Scheme 1
Table 1. [4 + 1] Indanone Annulation
methyl ketones.13 As expected, TAS-arylketenes 3a-g are
remarkably robust ketenes, stable at 25 °C and at mildly
elevated temperatures, and amenable to purification using
conventional silica gel chromatography.
The feasibility of the 2-indanone [4 + 1] annulation
strategy was initially examined using phenyl(triisopropylsi-
lyl)ketene (3a). Treatment of 3a with 1.1 equiv of TMS-
diazomethane14 in a mixture of dichloromethane and hexane
at room temperature produced the desired 1,3-bis(silyl)-
indanone in nearly quantitative yield. Purification of this
compound could not be achieved without partial loss of the
trimethylsilyl group, and consequently, the crude product was
converted to the mono(silyl)indanone 4 by brief stirring at
room temperature in the presence of silica gel. In this fashion,
the desired indanone was obtained in 86% yield as a white
solid, mp 81-82 °C. 2-Indanone itself can be accessed
directly by employing phenyl(triethylsilyl)ketene for the
reaction, in which case both the TMS and TES groups can
(5) Bennett, D. M.; Okamoto, I.; Danheiser, R. L. Org. Lett. 1999, 1,
641.
(6) Loebach, J. L.; Bennett, D. M.; Danheiser, R. L. J. Am. Chem. Soc.
1998, 120, 9690.
(7) For related transformations, see: (a) Colomvakos, J. D.; Egle, I.;
Ma, J.; Pole, D. L.; Tidwell, T. T.; Warkentin, J. J. Org. Chem. 1996, 61,
9522. (b) Huang, W.; Tidwell, T. T. Synthesis 2000, 457.
(8) Scattered reports have appeared previously in which indanone
derivatives were observed in the reaction of diazo compounds with
diarylketenes. See: (a) Kende, A. S. Chem. Ind. (London) 1956, 1053. (b)
Yates, P.; Abrams, G. D.; Betts, M. J.; Goldstein, S. Can. J. Chem. 1971,
49, 2850. (c) Frey, J.; Rappoport, Z. J. Am. Chem. Soc. 1995, 117, 1161.
(d) Le´ost, F.; Doutheau, A. Tetrahedron Lett. 1999, 40, 847.
(9) For generation of silylketenes by photo-Wolff rearrangement, see refs
4-6 and: (a) Maas, G.; Bru¨ckmann, R. J. Org. Chem. 1985, 50, 2801. (b)
Bru¨ckmann, R.; Schneider, K.; Maas, G. Tetrahedron 1989, 45, 5517.
(10) Wolff rearrangement of R-silyl-R-diazo ketones can also be effected
by heating in the presence of catalytic rhodium(II) octanoate; see: Marsden,
S. P.; Pang, W.-K. J. Chem. Soc., Chem. Commun. 1999, 1199.
(11) Silylation was achieved by using our modification4 of the method
of Maas.9a,b
(12) (a) Danheiser, R. L.; Miller, R. F.; Brisbois, R. G.; Park, S. Z. J.
Org. Chem. 1990, 55, 1959. (b) Danheiser, R. L.; Miller, R. F.; Brisbois,
R. G. Organic Syntheses; Wiley: New York, 1998; Collect. Vol. IX, p
197.
(13) The methyl ketone required for the synthesis of 1f was prepared
via Stille coupling of 3-(i-Pr)-C6H4OTf with H2CdC(OEt)SnBu3.
(14) (a) Seyferth, D.; Dow, A. W.; Menzel, H.; Flood, T. C. J. Am. Chem.
Soc. 1968, 90, 1080. (b) Shioiri, T.; Aoyama, T.; Mori, S. Organic Syntheses;
Wiley: New York, 1993; Collect. Vol. VIII, pp 612-615.
a Isolated yields of products purified by column chromatography.
b Desilylation (of the Me3Si group) was achieved by stirring the crude
product in CH2Cl2 over silica gel at rt for 1 h. c Cleavage of both the Me3Si
and Et3Si groups from the crude annulation product was accomplished by
exposure to 1 N HCl in THF at rt for 4 h. d Treatment of the annulation
product with 3 equiv of K2CO3 in MeOH at room temperature for 3 min
effected desilylation. e Cleavage of the Me3Si group from the annulation
product occurred during the column chromatography on silica gel. f Exposure
of the annulation product to 1 N HCl in THF (rt, 3.5 h) effected desilylation.
g Overall yield for two steps from 2g (photo-Wolff rearrangement and [4
+ 1] annulation). h In this case, the annulation was carried out in the
presence of 0.5 equiv of i-Pr2EtN.
be conveniently cleaved by exposure of the crude annulation
product to dilute HCl in aqueous THF.
[4 + 1] Annulation with substituted arylketenes proceeds
smoothly in a similar fashion (Table 1), except for the case
of the 4-carbomethoxy derivative (entry 7), for which
successful reaction requires the addition of 0.5 equiv of i-Pr2-
EtN (vide infra). As indicated in the Table, the optimal
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