows the synthesis of a variety of homoallylic amines in good to excellent yields (67-96%), starting from different substrates including electron-rich aromatic and aliphatic aldehydes. 

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