C O M M U N I C A T I O N S
Table 1. Synthesis of Bispropionates from Synthons 3 and 4
for Felkin model “mismatched” cases with aldehyde 12 (i.e., from
(S,R)-3 and (S,S)-4). To validate the structural assignment for
product 15, we prepared (-)-invictolide 2117 by Pd-C-catalyzed
hydrogenation of 15 (Scheme 3).17b
In summary, the new bispropionate synthons 3 and 4 are easily
prepared in stereochemically pure form and undergo stereospecific
transfer to a variety of aldehydes to provide rapid access to highly
functionalized polypropionate products. Current research activities
include the application of this synthetic methodology to more
complex natural product structures.
Acknowledgment. This research was supported by the National
Institutes of Health (CA-59703).
Supporting Information Available: Procedures and characteriza-
tion data for all new compounds. This material is available free of
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a Procedure A: TMSOTf (10 mol %), CH2Cl2, -78 °C, 4 h, pyridine
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Procedure B: same as procedure A, except followed by Ac2O, pyridine.
Scheme 3. A Short Synthesis of Invictolide
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(16) The corresponding silyl ether-protected analogues of 12 underwent
desilylation in the course of attempted allylic rearrangement, thus the
acetate protective group was preferred with this substrate.
This methodology was then evaluated with (R)-2-methylpentanal
(11)14 and (2R,3S)-3-acetoxy-2,4-dimethylpentanal (12)15 (Table 1).
In these cases, catalytic TMSOTf was used in the first step
(procedure A) to minimize epimerization of the chiral aldehydes.
From aldehyde 12, the initial products from 3 were observed to
undergo partial migration of the acetate protective group,16 thus
acetylation of the product mixture was employed to produce 17
and 18 (procedure B). The bispropionate transfer reaction occurs
without observable double diastereoselection from R-chiral aldehyde
11, but some diminution in yield and stereoselectivity is observed
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1983, 24, 1893. (b) Honda, T.; Yamane, S.-i.; Ishikawa, F.; Katoh, M.
Tetrahedron 1996, 52, 12177 and cited ref 4 within.
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