Aldehydes Roush allylboronation

A number of applications in the synthesis of complex structures have been documented. The versatility of the Roush allylboron reagents is demonstrated in the diverse range of substrates that have been successfully employed. In a formal total synthesis of ikarugamycin, the diene in 31 was protected as the iron complex, and the aldehyde in 31 underwent crotylation to afford 33 in 98% ee (Equation 5) [63]. 

Roush reported another tartrate boronate, (E )-y-[(menthofuryI)-dimethyl silyl]-allylboronate 130, for untz -a-hydroxyallyation of aldehydes. Reagent 130 can be obtained from commercially available menthofuran, which was selected... 

Roush et al. discovered that the tartrate ester-modified allylboronates, such as diisopropyl tartrate allylboronate (.S, .S )-41, react with achiral aldehydes to give the homoallylic alcohols 42 in good yields and high levels of enantioselectivity of up to 87% ee when the reaction is carried out in toluene in the presence of 4-A molecular sieves20 (Scheme 3.1q). To rationalize the asymmetric induction realized by 41, two six-membered transition states were compared (Scheme 3.1r). It was reasoned that transition state A was favored over transition state B due mainly to the nonbonded electronic repulsive interactions of the lone-pair electrons of the aldehyde oxygen and the carbonyl oxygen of the tartrate ester. 

Roush, W R, Adam, M A, Walts, A E, Harris, D J, Stereochemistry of the reactions of substituted allylboronates with chiral aldehydes. Factors influencing aldehyde diastereofacial selectivity, J. Am. Chem. Soc., 108, 3422-3434, 1986. 

Roush asymmetric allylation Reaction of allylboronates with aldehydes to give homoallylic alcohols. 386... 

Roush, W. R., Walts, A. E., Hoong, L. K. Diastereo- and enantioselective aldehyde addition reactions of 2-allyl-1,3,2-dioxaborolane-4,5-dicarboxylic esters, a useful class of tartrate ester modified allylboronates. J. Am. Chem. Soc. 1985,107, 8186-8190. 

Roush, W. R., Grover, P. T. Diisopropyl tartrate (E)-Y-(dimethylphenylsilyl)allylboronate, a chiral allylic alcohol 3-carbanion equivalent for the enantioselective synthesis of 2-butene-1,4-diols from aldehydes. Tetrahedron Lett. 1990, 31,7567-7570. 

The synthesis and use of tartrate-modified allylboronate 1 was first reported by Roush and co-workers in 1985. The synthesis and use of the corresponding (E)- and (. -crotylboronate reagents 2 and 3 was published by Roush and co-workers shortly thereafter. The ease of synthesis, stability and efficient reactivity of these reagents offers advantages over many other allyl- and crotylmetal reagents. Roush and co-workers have extensively explored the enantioselective allylations with achiral aldehydes as well as the... 

The allylboronate reagent 1 was used twice in the synthesis of (-)-lasubine I by Wang and Liao. (-)-Lasubine I (67) is a bioactive alkaloid isolated from the Lythraceae plant.(-)-Lasubine I contains three stereocenters in a quinolizidine core. Roush allylation of aldehyde 63 with provided the 1,3-aminoalcohol 67 in > 90 < 10 diastereoselectivity. Alcohol protection and alkene oxidation provided an intermediate aldehyde which underwent Roush allylation with to provide homoallylic... 

Roush has crafted a class of allyl/vinyl diboron reagents that participate in sequential aldehyde addition 1,5-anti-diols reactions and enable the expeditious synthesis of 1,5-diols. The hydroboration reaction of allene 34 furnishes 35, treatment of which with aldehydes results in the formation of 36 (Scheme 5.6) [64]. These allylboronate adducts subsequently undergo addition to a second set of aldehydes, generating 1,5-anti-diols 37 with high diastereoselectivity (S 20 1) and optical purity (S 89% ee). Use of the bulkier boronate 38 gives 1,5-syn-diols 39 with equally high stereoselectivity (dr >14 1, ee>91%) [65]. 

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