Stereoselective synthesis allyl organometallics

Metallic tin, Sn(0), is even more effectively employed. For example, in the presence of Sn(0), allyl bromide and a-halocarbonyl compounds afford nucleophilic organometallic species, which add to aldehydes in good yields to give homoallylic alcohols (12) and g-hydroxycarbonyl compounds (13,14) respectively. a-Diketones could be reduced by activated Sn(0), to give tin(II) enediolates which in turn undergo aldol reaction to form a,g-dihydroxyketones (15,16). This reaction was successfully applied to a stereoselective synthesis of methyl D-glucosaminate (17). 

D. Hoppe, W. R. Roush, E. J. Thomas, Formation of C-C Bonds by Addition to Carbonyl Groups (C—O)—Allyl-Type Organometallic Compounds, in Methoden Org. Chem. (Houben-Weyl) 4th ed. 1952, Stereoselective Synthesis (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann, Eds.), Vol. E21b, 1357, Georg Thieme Verlag, Stuttgart, 1995. 

We have seen in Section 1.1.3 that reactions of many allyl organometallics and chiral C=X electrophiles proceed with only modest levels of relative diastereoselection. Significant improvement in dia-stereoselectivity is possible, however, by using double asymmetric synthesis, that is, by using the highly enantioselective allyl metal reagents described in Section 1.1.4 rather than the less diastereoface-selec-tive achiral allyl metal compounds discussed in Section 1.1.3. Double asymmetric synthesis is also... 

Hoppe D (1995) Formation of C-C bonds by addition of aUyl-type organometallic compounds to carbonyl compounds. Allyl alkali metal reagents (M=Li, Na, K). In Helmchen G, Hoffmann RW, Mulzer J, Schaumann E (eds) Houben-Weyl, Stereoselective synthesis, vol. E 21b, 4th edn. Thieme-Verlag, Stuttgart, p 1379... 

Studies on the stereochemical outcome of the reaction of 2-alkenyl organometallic reagents with aldehydes have increased recently, largely because stereoselectively produced homoallylic alcohols are synthetically equivalent, by cleavage at the carbon-carbon double bond, to the type of aldol adduct stereoisomers required for macrolide antibiotic total synthesis. A new stereoselective synthesis of (Z)-2-alkenyltins (46a) or the corresponding silanes (46b) from allyl or vinyl 9-BBN derivatives has appeared (Scheme 20). The... 

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