A facile synthesis of 5-acyl-6-alkyl/aryl-2,2-dimethyl-1,3-dioxin-4-ones

Full text of DOI:10.1021/jo000730p

8
096
J . Org. Chem. 2000, 65, 8096-8099
tion at C
6
are known (2, R ) OBn, OEt, etc., R′ ) H).10
A F a cile Syn th esis of 5-Acyl-6-a lk yl/
a r yl-2,2-d im eth yl-1,3-d ioxin -4-on es
These are prepared via alcoholysis of formyl Meldrum’s
acid (4, R ) H) followed by acetonide formation from the
resultant formyl malonic half acid (5, R ) OBn, OEt, etc.,
R′ ) H). This is not a general method for the synthesis
R. Daniel Little* and Wade A. Russu
Department of Chemistry and Biochemistry, University of
California, Santa Barbara, California 93106
of derivatives of 2 where there is substitution at C
6
and
an ester functional group at C due to decarboxylation
5
little@chem.ucsb.edu
Received May 13, 2000
during the alcoholysis of the acyl Meldrum’s acids (e.g.,
4, R ) alkyl, aryl), which results in the formation of
â-keto esters.11
In tr od u ction
The masked â-keto acid, 2,2,6-trimethyl-1,3-dioxin-4-
one (1), has shown considerable versatility in organic
synthesis. For instance, 1 has been shown to participate
1
2
in [2 + 2] cycloadditions, act as a Michael acceptor, and
undergo selective alkylation at the γ-carbon of the enone
unit. Additionally, 1 is a source of acylketene which can
3
be intercepted by alcohols and amines to give â-keto
4
esters or amides, respectively. The acylketene interme-
diate, generated upon thermolysis of 1, has also been
shown to undergo cycloaddition reactions with dieno-
philes to give various heterocyclic compounds.5 Such
synthetic versatility warrants investigations aimed at the
development of general methodology for the synthesis of
,9b
Resu lts a n d Discu ssion
We report a facile and general two-step synthesis of
-substituted-5-acyl-2,2-dimethyl-1,3-dioxin-4-ones (2).
1
,3-dioxin-4-ones of novel or rare substitution patterns.
6
In general 1,3-dioxin-4-ones are synthesized by acetonide
We envisioned a synthetic strategy that took advantage
of the existing methods for the formation of the hetero-
6
formation from the enol form of â-keto acids or by cyclo-
addition of a ketone with an acylketene usually derived
6
7
8
cyclic core, starting from â-keto acids. This strategy calls
thermally from a furanone or acyl-Meldrum’s acid.
for the synthesis of both acyl acetoacetic acids and acyl
malonic acids. We opted to use the methodology devel-
oped by Rathke and co-workers for the synthesis of such
compounds.12 Thus, for the synthesis of the 6-substituted-
A class of 1,3-dioxin-4-ones that are of particular inter-
est have a carbonyl functional group (either ketone or
carboxylic ester) at C , and an alkyl or aryl group at C ,
5 6
and are represented by structure 2. Such 1,3-dioxin-4-
ones are potential precursors to functionalized hetero-
cycles and interesting s-cis constrained dienes, which
may be of use in the Diels-Alder cycloaddition reaction.
To our knowledge there does not yet exist a general route
to this type of 1,3-dioxin-4-ones. In fact, in the case where
5
-acyl-2,2-dimethyl-1,3-dioxin-4-ones (2) we chose to start
from tert-butyl acetoacetate. The presence of the tert-
butyl ester would allow us to avoid a saponification step
before formation of the heterocyclic core. tert-Butyl aceto-
acetate was acylated with various acid chlorides in di-
chloromethane in the presence of pyridine and magne-
sium chloride according to the procedure of Rathke and
co-workers.12 After workup, the acyl tert-butyl acetoace-
tates were not characterized and were carried on crude
and subjected directly to the conditions for formation of
the dioxinone, according to the procedure of Kato and co-
5
a ketone moiety is substituted at C of compound 2 only
9
one example exists (R ) R′ ) t-Bu). This compound is
prepared via a cycloaddition reaction of a ketone with
the unusually stable ketene, dipivaloylketene (3). This
method is not general, however, due to the instability of
diacylketenes under the conditions used for their genera-
6
tion. In the case where 2 is substituted at C
5
with an
workers. Under these conditions, as expected, both regio-
ester functional group, only esters possessing no substitu-
isomeric dioxinone products 8a -f and 9b-e are formed.
*
To whom correspondence should be addressed.
1) (a) Baldwin, S. W.; Wilkinson, J . M.J . Am. Chem. Soc. 1980, 102,
634-3635. (b) Winkler, J . D.; Hey, J . P.; Hannon, F. J .; Williard, P.
G. Heterocycles 1987, 25, 55-60.
2) Smith, A. B.; Leuenberg, P. A.; J erris, P. J .; Scarborough, R. M.;
Woukulich, P. M. J . Am. Chem. Soc. 1981, 103, 1501-1508.
3) Smith, A. B.; Scarborough, R. M. Tetrahedron Lett. 1978, 44,
193-4196.
4) Clemens, R. J .; Witzeman, J . S. J . Am. Chem. Soc. 1989, 111,
186-2193.
5) (a) Sato, M.; Yoneda, N.; Kaneko, C. Chem. Pharm. Bull. 1986,
4, 621-627. (b) Sakaki, J .; Sugita, Y.; Sato, M.; Kaneko, C. Tetrahe-
(
3
(
(
4
2
3
(
(
dron 1991, 47, 6197-6214.
6) Kato, T.; Sato, M.; Ogasawara, H.; Oi, K. Chem. Pharm. Bull.
983, 31, 1896-1901.
7) Andreichikov, Y. S.; Gein, L. F.; Plakhina, G. D. Zhu. Org. Khim.
980, 16, 2336-2339.
8) Sato, M.; Sekiguchi, K.; Ogasawara, H.; Kaneko, C. Synthesis
985, 224-225.
9) (a) Wentrup, C.; Kennard, C. H. L.; Evans, R. A.; Kappe, C. O.
(
1
1
1
(
(10) Sato, M.; Kaneko, C.; Katgiri, N.; Takayama, K.; Hirose, M.
Chem. Pharm. Bull. 1989, 37, 665-669.
(
(11) (a) Oikawa, Y.; Sugano, K.; Yonemitsu, O. J . Org. Chem. 1978,
43, 2087-2088. (b) Sorensen, U. S.; Falch, E.; Krogsgaard-Larsen, P.
J . Org. Chem. 2000, 65, 1003-1007.
(
J . Am. Chem. Soc. 1991, 113, 4234-4237. (b) Wentrup, C.; Kollenz,
G.; Kappe, C. O. Monatsh. Chem. 1993, 124, 1133-1141.
(12) Rathke, M. W.; Cowan, P. J . J . Org. Chem. 1985, 50, 2622-
2624.
1
0.1021/jo000730p CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/26/2000

Notes
Ta ble 1. Th e Syn th esis of 8 a n d 9 fr om ter t-Bu tyl
J . Org. Chem., Vol. 65, No. 23, 2000 8097
Acetoa ceta te
products
(ratio)
yield
(%)
a
b
entry
acid halide
CH3COCl
EtCOCl
PhCH2COCl
PhCOCl
R
1
2
3
4
5
6
CH3
Et
8a (na)c
70
67
62
65
67
60
8b, 9b (85:15)
8c, 9c (80:20)
8d , 9d (75:25)
8e, 9e (90:10)
PhCH2
Ph
2-IC6H4
2-IC6H4COCl
4-NO2C6H4COCl 4-NO2C6H4 8f
a
1
Ratios were determined by integration of the H NMR spectra
utility in heterocyclic synthesis. Thermolysis of 8a in the
presence of phenylisocyanate gave 15 in 65% (unopti-
mized) yield.13 Additionally, the ketone functionality
b
of the crude reaction mixtures. Yields are of the combined,
isolated isomers. na ) not applicable.
c
All substrates were smoothly converted to the dioxinone
product.
Table 1 reveals this method to be a general route to
6
-alkyl/aryl-5-acyl-2,2-dimethyl-1,3-dioxin-4-ones 8 and
9
and gives satisfactory yields for the two-step procedure.
Note also that iodo and nitro aromatic substituents
entries 5 and 6) are compatible with the conditions,
which allows for possible further elaboration of the
products.
may be selectively reduced in the presence of the ester
using Luche conditions.14 Attempted mesylation of the
alcohol 16 gave the diene 17, presumably via an in situ
elimination of the desired mesylate under the reaction
conditions.
(
It is interesting to note that in all cases examined the
major product is the methyl ketone, 8. This preference
may possibly be explained by imagining a mechanism
wherein a magnesium enolate 10 is the reactive inter-
mediate. The acid chloride can be attacked by this species
to form a new magnesium chelate 11a , in which the
oxygen that came from the acid chloride is now associated
with the magnesium. Deprotonation at the R carbon of
rotomer 11b allows elimination of chloride ion forming
the enol after workup. Dioxinone formation from this enol
form results in the formation of the major product, while
a keto-enol tautomerization under the conditions for
dioxinone formation can give rise to the minor product.
In the case where 4-nitrobenzoyl chloride was used as
the acylating agent, the methyl ketone 8f was the only
observed product. We feel that the electron-withdrawing
nature of the nitro functional group may stabilize enol
form 7f enough to render it the preferred reactive species.
We believe that the type of dioxinones that are now
accessible through the methodology presented above will
prove to be valuable synthetic intermediates. We are
actively investigating the chemistry of these compounds
and will report our findings in due course.
Exp er im en ta l Section
Gen er a l. Melting points were obtained using a hot-stage
1
apparatus and are uncorrected. H NMR (200 or 400 MHz) and
1
3
C NMR (25 or 125 MHz) were recorded in chloroform-d.
Dichloromethane was distilled from CaH before use. All other
2
chemicals were obtained from commercial sources and used
without further purification.
Gen er a l P r oced u r e for th e Syn th esis of 6-Su bstitu ted -
The attempted synthesis of the 6-substituted-5-car-
boxyl-1,3-dioxin-4-ones (2, R ) OBn) followed the same
general strategy as that discussed above but called for
the use of a malonate ester. We chose to use benzyl tert-
butyl malonate (12) as the starting material. This
promised to allow us to exploit the differential reactivity
of the ester groups. Thus, the malonate 12 was acylated
in acetonitrile in the presence of triethylamine and
magnesium chloride according to the procedure of Rathke
and co-workers.1 Again, the crude products 13 were to
be taken on to the dioxinone product without purification
or characterization. However, in this case it was found
that the â-keto ester 14 was the only observed product.
5-k eto-1,3-d ioxin -4-on es. Dry MgCl
added to 5 mL of CH Cl and stirred. Neat tert-butyl acetoacetate
0.79 g, 5.0 mmol) was then added, and the mixture was cooled
2
(0.47 g, 5.0 mmol) was
2
2
(
via an ice/water bath. Pyridine (0.80 mL, 10.0 mmol) was added,
and the cold mixture was stirred for 15 min. Neat acid chloride
(5 mmol) was then added dropwise. The cold reaction mixture
was allowed to stir for 15 min. The reaction mixture was then
warmed to room temperature and stirred for 1 h. The reaction
was quenched with ice-water and extracted with EtOAc. The
combined organic layers were washed with saturated brine and
dried over sodium sulfate. Filtration with subsequent concentra-
tion in vacuo resulted in an oil that was then dissolved in acetone
(0.58 mL) and acetic anhydride (1.3 mL) and then cooled to -20
2
(13) J a¨ ger, G.; Wenzelburger, J . Liebigs Ann. Chem. 1976, 1689-
712.
1
A preliminary investigation into the chemistry of these
new dioxinones demonstrates their potential synthetic
(
14) Luche, J .-L.; Gemal, A. L.J . Am. Chem. Soc. 1981, 103, 5454-
5459.

8
098 J . Org. Chem., Vol. 65, No. 23, 2000
Notes
°
C. To the reaction mixture was added dropwise concentrated
(Nujol, NaCl) 1734, 1666, 1585, 1462, 1376 cm-1; HRMS (CI,
sulfuric acid (0.25 mL). After 5 min at -20 °C, the cooling bath
4 14 4
CH ) calcd for C14H O I (M + H) 372.9936, found 372.9942.
5-Ace t yl-6-(4-n it r op h e n yl)-2,2-d im e t h yl[1,3]d ioxin -4-
was exchanged for an ice-water bath and stirring continued for
1
2
h. The reaction mixture was stored in a refrigerator (5 °C) for
0 h. The reaction was then quenched with ice-cold 10% aq
on e (8f). Pale yellow needles (hexanes-ethyl acetate) mp 92-
1
94 °C. H NMR (CDCl ) δ 8.28 (d, 2H, J ) 9.0), 7.61 (d, 2H, J )
3
sodium carbonate solution under ice cooling and stirred for 30
min. The mixture was then extracted with EtOAc. The combined
organic layers were washed with saturated brine and dried over
sodium sulfate. After filtration and concentration in vacuo, the
9.0), 2.60 (s, 3H), 1.87 (s, 6H); 13C NMR δ 196.6, 168.3, 159.2,
149.7, 137.9, 130.3, 123.8, 111.2, 107.6, 32.2, 25.3; FTIR (Nujol,
NaCl) 2922, 2854, 1740, 1679, 1539, 1524, 1461, 1375 cm-1
;
HRMS (FAB, m-nitrobenzyl alcohol) calcd for C14H14NO (M +
6
crude oil was chromatographed on silica (CH
hexanes) to give the pure product.
2
Cl
2
or 30% Et
2
O/
H) 292.0821, found 292.0814.
Attem p ted Syn th esis of 2,2,6-Tr im eth yl-5-ben zyloxy-
Six acylating agents were used. The following data lists each,
the product(s), number(s), and yield. Acetyl chloride, 8c (colorless
oil), 0.64 g (3.5 mmol), 70%; propionyl chloride, 85/15 mixture
of 8b/9b, 0.66 g (3.3 mmol), 67%; phenylacetyl chloride, 80/20
mixture of 8c/9c, 0.80 g (3.1 mmol), 62%; benzoyl chloride, 75/
ca r bon yl[1,3]d ioxin -4-on e (2, R ) OBn, R′ ) Me). Dry MgCl
2
(
0.47 g, 5.0 mmol) was added to 5 mL CH CN and stirred. Neat
3
benzyl tert-butyl malonate (1.25 g, 5.0 mmol) was then added,
and the mixture was cooled via an ice/water bath. Triethylamine
(1.39 mL, 10.0 mmol) was added, and the cold mixture was
2
5 mixture of 8d /9d , 0.79 g (3.2 mmol), 65%; 2-iodobenzoyl
chloride, 90/10 mixture of 8e/9e, 1.24 g (3.3 mmol), 67%;
-nitrobenzoyl chloride, 8f, 0.87 g (3.0 mmol), 60%.
-Acetyl-2,2,6-tr im eth yl[1,3]d ioxin -4-on e (8a ). 1H NMR
CDCl
) δ 2.54 (s, 3H), 2.33 (s, 3H), 1.71 (s, 6H); 13C NMR (CDCl
δ 197.2, 177.3, 159.7, 108.8, 106.2, 32.3, 25.3, 21.0; FTIR (neat,
stirred for 15 min. Neat acetyl chloride (0.39 g, 5.0 mmol) was
then added dropwise. The cold reaction was allowed to stir for
4
1
5 min. The reaction mixture was then warmed to room
5
temperature and stirred for 1 h. The reaction was quenched with
ice-water and extracted with EtOAc. The combined organic
layers were washed with saturated brine and dried over sodium
sulfate. Filtration with subsequent concentration in vacuo
resulted in an oil that was then dissolved in acetone (0.58 mL)
and acetic anhydride (1.3 mL) and then cooled to -20 °C. To
the reaction mixture was added dropwise concentrated sulfuric
acid (0.25 mL). After 5 min at -20 °C, the cooling bath was
exchanged for an ice-water bath and stirring continued for 1
h. The reaction mixture was stored in a refrigerator (5 °C) for
(
3
3
)
-
1
NaCl) 2921, 1735, 1685, 1560, 1388, 1350 cm ; HRMS (CI, NH
calcd for C 185.0813 (M + H), found 185.0810.
-Acetyl-6-eth yl-2,2-d im eth yl[1,3]d ioxin -4-on e (8b). Col-
3
)
9
13 4
H O
5
1
orless oil. H NMR (CDCl
3
) δ 2.64 (q, 2H, J ) 7.6 Hz), 2.54 (s,
1
3
3
1
H), 1.71 (s, 6H), 1.18 (t, 3H, J ) 7.6 Hz); C NMR (CDCl
3
) δ
97.2, 180.7, 159.9, 108.5, 106.1, 32.3, 26.9, 25.3, 11.1; FTIR
(
1
neat, NaCl) 2990, 1732, 1682, 1563, 1381, 1359, 1269, 1206,
064 cm ; HRMS (CI, CH ) calcd for C10H O 199.0970 (M +
4 15 4
-
1
2
0 h. The reaction was then quenched with ice cold 10% aq
H), found 199.0974.
,2,6-Tr im eth yl-5-p r op ion yl[1,3]d ioxin -4-on e (9b). Color-
less oil. H NMR (CDCl
3
2
sodium carbonate solution under ice cooling and stirred for 30
min. The mixture was then extracted with EtOAc. The combined
organic layers were washed with saturated brine and dried over
sodium sulfate. After filtration and concentration in vacuo the
2
1
3
) δ 2.95 (q, 2H, J ) 7.2 Hz), 2.29 (s,
1
3
H), 1.70 (s, 6H), 1.08 (t, 3H, J ) 7.2 Hz); C NMR (CDCl
3
) δ
00.4, 176.4, 159.3, 108.7, 106.1, 37.1, 25.3, 20.7, 8.3; FTIR (neat,
crude oil was chromatographed on silica (CH
hexanes) to give 0.49 g (3.1 mmol, 62%) of benzyl acetoacetate
14) as a colorless oil: 1H NMR (CDCl
) δ 7.34 (m, 5H), 5.27 (s,
H), 3.48 (s, 2H), 2.22 (s, 3H).
-Acetyl-6-m eth yl-3-p h en yl-1,3-oxa zin e-2,4-d ion e (15). To
2 2 2
Cl or 30% Et O/
-
1
NaCl) 2977, 1728, 1687, 1391, 1378, 1343, 1249, 951 cm
;
15
HRMS (CI, CH
99.0975.
-Acetyl-6-ben zyl-2,2-d im eth yl[1,3]d ioxin -4-on e (8c). Col-
4 15 4
) calcd for C10H O 199.0970 (M + H), found
(
3
1
2
5
5
1
orless oil. H NMR (CDCl
3
) δ 7.33 (m, 5H), 3.96 (s, 2H), 2.57 (s,
H), 1.58 (s, 6H); C NMR (CDCl ) δ 197.1, 176.0, 163.6, 134.8,
29.5, 128.8, 127.4, 109.3, 106.4, 38.2, 32.3, 25.1; FTIR (neat,
a solution of 8a (0.37 g, 2.0 mmol) in toluene was added phenyl
isocyanate (0.59 g, 5.0 mmol), and the solution was refluxed (125
1
3
3
1
3
°C, oil bath temp.) for 20 h. The solution was then concentrated;
-1
NaCl) 3000, 1732, 1685, 1560, 1365 cm ; HRMS (CI, CH
for C15 (M + H) 261.11268, found 261.11198.
,2,6-Tr im eth yl-5-ph en ylacetyl[1,3]dioxin -4-on e (9c). Col-
4
) calcd
chromatography on silica gel (hexanes-ether) gave 0.31 g (1.3
17 4
H O
mmol, 65% yield) of a colorless plates (EtOAc): mp 172-174
2
1
°
C; H NMR (CDCl
3
) δ 7.53 (m, 3H), 7.28 (m, 2H), 2.58 (s, 3H),
1
orless oil. H NMR (CDCl
3
) δ 7.25 (m,5H), 4.26 (s, 2H), 2.21 (s,
H), 1.56 (s, 6H); C NMR (CDCl ) δ 197.3, 176.4, 159.7, 135.0,
29.9, 128.8, 127.0, 108.4, 106.4, 50.3, 25.1, 20.4; IR (neat, NaCl)
004, 2938, 1730, 1689, 1584, 1390, 1352 cm-1; HRMS (CI, CH
(M + H) 261.11268, found 261.11305.
-Acetyl-2,2-dim eth yl-6-ph en yl[1,3]dioxin -4-on e (8d). Col-
13
2
1
2
3
.49 (s, 3H); C NMR (CDCl ) δ 196.6, 170.5, 170.4, 147.0, 133.3,
29.9, 129.8, 128.0, 114.9, 32.1, 19.2; FTIR (Nujol, NaCl) 2923,
853, 1775, 1697, 1685, 1627, 1457, 1400, 1376 cm ; HRMS
1
3
3
1
3
3
-1
4
)
(
CI, CH
-(1-Hyd r oxyeth yl)-2,2,6-tr im eth yl[1,3]d ioxin -4-on e (16).
To a solution of 8a (0.55 g, 3.0 mmol) in MeOH (6 mL) and CeCl
O (1.1 g, 3.0 mmol) was added NaBH (0.11 g, 3.0 mmol) in
4 4
) calcd for C13H12NO (M + H) 246.0766, found 246.0776.
calcd for C15
17 4
H O
5
5
3
‚
1
3
orless needles (hexanes-ether) mp 57-58 °C. H NMR (CDCl )
7
H
2
4
1
3
δ 7.44 (m, 5H), 2.52 (s, 3H), 1.83 (s, 6H); C NMR (CDCl
3
) δ
97.5, 169.6, 159.7, 132.5, 131.6, 129.2, 128.7, 109.9, 106.6, 32.2,
5.2; FTIR (Nujol, NaCl) 2923, 2853, 1728, 1676, 1558, 1458,
one portion. An exothermic reaction took place with vigorous
evolution of gas. The solution was allowed to stir for 5 min after
which time the solution was made neutral by the addition of
1
2
1
2
-
1
366 cm ; HRMS (CI, CH
46.0897.
4 14 4
) calcd for C14H O 246.0892, found
0
.1 N HCl. Extraction of the solution with EtOAc followed by
drying of the organic layer with Na SO with susequent filtration
2
4
2
,2,6-Tr im eth yl-5-ben zoyl[1,3]d ioxin -4-on e (9d ). White
and concentration gave a residue which was chromatographed
1
waxy solid. H NMR (CDCl
m, 2H), 2.14 (s, 3H), 1.83 (s, 6H); C NMR (CDCl
71.8, 158.4, 137.9, 133.6, 129.4, 128.7, 108.2, 106.9, 25.6, 19.2;
FTIR (neat, NaCl) 2987, 1727, 1666, 1602, 1450, 1265 cm
3
) δ 7.84 (m,2H), 7.58 (m, 1H), 7.47
on silica (hexanes-ether) to give 0.43 g of 16 as a colorless oil
1
3
(
1
3
) δ 195.9,
1
(
2.3 mmol, 78% yield). H NMR (CDCl
3
) δ 4.56 (q, 1H, J ) 6.6
Hz), 3.38 (s broad, 1H), 2.01 (s, 3H), 1.65 (s, 3H), 1.63 (s, 3H),
-
1
.
1
1
2
.45 (d, 3H, J ) 6.6 Hz); 13C NMR (CDCl
3
) δ 163.6, 162.1, 108.3,
5
-Ace t yl-2,2-d im e t h yl-6-(2-iod op h e n yl)[1,3]d ioxin -4-
05.5, 65.0, 25.3, 24.8, 23.5, 17.2; IR (neat, NaCl) 3449, 2974,
930, 1717, 1636, 1392, 1270, 1206.
1
on e (8e). White plates (hexanes-ether) mp 85-86 °C. H NMR
CDCl ) δ 7.86 (dd, 1H, J ) 7.6, 0.8), 7.41 (td, 1H, J ) 7.6, 0.8),
.21 (dd, 1H, J ) 7.6, 1.6), 7.14 (td, 1H, J ) 7.6, 1.6), 2.49 (s,
H), 1.87 (s, 6H); C NMR (CDCl
38.0, 131.6, 129.4, 128.2, 110.2, 107.7, 94.5, 31.7, 25.6; FTIR
(
3
2
,2,3-Tr im eth yl-5-vin yl[1,3]d ioxin -4-on e (17). To 4 mL of
Cl were added 0.37 g of 16 (2.0 mmol) and 0.55 mL (4.0
7
3
1
1
3
CH
2
2
3
) δ 195.0, 173.1, 159.5, 139.5,
mmol) of triethylamine, and the solution was cooled in an ice/
water bath. To the cooled solution was added dropwise 0.55 mL
(2.0 mmol) of methanesulfonyl chloride. After the addition was
complete the solution was allowed to warm to room temperature
and stir for 2 h. The reaction was poured into water and
extracted with EtOAc. The combined organics were washed with
(
1
3
Nujol, NaCl) 2923, 2853, 1727, 1672, 1622, 1560, 1537, 1455,
-
1
376 cm ; HRMS (CI, CH
72.9936, found 372.9944.
4 14 4
) calcd for C14H O I (M + H)
2
,2,6-Tr im eth yl-5-(2-iod oben zoyl)[1,3]d ioxin -4-on e (9e).
1
Pale yellow needles (hexanes-ether) mp 98-99 °C. H NMR
CDCl ) δ 7.84 (dd, 1H, J ) 8.0, 1.2), 7.39 (td, 1H, J ) 7.6, 1.2),
.31 (dd, 1H, J ) 7.6, 2.0), 7.11 (td, 1H, J ) 8.0, 2.0), 2.41 (s,
H), 1.78 (s, 6H); C NMR (CDCl
39.6, 131.4, 128.7, 128.1, 107.7, 106.9, 91.3, 25.9, 20.7; FTIR
2 4
a saturated brine solution and dried over Na SO and subse-
(
3
7
3
1
1
3
3
) δ 194.0, 178.1, 158.4, 145.7,
(15) Baker B. R.; Schaub, R. E.; Querry, M. V.; Williams, J . H. J .
Org. Chem. 1952, 17, 77-96.

Notes
J . Org. Chem., Vol. 65, No. 23, 2000 8099
quently filtered and concentrated. Chromatography of the
Foundation (NSF), and Dr. J ames Pavlovich for obtain-
ing high resolution mass spectra.
resultant residue on silica (hexanes-ether) gave 0.28 g of 17
1
(
1.7 mmol, 84% yield). H NMR (CDCl
3
) δ 6.33 (dd, 1H, J ) 17.6,
1
1
1
1.6 Hz), 5.76 (dd, 1H, J ) 17.6, 1.6 Hz), 5.50 (dd, 1H, J ) 11.6,
.6 Hz), 2.10 (s, 3H), 1.66 (s, 6H); 13C NMR (CDCl
) δ 165.2,
60.5, 126.9, 117.8, 105.18, 105.15, 25.3, 18.1; HRMS (EI) calcd
168.0786, found 168.0779.
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
3
spectra of all new compounds (8a -f, 9b-e, 15, 16, 17) and
C APT spectra of representative compounds (8a , 8b, 8e, 8f,
b, 9e, 16, 17) are available free of charge via the Internet at
1
3
9 12 3
for C H O
9
http://pubs.acs.org.
Ack n ow led gm en t. The authors gratefully acknowl-
edge the financial support of the National Science
J O000730P