Zwitterionic aza-Claisen rearrangement: Reaction of carboxylic acid fluorides with N-allyl amines

Article abstract of DOI:10.1055/s-1999-2530

A significant yield enhancement is observed by replacing carboxylic acid chlorides by the corresponding fluorides in the zwitterionic aza-Claisen rearrangement of N-allyl amines. The von Braun type degradation as the major competing reaction involving the

Full text of DOI:10.1055/s-1999-2530

LETTER
25
Zwitterionic Aza-Claisen Rearrangement: Reaction of Carboxylic Acid
Fluorides with N-Allyl Amines
Stephan Laabs, Andreas Scherrmann, Alexander Sudau, Michel Diederich, Camilla Kierig and Udo Nubbemeyer*
Institut f. Organische Chemie, Freie Universität Berlin, Takustr. 3, D-14195 Berlin, Germany
Fax +30 838 5163, E-mail: udonubb@chemie.fu-berlin.de
Received 5 October 1998
presence of a Pd° catalyst.11 The allyl amines 3, 6 and 7
were isolated in 50 to 80 % yield with allyl inversion; only
traces of the retention products were observed.
Abstract: A significant yield enhancement is observed by replacing
carboxylic acid chlorides by the corresponding fluorides in the zwit-
terionic aza-Claisen rearrangement of N-allyl amines. The von
Braun type degradation as the major competing reaction involving
the chlorides is completely suppressed using the fluorides. In regard
to the initial results, the stereochemical advantages of the method
are maintained.
Key words: Zwitterionic aza-Claisen rearrangement, allyl amines,
carboxylic acid fluorides, von Braun degradation, planar chirality
The zwitterionic aza-Claisen rearrangement of various N-
allyl amines with carboxylic acid chlorides has been de-
veloped as a mild and efficient method to form g,d unsat-
urated amides or lactams.1-3 Beyond the well known
complete 1,3-chirality transfer,1 the major advantages of
the reaction were the high simple diastereoselectivity (in-
ternal asymmetric induction)1 including a 1,4-chirality
transfer2 and the remote stereocontrol (external 1,2-asym-
metric induction), which allows the defined generation of
a new C-C bond adjacent to a chiral C-O function.3
The major problems of the process reported were on the
one hand a von Braun type competing reaction involving
a nucleophilic attack of the chloride ion on an intermedi-
ate acylammonium salt.4 The percentage of the resulting
allyl chlorides depended on the substitution pattern of the
allyl amines employed. On the other hand, several reac-
tions suffered from partial fragmentation to give allyl
amine hydrochlorides in presence of the carboxylic acid
chlorides. The inactive ammonium salts required an aque-
ous work up to regenerate the reactive amines. To achieve
a complete conversion in such cases, the crude reaction
mixture had to be subjected to the reaction conditions for
a second cycle.1-3
With the intention to repress the competing von Braun re-
action of the acylammonium salt generated in situ, we de-
cided to employ carboxylic acid fluorides bearing the less
nucleophilic fluoride counter ion in the zwitterionic aza-
Claisen rearrangement. We choosed the allyl amines 3
and 6 to 10 for our investigations, which, by the time, gave
only moderate or disappointing results involving the acid
chlorides. The amines 8,1 9,5 and 102 were synthesised ac-
cording to literature procedures, the amines 3, 6 and 7
were generated in two steps starting from the allyl alco-
hols 16 and 47: after chlorination with PPh3/CCl4,8 the allyl
chlorides 2 and 5 were treated with pyrrolidine, proline
methylester9 and proline t-butylester,10 respectively, in
Synlett 1999, No. 1, 25–28 ISSN 0936-5214 © Thieme Stuttgart · New Yorkrk

26
S. Laabs et al.
LETTER
Carboxylic acid fluorides are well known in peptide
chemistry. The use of protected a-amino acid fluorides al-
lows amide (dipeptide) and ester formation in high yields
without any racemisation. The acid fluorides have been
described to be stable in presence of tertiary amines, and
the conversion to generate oxazolones was reported to be
slow.12
Indeed, treatment of the allyl amines 3 and 6 to 10 with
carboxylic acid fluorides13 in CH2Cl2 or CHCl3 in pres-
ence of solid Na2CO3 at 0 °C to 23 °C induced neither re-
arrangement nor von Braun degradation suggesting the
low reactivity of such activated carboxylic acids against
tertiary amines. The addition of Me3Al (35 to 100 mol %)
to the mixture started the reaction: Only the rearrange-
ment products were obtained and no allyl halides were
formed pointing out that the competing von Braun degra-
dations were not detected. The yield of rearranged g,d un-
saturated lactams 11 to 16 or amides 17 and 19 to 22 was
significantly increased compared to that of the corre-
sponding acid chloride experiments. It should be empha-
sised that the fluoride rearrangements succeeded with
such allyl amines that failed in the presence of the chlo-
rides (see Table). Furthermore, in contrast to the chloride
series the potential fragmentation of the hypothetical
intermediates formed not any stable ammonium salt (see
Figure) but the allyl amines: a complete conversion of the
reactants could be accomplished adding subsequent
amounts of the carboxylic acid fluorides while running the
reaction. No intermediate work up was necessary.
The rearrangement of the 2-vinyl pyrrolidines 8 and 9
generated the nine-membered ring lactams 11/12 and 13/
14 as mixtures of diastereomers, respectively. In some
cases the determination of the diastereomeric ratio was
pretty difficult because of the permanent conformational
mobility particularly of the cis-products 11 and 14 inhib-
iting a complete separation via HPLC:14, 15 Obviously, the
3,4 cis-arrangement of the substituents allowed the coex-
istence of more than one conformer at room temperature
(planar chirality: equilibrium between pR and pS arrange-
ment of the double bond and amide function with respect
to the ring) effecting the remarkable behaviour during
HPLC separation and the complicated NMR spectra. The
formation of the trans-lactams 13 was characterised by a
conspicuous change of their conformations: right after the
isolation of the product a trans-azoninone with pS ar-
rangement of the double bond was isolated which was ob-
served to undergo a complete conversion to give the
trans-lactam with the olefine in a pR situation;15 no per-
manent mobility was found.
indicating the almost complete simple diastereoselectivity
(internal asymmetric induction) and complete 1,2-asym-
metric inductions (remote stereo control, external asym-
metric induction) effecting the defined generation of a
new C-C bond adjacent to a chiral C-N function as the ma-
jor advantage of this method.3 For structure determination
the amides were cyclised to the corresponding indolizidi-
nones 18.14, 15, 16
The rearrangement of the amines 6 and 7 gave the amides
19 to 22 with a high internal diastereoselectivity, respec-
tively, but the external asymmetric induction seemed to be
low. The d.r. was found to be about 2 : 1 (according to
NMR data) and the diastereomers 19/20 and 21/22 could
not be separated by means of HPLC. The relative configu-
rations of the stereogenic centres were proved after dias-
tereoselective iodo lactonisation17 to the corresponding
scalemic lactones 23 and 24 (< 10 %).14, 15
Obviously, the originally postulated reaction pathway of
the aza-Claisen rearrangements employing the chlorides
should be revised (Figure): In the presence of an acid
chloride the acylammonium salt was immediately formed
after the addition of an allyl amine, the reaction already
proceeded and the subsequent addition of Me3Al partly
suppressed the side reactions to optimise the process. In
contrast, in the presence of the acid fluorides no related
acylammonium fluorides could be detected, and no reac-
Initial experiments to determine the 1,4 chirality transfer
were carried out rearranging allyl amine 10: the trans-lac-
tams 15 were generated diastereoselectively, until now, a
cis-lactam 16 could only be isolated by the reaction of
chloroacetyl chloride as the minor compound (entry e).2,
14, 15
The aza-Claisen rearrangement of allyl amine 3 led to a
single amide 17. No minor diastereomers were isolated,
Synlett 1999, No. 1, 25–28 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Zwitterionic Aza-Claisen Rearrangement: Reaction of Carboxylic Acid Fluorides with N-Allyl Amines
27
(5 x 20 mL) and the combined organic layers were dried
(MgSO4). The solvent was removed and the crude mixture
of diastereomeric amides was purified by column chro-
matography. If necessary, diastereomers were separated
via HPLC or column chromatography on silica gel.
Acknowledgement
This work was supported by the DFG.
References and Notes
(1) Diederich, M.; Nubbemeyer, U. Angew. Chem. 1995, 107,
1095; Angew. Chem., Int. Ed. Engl. 1995, 34, 1026. Diederich,
M.; Nubbemeyer, U. Chem. Eur. J. 1996, 2, 894.
(2) Sudau, A.; Nubbemeyer, U. Angew. Chem. 1998, 110, 1178;
Angew. Chem., Int. Ed. Engl. 1998, 37, 1140.
(3) Nubbemeyer, U. J. Org. Chem. 1996, 61, 3677.
(4) Cooley, J. H.; Evain, E. J. Synthesis 1989, 1.
(5) Deur, C. J.; Miller, M. W.; Hegedus, L. S. J. Org. Chem. 1996,
61, 2871.
(6) Ito, H.; Ikeguchi, Y.; Taguchi, T.; Hanzawa, Y.; Shiro, M. J.
Am. Chem. Soc. 1994, 116, 5469. Ibuka, T.; Taga, T.; Ha-
bashita, H.; Nakai, K.; Tamamura, H. J. Org. Chem. 1993, 58,
1207.
(7) Nakai, T.; Setoi, H.; Kageyama, Y. Tetrahedron Lett. 1981,
22, 4079.
(8) Aneja, R.; Davies, A. P.; Knaggs, J. A. Tetrahedron Lett.
1974, 67.
(9) Zadel, G.; Breitmaier, E. Chem. Ber. 1994, 127, 1323.
(10) Rippberger, H.; Schreiber, K.; Faust, J. J. Prakt. Chem. 1984,
326, 266.
(11) Getti, R. G. P.; Larsson, A. L. E.; Bäckvall, J.-E. J. Chem.
Soc., Perkin Trans I 1997, 577
(12) Granitza, D.; Beyermann, M.; Wenschuh, H.; Haber, H.;
Carpino, L. A.; Truran, G. A.; Bienert, M. J. Chem. Soc.,
Chem. Commun. 1995, 2223. Carpino, L. A.; Mansour, E.-S.
M. E.; El-Faham, A. J. Org. Chem. 1993, 58, 4162. Carpino,
L. A.; Sadat-Aalaee, D.; Chao, H.-G.; DeSelms, R. H. J. Am.
Chem. Soc. 1990, 112, 9651.
(13) We prepared the carboxylic acid fluorides according to Olah,
G. A.; Nojima, M.; Kerekes, I. Synthesis 1978, 487. Olah, G.;
Kuhn, S.; Beke, S. Chem. Ber. 1956, 89, 862.
tion occurred in the absence of Lewis acid. Only the addi-
tion of Me3Al induced the rearrangement, implying either
the passing through an acylammonium salt - Lewis acid
complex with a very short half lifetime or the direct for-
mation of the zwitterionic intermediate as a result of a nu-
cleophilic attack of the amine on a pre-formed ketene-
Lewis acid-complex. Furthermore, the potential forma-
tion of a stable Al-F bond18 should eliminate the nucleo-
phile F- as a latent nucleophile thus suppressing efficiently
the von Braun degradation.
In conclusion, the efficiency of various zwitterionic aza-
Claisen rearrangements profits from the use of carboxylic
acid fluorides: The almost complete suppression of the
competing von Braun degradation and the maintenance of
the stereochemical advantages of the reaction significant-
ly enhance the scope of the process. Further investigations
to employ such rearrangements as key steps in complex
natural product synthesis are in progress.
(14) The relative configuration of all stereogenic centres and, if ne-
cessary, the relative arrangement of trans olefin and amide
function (planar chirality: planar pR and pS arrangements in
the nine-membered ring lactams) was proved by NOE analy-
ses. A minority of conformers (pR or pS) of nine-membered
ring lactams could not be determined undoubtedly because of
higher order NMR spectra.
Standard procedure for the zwitterionic aza-Claisen
rearrangement: Under argon, dry Na2CO3 (1.6 g, 11.6
mmol) was suspended in dry CHCl3 (35 mL) and cooled
to 0°C. N-Allyl amine (5 mmol) and acid fluoride (6
mmol) were added subsequently by means of a syringe.
After about 10 min of stirring at 0 °C, a solution of Me3Al
(0.25 mL, 0.51 mmol, 2 M in toluene) was added via sy-
ringe. The mixture was stirred at 0 °C. The reaction was
carefully monitored by TLC analysis. A second volume of
carboxylic acid fluoride and Me3Al was injected if some
allyl amine was detected after 5 h of reaction time. After
5 to 48 h, the reaction was stopped by quenching dropwise
with saturated aqueous NaHCO3 (5 - 10 mL) at 0 °C until
the Al2O3/Na2CO3 precipitated. Then, the organic layer
was decanted, the solid residue was extracted with CH2Cl2
(15) Spectral data: 1H-NMR: 250 MHz, CDCl3, 22°C, TMS, 13C-
NMR: 62.9 MHz, CDCl3, 22°C.
11d (pS-conformation): 1H-NMR: d = 1.2 (t, J = 7.5 Hz, 3 H,
CH3), 1.48 (mc, 1 H, 8-H1), 1.78 (mc, 1 H, 8-H2), 2.04 (mc, 1
H, 7-H1), 2.36 (mc, 1 H, 7-H2), 2.42 (dd, J = 5, 15 Hz, 1 H, 9-
H1), 2.80 (dd, J = 10, 15 Hz, 1 H, 9-H2), 3.82 (dd, J = 3.8, 11.3
Hz, 1 H, 4-H), 3.86 (d, J = 15 Hz, 1 H, CH2Ph), 4.18 (mc, 2 H,
OCH2), 5.10 (d, J = 3.8 Hz, 1 H, 3-H), 5.28 (d, J = 15 Hz, 1 H,
CH2Ph), 5.64 (ddd, J = 3.8, 11.3, 16.3 Hz, 1 H, 6-H), 6.20 (dd,
J = 11.3, 16.3 Hz, 1 H, 5-H), 7.06 - 7.40 (m, 10 H, Ph). 13C-
NMR: d = 13.9 (CH3), 26.0 (8-C), 31.4 (7-C), 45.5 (9-C), 47.9
(4-C), 48.5 (CH2Ph), 59.4 (3-C), 61.2 (OCH2), 126.4, 126.7,
127.2, 127.4, 128.2, 128.5, 128.6 (Ar-CH, C-6), 134.4 (C-5),
136.0, 137.3 (Ar-C), 172.4, 173.5 (C=O). 12d: 1H-NMR: d =
0.9 (t, J = 7.5 Hz, 3 H, CH3), 1.72 (mc, 1 H, 8-H1), 1.92 - 2.24
(m, 2 H, 8-H2, 7-H1), 2.44 (mc, 1 H, 7-H2), 3.12 (dd, J = 5, 13.8
Synlett 1999, No. 1, 25–28 ISSN 0936-5214 © Thieme Stuttgart · New York

28
S. Laabs et al.
LETTER
Hz, 1 H, 9-H1), 3.76 - 3.88 (m, 4 H, 4-H, OCH2, 9-H2), 3.92
(d, J = 15 Hz, 1 H, CH2Ph), 4.14 (d, J = 11.3 Hz, 1 H, 3-H),
5.36 (d, J = 15 Hz, 1 H, CH2Ph), 5.64 (ddd, J = 3.8, 10, 15 Hz,
1 H, 6-H), 5.84 (dd, J = 9.5, 15 Hz, 1 H, 5-H), 7.08 (mc, 2 H,
Ph), 7.26 (mc, 6 H, Ph), 7.4 (mc, 2 H, Ph). 13C-NMR: d = 13.6
(CH3), 26.8 (8-C), 31.2 (7-C), 44.5 (9-C), 47.2 (CH2Ph), 51.9
(4-C), 55.5 (3-C), 60.4 (OCH2), 127.1, 127.2, 127.8, 128.4,
129.6 (Ar-CH), 131.2 (C-5), 131.7 (C-6), 137.1, 137.6 (Ar-C),
172.1, 172.6 (C=O). 13d (pR-conformation): 1H-NMR: d
=1.03 (d, J = 6.3, 3 H, CH3), 1.49 (mc, 1 H, 8-H1), 1.93 - 2.07
(m, 2 H, 7-H1, 8-H2), 2.33 (mc, 1 H, 7-H2), 2.86 (qid, J = 6.3,
10 Hz, 1 H, 4-H), 3.02 (dd, J = 2.5, 16 Hz, 1 H, 9-H1), 3.67 (d,
J = 10 Hz, 1 H, 3-H), 4.02 (mc, 1 H, 9-H2), 4.03 (d, J = 15 Hz,
1 H, CH2Ph), 5.21 (d, J = 15, 1 H, CH2Ph), 5.71 (ddd, J = 3,
11.3, 16.3 Hz, 1 H, 6-H), 5.93 (dd, J = 6.3, 16.3 Hz, 1 H, 5-H),
7.13 - 7.25 (m, 6 H, Ph), 7.30 (t, br, J = 7.5 Hz, 2 H, Ph), 7.42
(d, br, J = 7.5 Hz, 2 H, Ph). (pS-conformation): d = 0.83 (d, J
= 6.5 Hz, 3 H, CH3), 1.63 (mc, 1 H, 8-H1), 1.99 (mc, 1 H, 8-
H2), 2.06 (mc, 1 H, 7-H1), 2.36 (mc, 1 H, 7-H2), 2.93 (mc, 1 H,
4-H), 3.01 (dd, J = 5, 13.8 Hz, 1 H, 9-H1), 3.58 (d, J = 10 Hz,
1 H, 3-H), 3.76 (dd, J = 10, 13.8 Hz, 1 H, 9-H2), 3.86 (d, J =
15 Hz, 1 H, CH2Ph), 5.35 (d, J = 15 Hz, 1 H, CH2Ph), 5.42 (dd,
J = 9.5, 16.3 Hz, 1 H, 5-H), 5.51 (ddd, J = 3.8, 10.5, 16.3 Hz,
1 H, 6-H), 7.03 (d, br, J = 7.5 Hz, 2 H, Ph), 7.17 (mc, 4 H, Ph),
7.29 (t, br, J = 7.5 Hz, 2 H, Ph), 7.38 (d, br, J = 7.5 Hz, 2 H,
Ph). 14d: 1H-NMR: d = 1.28 (d, J = 7 Hz, 3 H, CH3), 1.76 (mc,
1 H, 8-H1), 2.02 (mc, 1 H, 8-H2), 2.14 (mc, 1 H, 7-H1), 2.46
(mc, 1 H, 7-H2), 2.82 (mc, 1 H, 4-H), 3.10 (dd, J = 5, 15 Hz, 1
H, 9-H1), 3.72 (dd, J = 9.5, 15 Hz, 1 H, 9-H2), 3.98 (d, J = 15
Hz, 1 H, CH2Ph), 4.15 (d, J = 1.3 Hz, 1 H, 3-H), 5.42 (d, J =
15 Hz, 1 H, CH2Ph), 5.60 (ddd, J = 4, 10.5, 15 Hz, 1 H, 6-H),
6.00 (dd, J = 5.5, 15 Hz, 1 H, 5-H), 7.10 - 7.38 (m, 8 H, Ph),
7.56 (mc, 2 H, Ph). 15d: 1H-NMR: d = 0.02 (s, 3 H, H3CSi),
0.05 (s, 3 H, H3CSi), 0.84 (s, 9 H, t-BuSi), 2.08 (ddd, J = 8, 10,
10 Hz, 1 H, 7-H1), 2.50 (dd, J = 5, 12 Hz, 1 H, 4-H1), 2.75 (mc,
1 H, 7-H2), 2.81 (ddd, J = 12, 12, 12 Hz, 1 H, 4-H2), 3.04 (d, J
= 13, 1 H, 9-H1), 3.84 (dd, J = 2, 12 Hz, 1 H, 3-H), 3.95 - 4.15
(m, 3 H, 8-H, 9-H2, CH2Ph), 5.20 (d, J = 16, 1 H, CH2Ph), 5.36
(ddd, J = 4, 12, 16 Hz, 1 H, 6-H), 5.84 (ddd, J = 5, 11, 16 Hz,
1 H, 5-H), 7.20 - 7.30 (m, 10 H, Ph). 17d: 1H-NMR (500 MHz,
C6D6): d = 1.17 (mc, 4 H; ring-CH2), 1.34 (mc, 3 H; 32-H, 41-
H, 42-H), 1.48 (mc, 10 H; 31-H, t-Bu), 2.95 (mc, 1 H; 2’-H),
3.24 (mc, 4 H; ring-CH2N), 3.36 (mc, 2 H; 5-H), 3.93 (mc, 1 H;
2-H), 4.50 (mc, 1 H; 2’-H), 5.08 (d, J = 9 Hz, 1 H; vinyl-CH21),
7.07 (mc, 1 H; Ph), 7.19 (mc, 2 H; Ph), 7.91 (mc, 2 H; Ph). 13C-
NMR (67.9 MHz, C6D6): d = 24.0, 24.2 (ring-CH2), 25.9.(4-
C), 28.6 (t-Bu-CH3), 33.1 (3-C), 45.8, 46.4 (ring-CH2N), 47.4
(5-C), 53.4 (1’-C), 54.4 (2’-C), 57.8 (2-C), 78.2 (O-C), 118.2
(vinyl-CH2), 127.2, 128.6, 130.3 (Ar-CH), 137.7 (vinyl-CH),
139.4 (Ar-C), 155.2, 170.9 (C=O). 17f: 1H-NMR (500 MHz,
C6D6): d = 1.43 (mc, 13 H; 41-H, t-Bu, ring-CH2), 1.63 (mc, 2
H; 42-H, ring-CH2), 1.74 (mc, 2 H; 3-H), 2.90 (mc, 1 H; 1’-H),
3.08 (mc, 1 H; 51-H), 3.21 (mc, 1 H; ring-CH2N), 3.35 (mc, 4
H; 52-H, ring-CH2N), 4.36 (mc, 1 H; 2-H), 4.55 (mc, 3 H; 2’-
H, OCH2Ph), 4.95 (d, J = 9 Hz, 1 H; vinyl-CH2), 5.06 (d, J =
17 Hz, 1 H; vinyl-CH2), 5.79 (mc, 1 H; vinyl-CH), 7.11 (mc, 1
H; Ph), 7.19 (mc, 2 H; Ph), 7.38 (mc, 2 H; Ph).13C-NMR (67.9
MHz, C6D6): d = 23.6, 23.8 (ring-CH2), 26.4.(4-C), 28.6 (t-
Bu-CH3), 31.1 (3-C), 45.8, 46.0 (ring-CH2N), 47.5 (5-C), 53.2
(1’-C), 58.2 (2-C), 72.0 (OCH2Ph), 78.6 (O-C), 81.3 (2’-C),
118.6 (vinyl-CH2), 127.6, 128.4, 130.6 (Ar-CH), 135.1 (vinyl-
CH), 138.8 (Ar-C), 155.3, 169.2 (C=O). 19/20e (major com-
pound): 1H-NMR: d = 1.84-2.28 (m, br, 4 H, ring-CH2), 3.42-
3.62 (m, br, 2 H, ring-CH2N), 3.68 (s, 3 H, OCH3), 3.94 (dd, J
= 7.5, 10 Hz, 1 H, CHAr), 4.42 (d, J = 10 Hz, 1 H, CHCl), 4.44
(dd, J = 3.5, 7 Hz,1 H, ring-CHN), 5.04 (dd, J = 8, 15 Hz, 2 H,
vinyl-CH2), 5.75-5.95 (m, br, 1 H, vinyl-CH), 5.88 (s, 2 H,
OCH2O), 6.61 (d, br, J = 8 Hz ,1 H, ArCH), 6.67 (s, 1 H,
ArCH), 6.74 (d, br, J = 8 Hz ,1 H, ArCH). 13C-NMR: d = 24.6,
28.9 (ring-CH2), 47.0 (ring-CH2N), 52.3 (OCH3), 52.3 (CH-
Cl), 57.6 (ring-CHN), 59.1 (CHAr), 101.1 (OCH2O), 108.3,
108.9, 118.1 (Ar-CH), 118.3 (vinyl-CH2), 122.0 (Ar-C), 133.1
(Ar-C), 136.6 (vinyl-CH), 147.8 (Ar-C), 166.0, 171.9 (C=O).
23: 1H-NMR: d = 2.89 (dd, J = 7.8, 10.5 Hz, 1 H, CH2I), 3.20
(dd, J = 6.6, 10.5 Hz, 1 H, CH2I), 3.87 (dd, J = 3, 6 Hz, 1 H,
4-H), 4.58 (d, J = 3 Hz, 1 H, 3-H), 5.19 (td, br, J = 6, 7.8 Hz,
1 H, 5-H), 6.00 (s, 2 H, OCH2O), 6.64 (d, br, J = 9 Hz, 1 H,
Ar-CH), 6.66 (s, 1 H, Ar-CH), 6.81 (d, br, J = 9 Hz, 1 H, Ar-
CH). 13C-NMR: d = 4.1 (CH2I), 53.8 (4-C), 55.4 (3-C), 81.4
(5-C), 101.6 (OCH2O), 108.2, 109.0, 121.6 (Ar-CH), 126.6,
148.0, 148.48 (Ar-C), 171.1 (C=O).
(16) Mulzer, J.; Shanyoor, M. Tetrahedron Lett. 1993, 34, 6545.
(17) Tamaru, Y.; Mizutani, M.; Furukawa, Y.; Kawamura, S.; Yo-
shida, Z.; Yanagi, K.; Minobe, M. J. Am. Chem. Soc. 1984,
106, 1079.
(18) Energy of Al-X bonds: Al-F: 464 kJmol-1, Al-Cl: 233 kJmol-1
in: Gmelin, Vol. 35B: Aluminium., Pietsch, E. Ed., VCH,
Weinheim, Berlin 1934, 158 (F), 184 (Cl).
2
5.17 (d, J = 17 Hz, 1 H; vinyl-CH2 ), 6.03 (mc, 1 H; vinyl-CH),
Synlett 1999, No. 1, 25–28 ISSN 0936-5214 © Thieme Stuttgart · New York