Tert-Butyl Hypofluorite - An Electrophilic tert-Butoxylation Agent

Article abstract of DOI:10.1021/jo9723366

tert-Butyl hypofluorite, t-BuOF, easily synthesized from Z-BuOH and F₂, is a unique source of the novel electrophilic tert-butoxylium moiety t-BuO⁺. It was added to several benzylic double bonds to form vicinal fluoro-tert-butoxide derivatives. Not surprisingly, this bulky reagent is quite sensitive to steric hindrance. The process is electrophilic in nature, but since the reaction is relatively slow (20-60 min) formation of various radical species can take place, forming eventually several distinct byproducts. t-BuOF was also reacted with a number of enols, producing the corresponding α-tert-butoxy ketone derivatives in moderate to good yields. The best results were obtained with benzylic enol derivatives.

Full text of DOI:10.1021/jo9723366

4632
J . Org. Chem. 1998, 63, 4632-4635
ter t-Bu tyl Hyp oflu or itesAn Electr op h ilic ter t-Bu toxyla tion Agen t
Iris Ben-David, Eyal Mishani, and Shlomo Rozen*
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences,
Tel-Aviv University, Tel-Aviv 69978, Israel
Received December 31, 1997
tert-Butyl hypofluorite, t-BuOF, easily synthesized from t-BuOH and F2, is a unique source of the
novel electrophilic tert-butoxylium moiety t-BuO+. It was added to several benzylic double bonds
to form vicinal fluoro-tert-butoxide derivatives. Not surprisingly, this bulky reagent is quite sensitive
to steric hindrance. The process is electrophilic in nature, but since the reaction is relatively slow
(20-60 min) formation of various radical species can take place, forming eventually several distinct
byproducts. t-BuOF was also reacted with a number of enols, producing the corresponding R-tert-
butoxy ketone derivatives in moderate to good yields. The best results were obtained with benzylic
enol derivatives.
While the chemistry of the negatively charged tert-
a mixture of 1 and 5 was reacted with less than 1 mol
equiv of t-BuOF, twice as much 6 was obtained compared
to 3, in accordance to the electrophilic nature of the
reagent (Scheme 1). The mainly anti addition mode could
be easily discerned from the reaction with indene (7),
which formed 1R-fluoro-2â-tert-butoxyindan (8) in good
yield. This stereochemistry is in sharp contrast to the
syn addition of all reactions involving electrophilic fluo-
rine.7 The difference is attributed to the geometry of the
electrophile, where, unlike with the small fluorine atom,
the oxygen is capable of forming an oxonium bridge such
as in 8a .
The lower electron density of nonbenzylic double bonds
was responsible for generally more sluggish reactions.
Thus when cyclohexene was reacted with t-BuOF,
only a low yield of a stereoisomeric mixture of 2-fluoro-
tert-butoxycyclohexanes (9) was obtained. This result
prompted us to examine the reactions of t-BuOF with
more electron rich double bonds such as various enol
derivatives.
R-t-Butoxy ketones are known and usually prepared
with the aid of metal catalysts.8 The electrophilic tert-
butoxylium moiety in t-BuOF, by attacking the electron
rich pole of the π regions of various enols, should offer a
novel way to introduce the tert-butoxy group into the
R-position of ketones without the use of heavy metal
agents.
When the enol acetate or the trimethylsilyl enol ether
of 1-indanone (10a or 10b) was treated with t-BuOF,
2-tert-butoxy-1-indanone (11) was isolated in 45% and
40% yield, respectively. Similarly, tetralone trimethyl-
silyl enol ether 12b or its methyl enol ether 12c afforded
the expected 2-tert-butoxy-1-tetralone (13) in good yields.
The reaction seems to proceed through an addition
elimination pathway, associated with most electrophilic
reagents possessing the OF moiety.9 Support for this
assumption could be found in the reaction of tert-butyl
butoxide is well-established, the chemistry of the tert-
butoxylium species is practically nonexistent. A few
years ago we developed the HOF‚CH3CN complex,1 in
which the fluorine-bound hydroxylium moietysHO+s
reacts as an electrophile and is used for powerful oxida-
tions, fast epoxidations, and various hydroxylation reac-
tions.2 More recently, we have demonstrated that the
elusive CH3OF, the smallest unknown organic molecule
at the time, could be synthesized and serve as a source
of the methoxylium species, MeO+, used in electrophilic
methoxylations.3 t-BuOF was the second member4 of the
alkyl hypofluorite family to be prepared, isolated, and
fully characterized.5 As with CH3OF, the fluorine-bound
tert-butoxylium moiety, t-BuO+,6 seems to possess an
electrophilic nature, a feature which is demonstrated
here in its reactions with various π centers.
tert-Butyl hypofluorite can be easily prepared by the
reaction of fluorine with tert-butyl alcohol using aceto-
nitrile as a solvent. Its isolation and purification are
quite tedious, but these steps are usually unnecessary,
since it can be used in situ as generated. t-BuOF adds
smoothly across unhindered benzylic double bonds such
as in styrene (1) or 1-vinylnaphthalene (2), forming
1-fluoro-1-phenyl-2-tert-butoxyethane (4) or 1-fluoro-1-
naphthyl-2-tert-butoxyethane (3) in 60% yield each. The
regiochemistry of the reaction (we have not detected any
1-aryl-1-tert-butoxyethane derivatives) strongly suggests
an initial electrophilic attack of the tert-butoxylium
moiety. A somewhat better yield was obtained with the
more electron rich double bond of 4-methoxystyrene (5),
which gave the corresponding adduct 1-fluoro-1-(4-meth-
oxyphenyl)-2-tert-butoxyethane (6) in 70% yield. When
(1) Rozen, S.; Brand, M. Angew. Chem., Int. Ed. Engl. 1986, 25, 554.
(2) Rozen, S. Acc. Chem. Res. 1996, 29, 243.
(3) Rozen, S.; Mishani, E.; Kol, M.; Ben-David, I. J . Org. Chem. 1994,
59, 4281. Kol, M.; Rozen, S. J . Org. Chem. 1993, 58, 1593. Rozen, S.;
Mishani, E.; Kol, M. J . Am. Chem. Soc. 1992, 114, 7643.
(4) The third member of this family, CX3CD2OF (X ) H, D), was
also prepared but proved to be very unstable: Rozen, S.; Bar-Haim,
A. J . Fluorine Chem. 1995, 74, 229.
(7) Rozen, S.; Lerman, O. J . Org. Chem. 1980, 45, 4122. Rozen, S.;
Lerman, O.; Kol, M.; Hebel, D. J . Org. Chem. 1985, 50, 4753. Rozen,
S.; Brand, M. J . Org. Chem. 1986, 51, 3607. Rozen, S.; Bareket, Y.;
Kol, M. J . Fluorine Chem. 1993, 61, 141.
(8) a) Takebayashi, M.; Ibata, T.; Kohara, H.; Kim, B. H. Bull. Chem.
Soc. J pn. 1967, 40, 2392. (b) Nakatsuka, T.; Mukaiyama, T. Chem.
Lett. 1982, 369.
(5) Appelman, E. H.; French, D.; Mishani, E.; Rozen, S. J . Am. Chem.
Soc. 1993, 115, 1379.
(6) It should be noted that as with F+ and CH3O+, the notation
t-BuO+ only indicates that in the transition state the tert-butoxylium
pole acts as an electrophile with the counterpole being a good leaving
group. For more detailed discussion, see: Lerman, O.; Tor, Y.; Hebel,
D.; Rozen, S. J . Org. Chem. 1984, 49, 806.
(9) Rozen, S. Chem. Rev. 1996, 96, 1717.
S0022-3263(97)02336-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/18/1998

t-BuOF as an Electrophilic tert-Butoxylation Agent
J . Org. Chem., Vol. 63, No. 14, 1998 4633
Sch em e 1
Sch em e 3
It should be noted that in all reactions of 10 and 12
small amounts of 2-fluoro-1-indanone (16)10 and 2-fluoro-
1-tetralone (17)11 were formed, as well as 2-dichloro-
methylene-1-indanone (18) in the case of 10. Small
amounts of 1-naphthol (19) or 1-naphthyl methyl ether
(20), from the reaction of 12b and 12c respectively, were
also detected. We believe that the formation of these
byproducts is the outcome of the relatively long reaction
times needed for the bulky (CH3)3COF to react, inevitably
resulting in some radical decomposition of the reagent,
whose half-life time at room temperature is about 1 h.
In addition to forming small amounts of fluorine radicals,
this decomposition also induced the formation of CCl3
radicals from the chloroform used as a solvent. This
competitive radical decomposition was also evident when
the electron-poor double bond of 1-hexene was the
substrate. With usual reaction conditions, only tars were
eventually produced, so we substituted the acetonitrile
with propionitrile and added the substrate to the t-BuOF
solution which was cooled to -78 °C. Warming the re-
action mixture slowly did not produce any desired ad-
duct, but we were able to isolate 2,3-dicyanobutane,12
which apparently resulted from coupling of two R-pro-
pionitrile radicals, CH3CH•CN.
Sch em e 2
Enol derivatives of open chain benzylic ketones also
proved to be suitable substrates. Acetophenone tri-
methylsilyl enol ether (21b) gave 2-tert-butoxy-acetophe-
none (22)8a in 50% yield, while the less sterically hindered
methyl enol ether 21c was converted into 22 in a higher
yield of 65% (Scheme 3). Similarly, o-methoxyacetophe-
none methyl enol ether (23c) gave 2-tert-butoxy-o-meth-
oxyacetophenone (24) in 50% yield. In both cases, minor
byproducts identified as 3-cyanopropiophenone (25)13 and
3-cyano-o-methoxypropiophenone (26)14 (15% yield each)
were also obtained from solvent (CH3CN) incorporation,
apparently through a radical pathway. We have also
hypofluorite with 10a , in which an intermediate A was
isolated and characterized (Scheme 2). This adduct,
however, was unstable and eventually decomposed to the
expected 11. Another question was whether the incor-
porated tert-butoxy group originated from the reagent or
from some secondary reaction with tert-butyl alcohol,
present in the reaction medium. We treated 3,4-dihy-
dropyrane (14), an enol ether of an aldehyde, with tert-
butyl hypofluorite in the presence of methanol as a
competitive nucleophile. The only isolated product,
3-tert-butoxy-2-methoxytetrahydropyrane (15), is in sup-
port of the electrophilic attack of the tert-butoxylium
moiety. Moreover, addition of nitrobenzene or other
radical scavengers does not change the reaction rate or
the final result.
(10) Neeman, M.; Osawa, Y. J . Am. Chem. Soc. 1963, 85, 232.
(11) Rozen, S.; Menahem, Y. J . Fluorine Chem. 1980, 16, 19.
(12) Whiteley, R. V. J r.; Marianelli, R. S. Synthesis 1978, 392.
(13) Knott, E. B. J . Chem. Soc. 1947, 1190.
(14) Nate, H.; Sekine, Y.; Oda, K.; Aoe, K.; Nakai, H.; Wada, H.;
Takeda, M.; Yabana, H.; Nagao, T. Chem. Pharm. Bull. 1987, 35,
3253.

4634 J . Org. Chem., Vol. 63, No. 14, 1998
Ben-David et al.
acid or trimethylsilyl triflate/triethylamine). The methyl enol
ethers were prepared by mixing 1 mol equiv of the appropriate
ketone with 1.1 mol equiv of trimethyl orthoformate, in the
presence of 0.005 mol equiv of p-toluenesulfonic acid at room
temperature overnight. The methanol and methyl formate
formed were distilled off slowly for at least 4 h until no more
methanol was formed. The methyl enol ethers were distilled
under reduced pressure. Most of the enol derivatives are
known, so spectral data are only reported for the few unknown
compounds.
reacted the more sterically hindered propiophenone tri-
methylsilyl enol ether (27) with t-BuOF, resulting in
2-tert-butoxypropiophenone (28) in moderate yield. Here
too, it was possible to detect a small amount of 2-fluoro-
propiophenone (29)15 as a byproduct. 5-Acetylindan tri-
methylsilyl enol ether (30) was also reacted to give 5-tert-
butoxyacetylindan (31), along with small amounts of 5-(1-
cyano-3-propanone)indan (32) and 5-(1,1-dichloro-1-en-
3-propanone)indan (33).
tert-Butoxylation with tert-butyl hypofluorite seems to
be of limited use with aliphatic and nonbenzylic ketones.
The methyl enol ethers of 4-tert-butyl cyclohexanone and
adamantyl methyl ketone, as well as trimethylsilyl enol
ethers of pinacolone and cyclooctanone, did not react
satisfactorily and produced either tars or very low yields
of the desired R-tert-butoxy ketones. This probably
reflects the relatively low electron density of the enolic
double bond of aliphatic ketones, resulting in insufficient
nucleophilicity toward t-BuOF.
Rea ction of t-Bu OF w ith styr en e (1) was carried out as
described to give 1-fluoro-1-phenyl-2-tert-butoxyethane (3) as
an oil, in 60% yield.5
Rea ction of t-Bu OF w ith 1-vin yln a p h th a len e (2) gave
1-fluoro-1-naphthyl-2-tert-butoxyethane (4): oil, 60% yield; 1H
NMR 7.85-7.43 (7 H, m), 5.73 (1 H, ddd, J 1 ) 48 Hz, J 2 ) 8
Hz, J 3 ) 3 Hz), 3.89-3.5 (2 H, m), 1.18 (9 H, s); 19F NMR
-183.98 (m); 13C NMR 132.9-123.4, 93.9 (d, 1J CF ) 174.5 Hz),
2
73.6 (s), 66.13 (d, J CF ) 25 Hz), 27.4 (s); MS m/z 246 (M+),
173 (M - t-BuO)+. Anal. Calcd for C16H19FO: C, 78.04; H,
7.72; F, 7.72. Found: C, 77.56; H, 7.86; F, 7.72.
R ea ct ion of t-Bu OF w it h 4-m et h oxyst yr en e (5) gave
1-fluoro-1-(4-methoxyphenyl)-2-tert-butoxyethane (6): oil, 60%
1
yield; H NMR 7.35-7.25 (2 H, m), 6.96-6.84 (2 H, m), 5.48
Exp er im en ta l Section
(1 H, ddd, J 1 ) 48 Hz, J 2 ) 8 Hz, J 3 ) 3 Hz), 3.8 (3 H, s),
1H NMR and decoupled 13C NMR spectra were recorded with
200 and 360 spectrometers, with CDCl3 as solvent and Me4Si
as internal standard. The 19F NMR spectra were measured
at 338.8 MHz and are reported in ppm upfield from CFCl3,
which also served as internal standard. IR spectra were
recorded as neat films, in CHCl3 solution or in KBr pellets.
Gen er a l P r oced u r e for Wor k in g w ith F lu or in e. Fluo-
rine is a strong oxidant and a very corrosive material. An
appropriate vacuum line made from copper or monel in a well-
ventilated area should be constructed for working with this
element. Additional experimental information on how we
handle it may be found in ref 16. For the occasional user,
however, various premixed mixtures of F2 in inert gases are
commercially available, simplifying the whole process. The
reactions themselves can be carried out in glass vessels. If
elementary precautions are taken, work with fluorine is
relatively simple, and we have had no bad experiences working
with it.
3.6-3.45 (2 H, m), 1.21 (9 H, s); 19F NMR -131.23 (m); 13C
1
NMR 127.4-113.6, 93.4 (d, J CF ) 182 Hz), 73.5 (s), 65.96 (d,
2J CF ) 25 Hz), 55.2, 27.4; MS m/z 206 (M - HF)+.
Rea ction of t-Bu OF w ith in d en e (7) was carried out as
described, forming 1R-fluoro-2â-tert-butoxyindan (8): oil, 70%
1
yield; H NMR 7.65-7.24 (4 H, m), 5.8 (1 H, dd, J 1 ) 57 Hz,
J 2 ) 4.8 Hz), 4.6-4.4 (1 H, m), 3.29 (1 H, dd, J 1 ) 16 Hz, J 2
) 8 Hz), 2.82 (1 H, ddd, J 1 ) 16 Hz, J 2 ) 6.6 Hz, J 3 ) 4 Hz),
1.18 (9 H, s); 19F NMR -177.4 (dd, J 1 ) 57 Hz, J 2 ) 22.3 Hz);
2
13C NMR 129.4-124.8, 101.4 (d, 1J CF ) 180.6 Hz), 78.5 (d J CF
3
) 21 Hz), 74.25, 38.48 (d, J CF ) 5 Hz), 28.3 (s); MS m/z 208
(M+), 151 (M - t-Bu)+, 135 (M - t-BuO)+. Anal. Calcd for
C
13H17FO: C, 75.0; H, 8.17; F, 9.13. Found: C, 74.65; H, 7.75;
F, 9.09.
Rea ction of t-Bu OF w ith cycloh exen e was carried out
as described, forming cis- and trans-2-fluoro-tert-butoxycyclo-
hexane (9) as an oil, in 20% yield. The cis isomer: 1H NMR
4.59 (1 H, dm, J 1 ) 50 Hz, Wh/ 2 ) 10 Hz), 3.5-3.39 (1 H, m),
2.1-1.2 (8 H, m), 1.18 (9 H, s); 19F NMR -178.9 (m); 13C NMR
P r ep a r a tion a n d Gen er a l Rea ction s of t-Bu OF .
A
1
2
mixture of 15% F2 in N2 was bubbled for 1 h at a rate of 200
mL/min into a cold (-40 °C) solution of 7.5 mL (CH3)3COH in
173 mL of CH3CN placed in a Teflon vessel. The amount of
the (CH3)3COF thus obtained could easily be determined by
reacting aliquots of the reaction mixture with aqueous KI and
titrating the liberated iodine. After the desired concentration
of t-BuOF was achieved, usually around 0.1-0.2 M, a cold (0
°C) solution of the substrate in CHCl3 was added and the
mixture allowed to warm to 0 °C. The reactions were usually
carried out on scales of 3-20 mmol using a 5-10-fold excess
of t-BuOF. It should be noted that although pure liquid
t-BuOF can explode,5 it is perfectly safe when diluted with
solvents. The progress of the reactions was usually monitored
by following the disappearance of the oxidizing power of the
reagent (iodometric titration) and starting material (GC). The
duration of the reaction was usually 15-60 min, considerably
slower than other reactions where electrophilic fluorine or
oxygen species, such as HOF‚CH3CN2 or CH3OF,3 are involved.
The term “usual work up” refers to terminating the reaction
by pouring it into NaHCO3 solution, extracting with CHCl3,
washing the organic layer with water until neutral, drying it
over MgSO4, and finally evaporating the solvent. The crude
reaction mixture was usually subjected to vacuum flash
chromatography using Silica gel 60-H (Merck) and mixtures
of ethyl acetate in petroleum ether as eluent.
92.46 (d, J CF ) 173.5 Hz), 73.7, 70 (d, J CF ) 17 Hz), 30.6 (d,
2J CF ) 18 Hz), 29.7, 28.4, 23.1, 20.2; MS m/z 174 (M+), 159 (M
- Me)+, 100 (M - t-BuOH)+. The trans isomer: 1H NMR 4.2
(1 H, dm, J 1 ) 47 Hz, Wh/ 2 ) 26 Hz), 3.6-3.5 (1 H, m), 2.1-1.2
(8 H, m), 1.18 (9 H, s).
Rea ction of t-Bu OF w ith 1-in d a n on e en ol a ceta te (10a )
formed a mixture of three compounds, which were chromato-
graphically separated. The least polar fraction proved to be
2-dichloromethylene-1-indanone (18): mp 122 °C; 15% yield;
IR 1702 cm-1; 1H NMR 7.83 (1 H, d, J ) 8 Hz), 7.62 (1 H, t, J
) 8 Hz), 7.5-7.35 (2 H, m), 3.87 (2 H, s); 13C NMR 188, 146,
139, 135, 133.5, 130, 128, 126, 124.7, 35; MS m/z 212 (M+),
177 (M - Cl)+, 149, 114. The second fraction proved to be
2-tert-butoxy-1-indanone (11): mp 70 °C (pentane); 45% yield;
1
IR 1730 cm-1; H NMR 7.74 (1 H, d, J ) 5 Hz), 7.59 (1 H, dt,
J 1 ) 9 Hz, J 2 ) 1 Hz), 7.4-7.2 (2 H, m), 4.38 (1 H, dd, J 1 ) 8
Hz, J 2 ) 5 Hz), 3.45 (1 H, dd, J 1 ) 17 Hz, J 2 ) 8 Hz), 2.99 (1
H, dd, J 1 ) 17 Hz, J 2 ) 5 Hz), 1.34 (9 H, s); 13C NMR 204.9,
150.6, 135.2, 134.7, 127.6, 126.5, 124, 75.0, 74, 36.5, 28.3; MS
m/z 148 (M - t-Bu + H)+, 147 (M - t-Bu)+, 119, 91, 57. Anal.
Calcd for C13H16O2: C, 76.44; H, 7.90. Found: C, 75.95; H,
7.85. The most polar fraction proved to be 2-fluoro-1-indanone
1
(16):10 mp 56 °C; 13% yield; IR 1731 cm-1; H NMR 7.8 (1 H,
d, J ) 8 Hz), 7.68 (1 H, dt, J 1 ) 8 Hz, J 2 ) 1 Hz), 7.5-7.4 (2
H, m), 5.28 (1 H, ddd, J 1 ) 51 Hz, J 2 ) 8 Hz, J 3 ) 5 Hz), 3.64
(1 H, dt, J 1 ) 17 Hz, J 2 ) 8 Hz), 3.24 (1 H, ddd, J 1 ) 23 Hz,
J 2 ) 17 Hz, J 3 ) 5 Hz); 19F NMR -194.5 (ddd, J 1 ) 51 Hz, J 2
) 23 Hz, J 3 ) 7 Hz); MS m/z 150 (M+), 122 (M - CO)+, 102
(M - CO - HF)+. The adduct A was isolated in 6% yield: 1H
NMR 7.6 (1 H, d, J ) 7 Hz), 7.4-7.2 (3 H, m), 4.53 (1 H, ddd,
J 1 ) 15 Hz, J 2 ) 6 Hz, J 3 ) 7 Hz), 3.18 (1 H, dd, J 1 ) 16 Hz,
Syn th esis of En ol Der iva tives. The enol acetates and
silyl enol ethers were prepared from the corresponding ketones
by standard procedures (e.g., with isopropenyl acetate/sulfuric
(15) Elkik, E.; Assadi-Far, H. Bull. Soc. Chim. Fr. 1970, 991.
(16) Hebel, D.; Rozen, S. J . Org. Chem. 1991, 56, 6298.

t-BuOF as an Electrophilic tert-Butoxylation Agent
J . Org. Chem., Vol. 63, No. 14, 1998 4635
J 2 ) 7 Hz), 3.0 (1 H, ddd, J 1 ) 16 Hz, J 2 ) 6 Hz, J 3 ) 4 Hz),
2.11 (3 H, s), 1.28 (9 H, s); 19F NMR -101 (dd, J 1 ) 15 Hz, J 2
) 4 Hz).
Th e r ea ction w ith 10b gave, after the usual workup and
chromatographic separation, three compounds: the least polar
fraction proved to be 18 (10% yield), the second was identified
as 11 (40% yield), and the most polar one proved to be 16 (30%
yield).
workup, two compounds which were chromatographically
separated. The less polar fraction proved to be 2-tert-butoxy-
o-methoxyacetophenone (24): oil, 55% yield; IR 1690 cm-1; 1H
NMR 7.81 (1 H, dd, J 1 ) 8 Hz, J 2 ) 2 Hz), 7.46 (1 H, dt, J 1 )
8 Hz, J 2 ) 2 Hz), 6.99 (2 H, m), 4.64 (2 H, s), 3.91 (3 H, s),
1.27 (9 H, s); 13C NMR 198.6, 158.6, 133.7, 130.4, 125.9, 120.7,
111.3, 73.8, 69.5, 55.4, 27.4; MS m/z 223 (M + H)+, 167, 135
(M - CH2CO-t-Bu)+, 57 (t-Bu)+. Anal. Calcd for C13H18O3: C,
70.24; H, 8.16. Found: C, 69.70; H, 7.95. The more polar
fraction proved to be 3-cyano-o-methoxypropiophenone (26):14
Rea ction of t-Bu OF w ith Tetr a lon e Tr im eth ylsilyl
En ol Eth er (12b). After 30 min the reaction was worked up
as usual. Chromatographic separation gave three compounds;
the least polar fraction proved to be 2-tert-butoxy-3,4-dihy-
dronaphthalenone (13): oil, 40% yield; IR 1698 cm-1; 1H NMR
8.01 (1 H, d, J ) 9 Hz), 7.49-7.24 (3 H, m), 4.19 (1 H, t, J )
8 Hz), 3.08 (2 H, t, J ) 6 Hz), 2.21 (2 H, m), 1.28 (9H, s); 13C
NMR 197.6, 143-125.8, 75.0, 73.6, 32.4, 28.0. Anal. Calcd for
1
oil, 19% yield; H NMR 7.84 (1 H, dd, J 1 ) 8 Hz, J 2 ) 2 Hz),
7.6-7.45 (1 H, m), 7.07-6.95 (2 H, m), 3.95 (3 H, s), 3.41 (2
H, t, J ) 7 Hz), 2.73 (2 H, t, J ) 7 Hz).
Rea ction of t-Bu OF w ith P r op iop h en on e Tr im eth yl-
silyl En ol Eth er (27b). After 40 min reaction time and usual
workup, two compounds were chromatographically separated.
The main fraction (25% yield) was 2-tert-butoxypropiophenone
C
14H18O2: C, 77.06; H, 8.25. Found: C, 76.23; H, 7.80. The
next fraction proved to be 2-fluoro-3,4-dihydronaphthalenone
(17):11 oil, 5% yield; IR 1704 cm-1; 1H NMR 8.0-7.2 (4 H, m),
5.15 (1 H, ddd, J 1 ) 48 Hz, J 2 ) 13 Hz, J 3 ) 6 Hz), 3.07-3.14
(2 H, m), 2.27-2.58 (2 H, m). The most polar fraction proved
to be 1-naphthol (19) (10% yield), identical with an authentic
sample. A similar reaction was performed with tetralone
methyl enol ether (12c), giving again three compounds, which
were chromatographically separated. The least polar fraction
proved to be 1-methoxy naphthalene (20) (15% yield), identical
to an authentic sample. The next fraction proved to be 13,
formed in 55% yield. The most polar one was identified as 17
(15% yield).
Rea ction of t-Bu OF w ith 3,4-d ih yd r op yr a n e (14) was
carried out as described in the presence of methanol. The
adduct 3-tert-butoxy-2-methoxytetrahydropyrane (15) was ob-
tained in 30% yield as an oil: 1H NMR 4.28 (1 H, d, J ) 3
Hz), 3.7 (1 H, m), 3.55-3.45 (2 H, m), 3.40 (3 H, s), 1.90-1.84
(2 H, m), 1.54-1.36 (2 H, m), 1.19 (9 H, s); 13C NMR 102.45,
74.6, 66.67, 61.19, 55.24, 28.28, 27.5, 21.5; MS m/z 188 (M+),
115 (M - Ot-Bu)+, 74 (CH3OCHOCH2)+.
1
(28): mp 70 °C; IR 1687 cm-1; H NMR 8.14 (2 H, dd, J 1 ) 8
Hz, J 2 ) 2 Hz), 7.6-7.4 (3 H, m), 4.73 (1 H, q, J ) 7 Hz), 1.44
(3 H, d, J ) 7 Hz), 1.17 (9 H, s); 13C NMR 203, 134.5, 133,
129, 128, 75, 73, 28, 21.3. Anal. Calcd for C13H18O2: C, 75.69;
H, 8.79. Found: C, 75.47; H, 8.93. The minor product,
although not isolated in pure form, was found to be 2-fluoro-
propiophenone (29):15 1H NMR 5.7 (1 H, dq, J 1 ) 49 Hz, J 2
)
7 Hz), 1.66 (3 H, dd, J 1 ) 24 Hz, J 2 ) 7 Hz); 19F NMR 181.8
(dq, J 1 ) 49 Hz, J 2 ) 24 Hz).
5-Acetylin d a n e Tr im eth ylsilyl En ol Eth er (30) is un-
known and was prepared as described above: 1H NMR 7.48
(1 H, s), 7.41 (1 H, d, J ) 8 Hz), 7.18 (1 H, d, J ) 8 Hz), 4.89
(1 H, d, J ) 2 Hz), 4.40 (1 H, d, J ) 2 Hz), 2.91 (4 H, t, J ) 7
Hz), 2.09 (2 H, quintet, J ) 7 Hz), 0.30 (9 H, s). It was then
reacted with t-BuOF as described above. After 40 min reaction
time and usual workup, three compounds were chromato-
graphically separated. The less polar fraction proved to be
5-(1,1-dichloro-1-en-3-propanone)indan (33): oil, 14% yield; IR
1668 cm-1; 1H NMR 7.77 (1 H, s), 7.71 (1 H, d, J ) 8 Hz), 7.31
(1 H, d, J ) 8 Hz), 7.24 (1 H, s), 2.96 (4 H, t, J ) 7 Hz), 2.12
(2 H, quintet, J ) 7 Hz); 13C NMR 186.8, 151.3, 145.2, 135.3,
134.3 127.2, 124.6, 124.4, 33.0, 32.5, 25.3; MS m/z 240 (M+),
212 (M - C2H4)+, 177 (M - C2H4 - Cl)+, 159, 145 (M -
CHdCCl2)+, 117, 115. The second product was identified as
Rea ction of t-Bu OF w ith Acetop h en on e Tr im eth ylsilyl
En ol Eth er (21b). After 40 min reaction time and usual
workup, two compounds were chromatographically separated.
The least polar fraction obtained in 50% yield proved to be
2-tert-butoxy-acetophenone (22):8a mp 120 °C (pentane/
5-tert-butoxyacetylindane (31): oil, 22% yield; IR 1698 cm-1
;
1
CH2Cl2); IR 1706 cm-1; H NMR 8.0 (2 H, d, J ) 8 Hz), 7.6-
1H NMR 7.82 (1 H, s), 7.76 (1 H, d, J ) 8 Hz), 7.29 (1 H, d, J
) 8 Hz), 4.66 (2 H, s), 2.95 (4 H, t, J ) 7 Hz), 2.10 (2 H, quintet,
J ) 7 Hz), 1.28 (9 H, s); 13C NMR 197, 150, 145, 134, 126.4,
124.2, 123.9, 74.4, 66, 33, 32.5, 27.4, 25; HRMS calcd for
7.4 (3 H, m), 4.67 (2 H, s), 1.29 (9 H, s); 13C NMR 196.5, 135,
132.7, 128, 127.5, 74.0, 65.6, 26.8; MS m/z 149 (M - CO -
CH3)+, 122, 105, 77, 57 (t-Bu)+. The more polar fraction proved
to be 3-cyanopropiophenone (25),13 obtained in 15% yield: mp
C
15H20O2 232.1463 (M)+, found 232.1469. Anal. Calcd for
1
71 °C (hexane/ethanol); IR 1683, 2251 cm-1; H NMR 8.0 (2
C15H20O2: C, 77.55; H, 8.68. Found: C, 76.81; H, 8.30. The
most polar fraction proved to be 5-(1-cyano-3-propanone)indan
H, d, J ) 7 Hz), 7.7-7.5 (3 H, m), 3.4 (2 H, t, J ) 7 Hz), 2.8 (2
H, t, J ) 7 Hz); 13C NMR 195, 135, 134, 129, 128, 119, 34, 12;
MS m/z 105 (PhCO)+, 77. Similarly, the reaction of acetophe-
none methyl enol ether (21c) with t-BuOF gave 22 in 65%
yield.
1
(32): oil, 7% yield; IR 2250, 1721 cm-1; H NMR 3.36 (2 H, t,
J ) 8 Hz), 2.96 (4 H, t, J ) 8 Hz), 2.76 (2 H, t, J ) 8 Hz), 2.13
(2 H, quintet, J ) 8 Hz).
o-Meth oxya cetop h en on e m eth yl en ol eth er (23c) is
unknown and was prepared by the general way described
above. 1H NMR 7.46 (1 H, dd, J 1 ) 8 Hz, J 2 ) 2 Hz), 7.33-
7.24 (1 H, m), 6.98-6.90 (2 H, m), 4.62 (1 H, d, J ) 2 Hz), 4.42
(1 H, d, J ) 2 Hz), 3.86 (3 H, s), 3.72 (3 H, s). Its reaction
with t-BuOF gave, after 20 min reaction time and usual
Ack n ow led gm en t. This research was supported by
the USA-Israel Binational Science Foundation (BSF),
J erusalem, Israel.
J O9723366