Soderquist reagents for allyl-, allenyl-, and propargylboration

The Soderquist group at the University of Puerto Rico recently reported a number of versatile synthetic methods employing pseudoephedrine (PE)-derived borabicyclodecane auxiliaries 676675 and 676683 for the preparation of chiral secondary alcohols.^1-3 Readily prepared by resolution of 676667 with PE, these auxiliaries are air-stable, crystalline solids (Scheme 1).

Treatment of the chiral borabicyclodecanes with the appropriate Grignard reagent cleanly provides allyl-, allenyl-, or propargylboration reagents for preparation of homoallylic and homopropargylic alcohols, or α-allenyl carbinols from aldehydes (Scheme 2). The reactions are rapid (~3 h) and high-yielding, and superb selectivities are observed. Moreover the degree of asymmetric induction is only minimally affected by temperature and is independent of the presence of Mg salts. This is in sharp contrast to the standard Brown allylation protocol employing allyldiisopinocampheylborane (Ipc₂Ballyl) where salt-free conditions and low temperatures (–100 °C) are required. Precursor 676667 can be used directly with Grignard reagents if racemic alcohols are desired.

Importantly, the chiral borabicyclodecanes can be recovered in high yield by simply working up the reaction mixture with the appropriate PE enantiomer followed by filtration and recrystallization. Alternatively, standard oxidative work-up conditions can be employed if there is no need to recycle the boron scaffold.

This methodology provides a straightforward method to prepare a multitude of functionalized non-racemic secondary alcohols from a single reagent. As shown in Figure 1, a diverse set of synthons can be prepared in high yield. In all instances, the borabicyclodecane reagent 676675 was recovered in ~70% yield or greater.

Finally, these reagents perform well in asymmetric crotylborations,¹ allylborations of imines,⁴ and alkynylborations of N-acylimines.⁵ The synthesis of isomerically pure allenylborane reagents from alkynylboranes derived from 676675 or 676683 has also been reported.⁶

Sigma-Aldrich is pleased to add these new tools to our growing arsenal of C–C bond forming reagents.

Product Information

Product #	Product Name/Description	Structure	Add to Cart
676667	B-Methoxy-10-trimethylsilyl-9-borabicyclo[3.3.2]decane, 95%
676675	9-(1S,2S-Pseudoephedrinyl)-(10R)-(trimethylsilyl)-9-borabicyclo[3.3.2]decane
676683	9-(1R,2R-Pseudoephedrinyl)-(10S)-(trimethylsilyl)-9-borabicyclo[3.3.2]decane

• Aldrichimica Acta review on pinane-based allylboranes (Click here to view.)

References:
(1) Burgos, C. H. et al. J. Am. Chem. Soc. 2005, 127, 8044.
(2) Lai, C.; Soderquist, J. A. Org. Lett. 2005, 7, 799.
(3) Hernandez, E.; Soderquist, J. A. Org. Lett. 2005, 7, 5397.
(4) Hernandez, E. et al. Pure Appl. Chem. 2006, 7, 1389.
(5) Gonzales, A. Z. et al. Org. Lett. 2006, 8, 3331.
(6) Canales, E. et al. Angew. Chem., Int. Ed. 2007, 46, 397.