Scheme 2
strate 5e, which would be expected to provide a relatively
Notes and references
stable benzylic cation (see 27), undergoes multiple 1,2-shifts,
resulting in 23. It is likely that in the formation of 19 and 20,
oxaspirohexanes 5a and 5b undergo phenyl migration concur-
rently with ring opening (equivalent to direct conversion of 26
to 29). With 5a the carbonium ion corresponding to 29
appears to be converted to the product in a reasonably effi-
cient fashion. However, this is not the case with 5b. The pres-
ence of other isomers was indicated by GC/MS, although we
were unable to isolate any other clean, clearly identiÐable
products. It seems likely that both directions of initial
rupture operate with 5c and 5d. Although 4-
methylenetetrahydrodrofurans 21 and 22 were the products
present in the largest yield, our observation of 25 in the
rearrangement of 5c conÐrms that initial O4ÈC5 cleavage also
occurred.
The importance of the nature of the substituents in control-
ling reaction outcomes is further illustrated by the tem-
peratures required for the reactions. Those substrates
containing a phenyl at C5 provided products under the
mildest conditions. The compounds lacking substitution at C5
required an elevated temperature for reaction. There was no
improvement in results at an elevated temperature for the
other oxaspirohexanes. Because of the involvement of multiple
steps in going from reactant to product and the availability of
alternative pathways, it is not surprising that the rearrange-
ments of oxaspirohexanes occur with less efficiency and
greater divergence in outcomes than the reorganizations of the
corresponding oxaspiropentanes (see 10 to 12).
1
L. M. Dollinger, A. J. Ndakala, M. Hashemzadeh, G. Wang, Y.
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2
3
4
5
6
7
8
9
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12 All new compounds are fully characterized and the requisite data
can be found in the electronic supplementary information. Com-
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In summary, we have demonstrated that oxaspirohexanes
can be efficiently prepared from the corresponding 2-methyl-
eneoxetanes using the Furukawa modiÐcation of the
SimmonsÈSmith reaction. Preliminary studies of the reactivity
of the oxaspirohexanes have shown that their behavior on
exposure to BF É Et O is governed by the nature of the sub-
20 For recent examples see: (a) S. Gain•-Rahimi, C. Steeneck, I.
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3
2
stituents on the oxetane ring. Further studies are underway to
see if the efficiency of any of these reactions can be improved
by employing alternative Lewis acids or if the outcome can be
more e†ectively controlled.
21 B. M. Trost and M. J. Bogdanowicz, J. Am. Chem. Soc., 1973, 95,
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22 F. Mahuteau-Betzer and L. Ghosez, T etrahedron L ett., 1999, 40,
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Acknowledgement
A. R. H. thanks the NSF for a CAREER award.
23 N. W. A. Geraghty and P. A. Murphy, T etrahedron L ett., 1994,
35, 6737.
New J. Chem., 2001, 25, 673È675
675