C O M M U N I C A T I O N S
no erosion of the 1,2-syn relative configuration.13 Upon treatment
with pyridine and thionyl chloride, syn-3 could be converted into
trans-1,2-disubstituted cyclopropanes 10.14
Scheme 1. Hydrostannylation of Homoallyl Alcohols 4 with 1a
In conclusion, we have demonstrated that the Lewis acidic
hydrostannane 1a is valuable for highly stereoselective homolytic
hydrostannylation of allyl and homoallyl alcohols. The formation
of the Sn-O coordinate bond in the â-stannylalkyl radical
intermediate would be the key factor of the present diastereocontrol.
This work provides a novel example of acyclic stereocontrol of
radical reactions.
Acknowledgment. This work was partly supported by Grants-
in-Aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science, and Technology, Government of Japan.
Scheme 2. Origin of Stereochemical Outcomes
Supporting Information Available: Experimental details and
characterization data (1H NMR, 13C NMR, IR, elemental analysis). This
References
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Scheme 3. Synthetic Use of Stannylated Alcohols 3
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radical intermediate. Judging from the importance of a strong Sn-O
coordination in the stereocontrol, the origin of the stereochemical
outcomes can be reasonably explained by chelation models of the
radical intermediates (7 and 8 in Scheme 2).12 In the hydrostan-
nylation of 2, H-abstraction of 7 from 1a occurs from the opposite
side to R1 to avoid its steric hindrance, affording syn-3 predomi-
nantly. The radical 8 arising from 4 has a six-membered chelate
ring, which takes a chairlike form bearing R1 at the equatorial
position. Since equatorial attack of 1a to the radical center is
sterically favored over axial attack, H-abstraction of 8 followed by
butylation provides syn-5 or cis-6.
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To enhance the synthetic utility of the present stereoselective
hydrostannylation, γ-stannylated alcohols syn-3 were utilized for
C-C bond formation (Scheme 3). Transmetalation of the MEM
ether of syn-3a with BuLi and subsequent reaction with benzalde-
hyde gave 1,4-diol monoether 9 as a diastereomeric mixture with
JA052245N
9
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