Electrogenerated Superoxide-Activated Carbon Dioxide. A New Mild and Safe Approach to Organic Carbamates

Article abstract of DOI:10.1021/jo970308h

The electrochemical reduction of O₂ (E = -1.0 V vs SCE) in dipolar aprotic solvents in the presence of CO₂ gave a carboxylating reagent (O₂·-/CO₂) able to convert amines and different types of their derivatives into carbamates. Primary and secondary aliphatic and aromatic amines were converted into the corresponding ethyl carbamates by the addition of EtI to the carbamate anions generated in the first step of the reactions. The yields were dependent on the nucleophilicity of the nitrogen atom ω-Bromoethyl- and propylamine gave 2-oxazolidinone and tetrahydro-l,3-oxazm-2-one in moderate yields. N-Acyl or N-(alkoxycarbonyl)alkylamines bearing a leaving group at the β position of the alkyl substituent were converted into 3-substituted-2-oxazolidinones in high yields. By using chiral substrates, enantiopure 3-alkoxycarbonyl(or acyl)-4-substituted oxazolidin-2-ones (70-85% isolated yields) were obtained. This represents a new mild and safe route to these important auxiliaries for asymmetric synthesis. Some limitations of the process are also evidenced and accounted for.

Full text of DOI:10.1021/jo970308h

6754
J . Org. Chem. 1997, 62, 6754-6759
Electr ogen er a ted Su p er oxid e-Activa ted Ca r bon Dioxid e. A New
Mild a n d Sa fe Ap p r oa ch to Or ga n ic Ca r ba m a tes
Maria Antonietta Casadei, Franco Micheletti Moracci,* and Giovanni Zappia
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Universita` di Roma
“La Sapienza”, P.le Aldo Moro 5, I-00185 Roma, Italy
Achille Inesi* and Leucio Rossi
Dipartimento di Chimica, Ingegneria Chimica e Materiali, Universita` dell’Aquila,
I-67040 Monteluco di Roio, L’Aquila, Italy
Received February 18, 1997X
The electrochemical reduction of O2 (E ) -1.0 V vs SCE) in dipolar aprotic solvents in the presence
of CO2 gave a carboxylating reagent (O2•-/CO2) able to convert amines and different types of their
derivatives into carbamates. Primary and secondary aliphatic and aromatic amines were converted
into the corresponding ethyl carbamates by the addition of EtI to the carbamate anions generated
in the first step of the reactions. The yields were dependent on the nucleophilicity of the nitrogen
atom. ω-Bromoethyl- and propylamine gave 2-oxazolidinone and tetrahydro-1,3-oxazin-2-one in
moderate yields. N-Acyl or N-(alkoxycarbonyl)alkylamines bearing a leaving group at the â position
of the alkyl substituent were converted into 3-substituted-2-oxazolidinones in high yields. By using
chiral substrates, enantiopure 3-alkoxycarbonyl(or acyl)-4-substituted oxazolidin-2-ones (70-85%
isolated yields) were obtained. This represents a new mild and safe route to these important
auxiliaries for asymmetric synthesis. Some limitations of the process are also evidenced and
accounted for.
Organic carbamates,1 including 2-oxazolidinones, are
making use of phosgene or its substitutes. To avoid the
use of such toxic and harmful reagents, much effort has
been devoted to the development of phosgene-free routes
to carbamates, or their precursor.8 The most obvious and
convenient approach to carbamates involves the addition
of a primary or secondary amine to CO2 followed by
alkylation of the intermediate carbamate anion. This
route has been explored by several research groups.9 In
general, the first step has been easily accomplished via
nonassisted (to ionic alkylammonium alkylcarbamates)
or metal-assisted (to metal carbamates) addition of the
amine to CO2. By contrast, alkylation of the carbamate
anion has turned out to be more difficult.9 Ionic carbam-
ates are converted into organic carbamates only in low
to moderate yields under drastic conditions,10a except in
the case of some particular amines.10b The alkylation of
metal carbamates occurs sporadically and is complicated
by the electrophilic attack at carbamic nitrogen to give
N-alkylation products, in contrast to what is observed
with acylating systems.8a,11 Recently, the use of crown
ethers has been introduced in the synthesis of carbam-
ates via amine + CO2 + alkyl halide reaction. In the
presence of the macrocyclic polyether, the yields of
carbamates obtained under mild conditions increase to
acceptable values (typically 35-55%).12 Finally, prelimi-
nary results from our group have shown that carbamates
valuable synthetic intermediates and biologically active
compounds. Their use as protective groups for the amine
function of amino acids has been known in peptide
chemistry since the 30’s2 and up to the present day
endless applications have been described in the litera-
ture.3 Enantiopure 4-substituted 3-acyl-2-oxazolidinones,
also known as “Evans chiral auxiliaries”, were introduced
in the early 80’s and applied with excellent results to
enantioselective aldol condensations, as well as to several
other types of asymmetric reactions.4 Chiral oxazolidi-
nones have also been used to induce asymmetry in
electroorganic synthesis.5 On the basis of their biological
activity, the most extensive use of carbamates is perhaps
as pesticides,6 although some other types of activity are
also important.1,7
The most common syntheses of organic carbamates
involve either the ammonolysis of chloroformates and
carbonates or the addition of alcohols to isocyanates.1,3
All these reagents, in turn, are generally prepared by
X Abstract published in Advance ACS Abstracts, August 1, 1997.
(1) Adams, P.; Baron; F. A. Chem. Rev. 1965, 65, 567-602.
(2) Bergmann, M.; Zervas, K. Ber. Dtsch. Chem. Ges. 1932, 65,
1192-1201.
(3) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic
Synthesis, 2nd ed.; J ohn Wiley and Sons, Inc.: New York, 1991; pp
315-348.
(4) Ager, D. J .; Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96, 835-
875 and references cited therein.
(5) (a) Zielinski, C.; Scha¨fer, H. J . Tetrahedron Lett. 1994, 35, 5621-
5624. (b) Klotz-Berendes, B.; Scha¨fer, H. J .; Grehl, M.; Fro¨hlich, R.
Angew. Chem., Int. Ed. Engl. 1995, 34, 189-191.
(8) (a) Belforte, A.; Belli D’Amico, D.; Calderazzo, F. Chem. Ber.
1988, 121, 1891-1897. (b) Romano, V. Chim. Ind. (Milan) 1993, 75,
303-306 and references cited therein. (c) Ragaini, F.; Cenini, S. Chim.
Ind. (Milan) 1996, 78, 421-427 and references cited therein.
(9) Aresta, M.; Quaranta, M. Proceedings of the International
Conference on Carbon Dioxide Utilization, Bari, Italy, 1993; pp 63-77
and references cited therein.
(10) (a) Yoshida, U.; Ishii, S.; Watanabe, M.; Yamashita, T. Bull.
Chem. Soc. J pn. 1989, 62, 1534-1538 and references cited therein.
(b) Toda, T.; Kitagawa, Y. Angew. Chem., Int. Ed. Engl. 1987, 26, 334-
335.
(6) The Pesticide Manual, 10th ed.; Tomlin, C. D. S., Ed.; Crop
Protection Publication: Farnham, U.K., 1994.
(7) (a) The Pharmacological Basis of Therapeutics, 8th ed.; Goodman,
L., Gilman, A., Rall T. W., Nies, A. S., Taylor, P., Eds.; Pergamon
Press: New York, 1990. (b) Alexander, J .; Bindra, D. S.; Glass, J . D.;
Holahan, M. A.; Renyer, M. L.; Rork, G. S.; Sitko, G. R.; Stranieri, M.
T.; Stupienski, R. F.; Veerapanane, H.; Cook, J . J . J . Med. Chem. 1996,
39, 480-486 and references cited therein. (c) Barbachyn, M. R.;
Hutchinson, D. K.; Brickner, S. J .; Cynamon, M. H.; Kilburn, J . O.;
Klemens, S. P.; Glickman, S. E.; Grega, K. C.; Hendges, S. K.; Toops,
D. S.; Ford, C. W.; Zurenko, G. E. J . Med. Chem. 1996, 39, 680-685.
(11) Aresta, M.; Quaranta, E. Tetrahedron 1991, 47, 9489-9502.
(12) Aresta, M.; Quaranta, E. Tetrahedron 1992, 48, 1515-1530.
S0022-3263(97)00308-3 CCC: $14.00 © 1997 American Chemical Society

Electrogenerated Superoxide-Activated Carbon Dioxide
J . Org. Chem., Vol. 62, No. 20, 1997 6755
Ta ble 1. Ca r boxyla tion of a m in es 1, 3, 5, 7, 10 by
Electr or ed u ction of O2 in th e P r esen ce of CO2 F ollow ed
by Ad d ition of th e Su bstr a tea
Sch em e 1
entry
substrate
products (yield, %)b
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
3a
3b
5
2a (85) [88]
2b (92) [97]
2c (75) [78]
2d (54) [57]
2e (83) [84]
2f (36) [38]
2g (91) [97]
2h (83) [89]
4a (60) [67]
4b (51) [56]
6 (58) [63]
8 (55) [63]
9 (19) [20]
11 (35) [41]
12 (7) [7]
10
11
12
7
13
10
13c
a
MeCN-0.1 M TEAP, Hg cathode, Pt anode, E ) -1.0 V, 3
b
F/mol of substrate passed through the cell. Isolated yields are
given in parentheses, GC (entries 1-4, 7-10) or HPLC yields in
brackets. c Yield not determined.
are also formed in good yields by reaction of the amine
with electrode-activated CO2, followed by alkylation.
However, a strongly negative working potential value (E
) -2.1 V vs SCE) is required in this case.13
followed by treatment with EtI (Table 1, entries 1-8).
The yields of carbamates depend inter alia on the amount
•-
of electricity supplied during the reduction of O2 to O2
.
We have previously shown that the O2•-/CO2 system14
is able to convert NH-protic carboxamides and alcohols,
bearing a leaving group at the ω position, into oxazoli-
dine- or 1,3-oxazine-2,4-diones15a and 1,3-dioxolan- or 1,3-
dioxan-2-ones,15b respectively. The yields are high to
excellent, and very mild conditions are needed. A car-
boxylation-cyclization process involving the formal in-
corporation of CO2 into the substrate has been assumed.15
Unsubstituted alcohols are also converted with moderate
yields to the corresponding ethyl alkyl carbonates after
completion of the reaction by addition of EtI.15b
The highest values were obtained when 3.0 F/mol of
amine were consumed. In addition, the yields were
strongly affected by the nucleophilicity of the amines.
High values (78-97%) were obtained in the case of both
primary and secondary aliphatic amines 1a -c,g,h (Table
1, entries 1-3, 7, 8), whereas aniline 1d was converted
into ethyl carbanilate 2d with only 57% yield (entry 4).
The dependence of the yield values from the lone pair
availability of the nitrogen atom is supported by the clear
substituent effect observed in the case of 4-substituted
anilines 1e,f (entries 5, 6). Furthermore, diphenylamine
1i, where steric hindrance adds to electron delocalization,
is quite unreactive.
Suitable leaving groups at the ω position with respect
to the nitrogen atom allow the formation of cyclic car-
bamates: bromoalkylamines 3a ,b were converted into
2-oxazolidinone 4a and 1,3-oxazin-2-one 4b, respectively
(Table 1, entries 9, 10). The yields were moderate, prob-
ably because of competitive self-alkylation reaction of the
substrate.
Finally, based on the previous work on the carboxyla-
tion of alcohols,15b the potential selectivity of NH- versus
OH-carboxylation was tested by treating amino alcohols
5, 7 and 10 with O2•-/CO2. As a result, the amine group
appeared to be preferably (Table 1, entries 12, 13) or
exclusively (entry 11) carboxylated with respect to the
hydroxy group. The lower reactivity of secondary alco-
hols favored complete selectivity. However, the yields
of N-carboxylated products attained with such substrates
were only moderate.
In this note, the results obtained by reacting several
amines and their derivatives (Schemes 1, 2) with the
system O2•-/CO2 are shown, opening a new, safe, and
high-yield access to both linear and cyclic organic car-
bamates. The reagent has been generated by electrolysis
(divided cell, Hg cathode, Pt anode, room temperature)
of a 0.1 M MeCN solution of TEAP where O2 and CO2
were continuously bubbling into the cathodic compart-
ment. The working potential was sufficiently negative
(E ) -1.0 V vs SCE) to allow the selective reduction of
•-
O2 to O2 with respect to that of CO2. The substrates
were added to the solution at the end of the electrolysis.
The reaction between O2•-/CO2 system and the nitrogen-
containing substrate was considerably influenced by the
reactivity of the NH group as well as by the presence of
suitable leaving groups. The acidity of the CH adjacent
to the nitrogen atom also played a significant role in the
reaction course. The results can be summarized as
follows.
Rea ctivity of O2•-/CO2 ver su s Am in e Der iva tives
(Sch em e 2). The oxazolidin-2-ones 15a -c,e,f,h were
prepared in very high yields by reacting carbamates
14a -h with the carboxylating reagent. The reactions
were independent of the nature of the leaving group
(Table 2, entries 1-8). A much better current efficiency
was obtained in the synthesis of the cyclic N-alkoxycar-
bonyl carbamates: the highest yields were attained by
using 1.2 F/mol of substrate. In analogy to what has been
proposed in the case of ω-haloacylamines,15a the synthesis
of 15 from 14 can be described as a deprotonation-
carboxylation process involving the NH group, followed
Rea ctivity of O2•-/CO2 ver su s Alip h a tic a n d Ar o-
m a tic Am in es a n d Ha loa m in es (Sch em e 1). The
carbamates 2a -h were isolated from solutions containing
the O2•-/CO2 system after addition of amines 1a -h
(13) Casadei, M. A.; Inesi, A.; Micheletti Moracci, F.; Rossi, L. Chem.
Commun. 1996, 2575-2576.
(14) The C2O62- ion has been proposed as the stable product of the
reaction between O2•- and CO2: Roberts, J . L., J r; Calderwood, T. S.;
Sawyer, D. T. J . Am. Chem. Soc. 1984, 106, 4667-4670.
(15) (a) Casadei, M. A.; Cesa, S.; Micheletti Moracci, F.; Inesi, A.;
Feroci, M. J . Org. Chem. 1996, 61, 380-383. (b) Casadei, M. A.; Cesa,
S.; Feroci, M.; Inesi, A.; Micheletti Moracci, F.; Rossi, L. Tetrahedron
1997, 53, 167-176.

6756 J . Org. Chem., Vol. 62, No. 20, 1997
Casadel et al.
Sch em e 2
caused chemical shift nonequivalence (0.3 ppm) of one
of the C5-hydrogens. Applied to oxazolidinone 15c, the
method indicated that the ee was >98%. As evidenced
in the introductory section, chiral oxazolidinones 15 are
very important auxiliaries in asymmetric reactions4,5 and
the present safe, very mild route usefully adds to the
known methods for their synthesis.
Furthermore, N-(2-bromoethyl)acetamides 16a ,b and
pyrrolidone 18 underwent the carboxylation-cyclization
process giving, respectively, 3-acyloxazolidin-2-ones 17
and 3,5-dioxopyrrolo[1,2-c]oxazole 19 in very high yields.
Once again, chiral 19 was obtained from (S)-prolinol
p-toluenesulfonate 18.
It should be noted that the method suffers some
limitations. In particular, if the CH adjacent to the NH
group is activated by the presence of electron-withdraw-
ing groups, the competitive deprotonation of the former
can occur. As an example, N-Boc-3-iodoalanine benzyl
ester 14i was quantitatively converted into N-Boc-dehy-
droalanine benzyl ester 22 (Table 2, entry 9). Therefore,
the â-elimination-assisted deprotonation of the methine
carbon turned out to be selective in this type of substrate.
Furthermore, a strong electron-withdrawing N-substitu-
ent hampers the carboxylation process: amides 20a -c
are converted into aziridines 21a -c while no traces of
oxazolidinones are detectable in the reaction mixture. It
appears that the lower nucleophilicity of the nitrogen
makes the intermolecular reaction no longer competitive
with the intramolecular one, and the cyclization to the
three-membered ring turns out to be a selective process.
Con clu sion s
The electrochemical reduction of O2 (E ) -1.0 V vs
•-
SCE), carried out in the presence of CO2, yields an O2
/
CO2 system which carboxylates substrates containing NH
or OH groups. By taking advantage of this peculiar
reactivity, the synthesis of cyclic and linear carbamates
has been achieved, under very mild conditions. The
reaction of O2•-/CO2 with amines or their derivatives
bearing a leaving group at the appropriate position of
an alkyl residue affords cyclic carbamates according to
a “one-pot, one-step” procedure. On the contrary, the
preparation of linear carbamates, arising from unsub-
stituted amines, requires a further alkylation step of the
first-formed carbamate anion. In any case, high to
excellent yields were observed. The carboxylation-
cyclization of chiral carbamates 14c-h represents a
selective process to prepare enantiopure 4-substituted
oxazolidinones 15c,e,f,h , useful chiral auxiliaries in
asymmetric syntheses. Some limitations of the method
were identified and accounted for.
Ta ble 2. Ca r boxyla tion of Ca r ba m a tes 14 a n d Am id es
16, 18, 20 by Electr or ed u ction of O2 in th e P r esen ce of
CO2 F ollow ed by Ad d ition of th e Su bstr a tea
entry
substrate
products (yield, %)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
14a
14b
14c
14d
14e
14f
14g
14h
14i
16a
16b
18
15a (79) [85]
15b (75) [80]
15c (72) [83]
15c (70) [82]
15e (85) [93]
15f (80) [87]
15f (85) [92]
15h (83) [93]
22 (97) [98]
17a (79) [90]
17b (71) [79]
19 (75) [92]
21a (82) [92]
21b (51) [66]
21c (84) [98]
20a
20b
20c
Exp er im en ta l Section
Gen er a l. The electrochemical apparatus, the cells, and the
reference electrode as well as the mp, IR, NMR, HPLC, and
GC instruments were described elsewhere.15a,16 Unless oth-
erwise stated, column chromatography was performed on 70-
230 mesh SiO2. HPLC analyses were carried out using an RP-
18 column and a CH3CN-H2O mixture in a linear gradient
from 35:65 to absolute CH3CN in 20 min followed by an
a
MeCN-0.1 M TEAP, Hg cathode, Pt anode, E ) -1.0 V, 1.2
b
F/mol of substrate passed through the cell. Isolated yields are
given in parentheses, GC (entry 2) or HPLC yields in brackets.
by a cyclization reaction. Chiral oxazolidin-2-ones
15c,e,f,h have been obtained from chiral substrates 14c-
h . In order to check if racemization occurs during the
carboxylation process, the enantiomeric excess of com-
isocratic step (5 min). The flow rate was 1 mL min-1
. GC
analyses were carried out using a Supelco SPB-5 (30 m, 0.25
mm) column. NMR spectra were acquired on CDCl3 solutions
containing Me4Si as the internal standard. The J values are
1
pound 15c was determined by H NMR spectroscopy in
the presence of Eu(hfc)3. Method development on the
racemic product purposely prepared from (R,S)-14c
showed that a ca. 9:1 Eu(hfc)3/oxazolidinone mixture
(16) Casadei, M. A.; Inesi, A.; J ugelt, A.; Micheletti Moracci, F. J .
Chem. Soc., Perkin. Trans. 1 1992, 2001-2004.

Electrogenerated Superoxide-Activated Carbon Dioxide
reported in hertz. The enantiomeric excess was obtained by
J . Org. Chem., Vol. 62, No. 20, 1997 6757
ter t-Bu tyl N-[(S)-1-ben zyl-2-(tosyloxy)eth yl]ca r ba m a te
(14h ):21 mp 111-115 °C dec (cyclohexane).
1
integrating the relevant peaks in H NMR spectrum recorded
in the presence of Eu(hfc)3, after identification of nonoverlap-
ping peaks of the enantiomers, carried out by using purposely
prepared racemic products. [R]D values were determined by
a Perkin Elmer 243 polarimeter and the c values are given as
g/100 mL. Acetonitrile (MeCN) and tetraethylammonium
perchlorate (TEAP) were purified as already described.16
N-(2-Bromoethyl)amides were prepared from 2-bromoethy-
lamine hydrobromide and the opportune acyl chloride.
N(-2-Br om oeth yl)p h en yla ceta m id e (16a ): mp 84-85 °C
(benzene) [lit.22 mp 84-85 °C]. N-(2-Br om oeth yl)p h en oxy-
a ceta m id e (16b): mp 76-77 °C (cyclohexane); IR (Nujol)
1
3340, 1660, 1530 cm-1; H NMR δ 3.50 (t, J ) 6.0, 2H), 3.75
(q, J ) 6.0, 2H), 4.51 (s, 2H), 6.9-7.2 (m, 4H), 7.2-7.4 (m,
2H); 13C NMR δ 31.89, 40.73, 67.42, 114.85, 122.38, 129.97,
157.22, 168.64. Anal. Calcd for C10H12BrNO2: C, 46.53; H,
4.69; N, 5.43. Found: C, 46.35; H, 4.54; N, 5.30.
N-(2-Br om oeth yl)ben za m id e (20a ): mp 101-103 °C
(benzene) [lit.23 mp 104-105 °C]. (S)-5-[(Tosyloxy)m eth yl]-
2-p yr r olid in on e (18) was prepared as reported in the litera-
ture:24 mp 127-128 °C (EtOH) [lit.25 mp 130 °C].
Rea gen ts. Amines 1a -i, 3a ,b, 5, 7, 10, as well as iodoala-
nine 14i were commercially available (Aldrich). Ben zyl N-(2-
Br om oeth yl)ca r ba m a te (14a ) was prepared from 2-bromo-
ethylamine hydrobromide and benzyl chloroformate: mp 42-
44 °C [lit.17 mp 45 °C]. ter t-Bu tyl N-[2-(Tosyloxy)eth yl]-
ca r ba m a te (14b) was obtained from tert-butyl N-(2-hydroxy-
ethyl)carbamate and tosyl chloride. Column chromatography
of the crude reaction mixture (light petroleum-AcOEt 7:3 as
eluent) gave 14b: mp 47-49 °C (light petroleum); IR (Nujol)
(S)-2-(Tr iflu or oa ceta m id o)-3-p h en ylp r op yl m esyla te
(20b) was prepared by standard procedure from the corre-
sponding hydroxy derivative obtained as described.26
1
3410, 1710, 1600, 1510 cm-1; H NMR δ 1.40 (s, 9H), 2.45 (s,
3H), 3.3-3.5 (m, 2H), 4.18 (t, J ) 5.0, 2H), 4.7-5.1 (br s, 1H),
7.3-7.5 (m, 2H), 7.7-7.9 (m, 2H); 13C NMR δ 21.82, 28.45,
39.90, 69.63, 79.97, 128.27, 130.14, 132.76, 145.23, 155.79.
Anal. Calcd for C14H21NO5S: C, 53.32; H, 6.71; N, 4.44.
Found: C, 53.13; H, 6.59; N, 4.33.
20b: mp 150-152 °C (benzene); [R]21 ) -13.3 (c ) 2.3,
D
MeOH); IR (Nujol) 3310, 1700, 1560 cm-1; 1H NMR δ 2.95 (dd,
J ) 14.0, 8.0, 1H), 3.01 (dd, J ) 14.0, 7.0, 1H), 3.03 (s, 3H),
4.20 (dd, J ) 11.0, 5.0, 1H), 4.34 (dd, J ) 11.0, 4.0, 1H), 4.38-
4.48 (m, 1H), 6.69 (br s, 1H), 7.1-7.4 (m, 5H); 13C NMR δ 36.48,
37.63, 50.77, 68.27, 114.68, 127.54, 129.08, 129.14, 135.40,
157.14. Anal. Calcd for C12H14F3NO4S: C, 44.31; H, 4.34; N,
4.31. Found: C, 44.45; H, 4.41; N, 4.20.
Compounds 14c-h were prepared according to standard
procedures3 from the corresponding N-protected amino alco-
hols. With the exception of (S)-2-amino-3-phenylpropan-1-ol
which was purchased by Fluka, the N-protected amino alcohols
were prepared from the respective N-protected amino acids
according to the literature.18 Ben zyl N-[(S)-4-m eth yl-1-
(tosyloxy)p en ta n -2-yl]ca r ba m a te (14c): mp 94-95 °C (cy-
N-(S)-(1-Br om o-3-p h en ylp r op -2-yl)-4-t olu en esu lfon a -
m id e (20c) was prepared according to the literature:27 mp
118-120 °C (cyclohexane-acetone) [lit.27 mp 120-122 °C).
Electr och em istr y. The electrolyses were carried out at
-1.0 V vs SCE in 0.1 M MeCN solution of TEAP (40 mL),
where O2 and CO2 were simultaneously bubbling. At the end
of the electrolysis, N2 was flowing through the solution for 5
min, and the substrate (2 mmol) was added. In the case of
linear carbamates, a fivefold molar excess of EtI was added
60 min after the current was switched off. The solution was
stirred overnight at rt, a sample (2 mL) was taken off for HPLC
or GC analyses, and the solvent was removed under reduced
pressure from the remaining solution. The residue was
extracted with Et2O (5 × 30 mL); H2O (100 mL) was added to
the insoluble portion in ether, and the mixture was extracted
with CHCl3 (AcOEt for the mixture from 18) (3 × 50 mL). The
extracts were dried (Na2SO4), and the solvent was evaporated
under reduced pressure. The residues were analyzed by IR,
1H NMR, and TLC and combined if they had the same
composition. Column chromatography of the mixtures and/
or crystallization of the residues allowed the isolation of the
single components that were identified by comparison with
authentic samples or fully characterized.
clohexane); [R]21 ) -20.3 (c ) 3.1, CHCl3); IR (Nujol) 3300,
D
1710, 1690, 1600, 1540 cm-1; 1H NMR δ 0.85 (d, J ) 6.5, 6H),
1.2-1.4 (m, 2H), 1.4-1.6 (m, 1H), 2.45 (s, 3H), 3.8-4.1 (m,
3H), 4.80 (br s, 1H), 5.08 (s, 2H), 7.2-7.4 (m, 2H), 7.38 (s, 5H),
7.7-7.9 (m, 2H); 13C NMR δ 21.84, 22.16, 22.98, 24.67, 40.18,
48.44, 66.98, 71.91, 128.14, 128.35, 128.73, 130.12, 132.71,
136.44, 145.19, 155.83. Anal. Calcd for C21H27NO5S: C, 62.20;
H, 6.71; N, 3.45. Found: C, 61.96; H, 6.65; N, 3.27.
Ben zyl N-[(S)-4-m eth yl-1-(m esyloxy)p en ta n -2-yl]ca r -
ba m a te (14d ): mp 57-59 °C (light petroleum); [R]21D ) -31.0
(c ) 4.0, CHCl3); IR (Nujol) 3390, 1700, 1530 cm-1; 1H NMR δ
0.85 (d, J ) 6.5, 6H), 1.2-1.4 (m, 2H), 1.4-1.6 (m, 1H), 2.93
(s, 3H), 3.9-4.3 (m, 3H), 4.95 (br s, 1H), 5.08 (s, 2H), 7.33 (s,
5H); 13C NMR δ 22.08, 23.09, 24.70, 37.33, 40.09, 48.64, 67.03,
71.49, 128.26, 128.37, 128.71, 136.43, 156.01. Anal. Calcd for
C15H23NO5S: C, 54.69; H, 7.04; N, 4.25. Found: C, 54.80; H,
6.95; N, 4.08. Eth yl (S)-4-[(ben zyloxyca r bon yl)a m in o]-5-
(tosyloxy)va ler a te (14e): mp 85-87 °C (cyclohexane); [R]21
D
) -15.6 (c ) 2.8, MeOH); IR (Nujol) 3350, 1730, 1690, 1600,
1
1540 cm-1; H NMR δ 1.20 (t, J ) 7.1, 3H), 1.83 (dt, J ) 7.4,
The isolated and HPLC or GC yields are reported in Tables
1 and 2.
Electr oca r boxyla tion of 1. 3 F/mol of amine was em-
ployed. Carbamates 2 were isolated after column chromatog-
raphy (eluent given in parentheses) of the residue of the
ethereal extracts.
7.0, 2H), 2.35 (t, J ) 7.4, 2H), 2.40 (s, 3H), 3.9-4.2 (m, 5H),
5.10 (s, 2H), 5.0-5.2 (br s, 1H), 7.3-7.5 (m, 2H), 7.35 (s, 5H),
7.7-7.9 (m, 2H); 13C NMR δ 14.33, 21.83, 26.35, 30.71, 49.92,
60.87, 67.04, 71.33, 128.13, 128.36, 128.71, 130.15, 132.51,
136.32, 145.30, 155.93, 173.04. Anal. Calcd for C22H27NO7S:
C, 58.78; H, 6.05; N, 3.12. Found: C, 58.94; H, 5.90; N, 3.02.
Eth yl ben zylca r ba m a te (2a ) (Al2O3; hexane-Et2O 3:2;
Ben zyl N-[(S)-1-b en zyl-2-(t osyloxy)et h yl]ca r b a m a t e
(14f): mp 94-96 °C (AcOEt-cyclohexane); [lit.19 mp 96-97
°C].
265 mg, 85%): mp 43-44 °C [lit.28 mp 44 °C].
E t h yl cycloh exylca r ba m a t e (2b) (Al2O3; hexane-Et2O
3:2; 275 mg, 92%): mp 49-51 °C [lit.29 mp 52 °C].
Ben zyl N-[(S)-1-ben zyl-2-(m esyloxy)eth yl)]ca r ba m a te
(14g):20 mp 108-109 °C (benzene-cyclohexane); IR (Nujol)
3350, 1690, 1540 cm-1 1H NMR δ 2.8-3.0 (m, 2H), 2.94 (s,
;
(21) Van den Broek, L. A. G. M.; Fennis, P. J .; Arevalo, M. A.;
Lazaro, E.; Ballesta, J . P. G.; Lelieveld, P.; Ottenhejm, C. J . Eur. J .
Med. Chem. 1989, 24, 503-510.
3H), 4.05-4.30 (m, 3H), 5.0-5.2 (br s, 1H), 5.07 (s, 2H), 7.1-
7.3 (m, 10H); 13C NMR δ 37.25, 37.38, 51.56, 67.11, 69.73,
127.25, 128.30, 128.44, 128.76, 129.01, 129.42, 136.37, 136.53,
155.87. Anal. Calcd for C18H21NO5S: C, 59.49; H, 5.82; N,
3.85. Found: C, 59.25; H, 5.65; N, 3.72.
(22) Elfeldt, P. Ber. Dtsch. Chem. Ges. 1891, 24, 3218-3228.
(23) Meine, W. H. J . Am. Chem. Soc. 1956, 78, 3708-3710.
(24) Huang, S. B.; Belso, A. S.; Weller, D. D. J . Org. Chem. 1991,
56, 6007-6018.
(25) Hardegger, V. E.; Ott, H. Helv. Chim. Acta 1955, 38, 312-
320.
(17) Katchalski, E.; Ben-Ishai, D. J . Org. Chem., 1950, 15, 1067-
1073.
(26) Curphey, T. J . J . Org. Chem. 1979, 44, 2805-2807.
(27) Barluenga, J .; J imenez, C. N.; Yus, M. J . Chem. Soc. Perkin
Trans. 1 1984, 721-725.
(18) Kokotos, G. Synthesis 1990, 299-301.
(19) Repke, D. B.; Bates, D. K.; Ferguson, W. J . J . Pharm. Sci, 1978,
67, 1167-1168.
(20) Umemura, I.; Miyazaki, N.; Ohigashi, A.; Morinoto, Y. Pept.
Chem. 1991, 28, 277-280; Chem. Abstr. 1991, 115, 117,630z.
(28) Cooper, C. S.; Peyton, A. L.; Weinkam, R. J . J . Org. Chem. 1983,
48, 4116-4118.
(29) Michman, M.; Patai, S.; Wiesel, Y. J . Chem. Soc. Perkin Trans.
1, 1977, 1705-1710.

6758 J . Org. Chem., Vol. 62, No. 20, 1997
Casadel et al.
E t h yl (3-p h en ylp r op yl)ca r b a m a t e (2c) (hexane-Et2O
11: mp 44-46 °C; IR (Nujol) 3440, 3280, 1700, 1610, 1540
cm-1; 1H NMR δ 1.29 (t, J ) 7.1, 3H), 2.5-3.0 (br s, 1H), 4.16
(q, J ) 7.1, 2H), 4.55 (s, 2H), 6.9-7.4 (m, 5H); 13C NMR δ 14.44,
61.19, 64.78, 117.27, 117.88, 121.76, 129.05, 138.15, 142.00,
153.84. Anal. Calcd for C10H13NO3: C, 61.53; H, 6.71; N, 7.17.
Found: C, 61.37; H, 6.64; N, 7.09.
1
7:3; 275 mg, 75%): IR (film) 3330, 1700, 1600, 1530 cm-1; H
NMR δ 1.22 (t, J ) 7.1, 3H), 1.7-1.9 (m, 2H), 2.63 (t, J ) 7.3,
2H), 3.1-3.3 (m, 2H), 4.11 (q, J ) 7.1, 2H), 4.7-4.9 (br s, 1H),
7.1-7.4 (m, 5H); 13C NMR δ 14.56, 31.53, 32.96, 40.46, 60.59,
125.85, 128.24, 128.32, 141.36, 156.65. Anal. Calcd for C12H17
-
NO2: C, 69.54; H, 8.27; N, 6.76. Found: C, 69.46; H, 8.21; N,
6.70.
12: mp 50-52 °C; IR (Nujol) 3350, 1730, 1720, 1620, 1560
1
cm-1; H NMR δ 1.21 (t, J ) 7.0, 3H), 1.22 (t, J ) 7.2, 3H),
Eth yl p h en ylca r ba m a te (2d )30 (hexane-Et2O 4:1; 155 mg,
54%).
4.11 (q, J ) 7.2, 2H), 4.12 (q, J ) 7.0, 2H),5.05 (s, 2H), 6.7-
6.9 (br s, 1H), 6.9-7.4 (m, 4H); 13C NMR δ 14.38, 14.67, 61.40,
64.32, 69.30, 118.43, 118.80, 123.09, 129.43, 136.41, 138.49,
153.76, 155.24. Anal. Calcd for C13H17NO5: C, 58.42; H, 6.41;
N, 5.24. Found: C, 58.30; H, 6.34; N, 5.15.
E t h yl (4-m et h oxyp h en yl)ca r b a m a t e (2e) (hexane-
AcOEt 7:3, 285 mg; 83%): mp 54-56 °C [lit.29 mp 56 °C].
Eth yl (4-cya n op h en yl)ca r ba m a te (2f)31 (hexane-AcOEt;
7:3; 120 mg, 36%): mp 114-116 °C; IR (Nujol) 3300, 2220,
13: 1H NMR δ 1.27 (t, J ) 7.1, 3H), 3.4-3.9 (br s, 2H), 4.21
(q, J ) 7.1, 2H), 5.07 (s, 2H), 6.6-7.3 (m, 4H). 13C NMR δ
14.47, 64.29, 69.63, 114.84, 115.32, 118.49, 129.73, 136.68,
146.82, 155.33.
1
1730, 1590, 1530 cm-1; H NMR δ 1.27 (t, J ) 7.2, 3H), 4.22
(q, J ) 7.2, 2H), 7.22 (br s, 1H), 7.5-7.6 (m, 4H); 13C NMR δ
14.35, 61.72, 105.88, 118.23, 118.93, 133.21, 142.34, 153.03.
Anal. Calcd for C10H10N2O2: C, 63.15; H, 5.30; N, 14.73.
Found: C, 62.99; H, 5.24; N, 14.66.
Electr oca r boxyla tion of 14. 1.2 F/mol of carbamate was
employed. Column chromatography (light petroleum-AcOEt
1:1 as eluent) of the residue of the combined extracts from 14a
gave 3-(ben zyloxyca r bon yl)-2-oxa zolid in on e (15a ) (330
mg, 79%): mp 99-100 °C (EtOH) [lit.36 mp 101-102 °C].
IR and 1H NMR spectra of the residue of the ethereal
extracts from 14b showed the presence as the only compound
of 3-(ter t-bu tyloxyca r bon yl)-2-oxa zolid in on e (15b) (265
mg, 75%): mp 83-85 °C (cyclohexane) [lit.37 mp 85 °C].
Column chromatography (light petroleum-AcOEt 1:1 as
eluent) of the residue of the combined extracts from 14c gave
(S)-3-(ben zyloxyca r bon yl)-4-(2-m eth ylp r op yl)-2-oxa zoli-
d in on e (15c) (380 mg, 72%): mp 55-57 °C (light petroleum);
Eth yl N-ben zyl-N-m eth ylca r ba m a te (2g)32 (hexane-
Et2O 4:1; 310 mg, 91%).
Eth yl N,N-d iben zylca r ba m a te (2h )33 (hexane-Et2O 9:1;
400 mg, 83%).
IR and 1H NMR spectra of the residue of the ethereal extract
from 1i showed the presence of starting material as the only
compound.
Electr oca r boxyla tion of 3. 3 F/mol of bromoamine was
employed. The residue of the combined extracts from the
reaction of 3a was 2-oxazolidinone 4a (100 mg, 60%), as stated
by comparison with an authentic sample (Aldrich).
The residue of the combined extracts from the reaction of
3b was 3,4,5,6-tetr a h yd r o-2H-1,3-oxa zin -2-on e (4b) (98 mg,
51%): mp 80-82 °C (AcOEt) [lit.34 mp 82-83 °C].
Electr oca r boxyla tion of 5, 7 a n d 10. 3 F/mol of amino
alcohol was employed. Column chromatography of the residue
of the combined extracts from 5 (light petroleum-AcOEt 3:2
as eluent) gave eth yl N-(2-h yd r oxy-2-p h en yleth yl)ca r ba m -
a te (6) (230 mg, 58%): mp 85-87 °C (cyclohexane) [lit.35 mp
86-87 °C] and starting 5 (65 mg, 25%). Column chromatog-
raphy of the residue of the combined extracts from 7 (light
petroleum-AcOEt 7:3 as eluent) gave eth yl 2-[(eth oxyca r -
bon yl)a m in o]-2-p h en yleth yl ca r bon a te (9) (100 mg, 19%)
and eth yl (2-h yd r oxy-1-p h en yleth yl)ca r ba m a te (8) (218
mg, 55%).
[R]21 ) +49.2 (c ) 1.4, CHCl3); IR (Nujol) 1820, 1790, 1730
D
1
cm-1; H NMR δ 0.89 (d, J ) 6.0, 3H), 0.93 (d, J ) 6.0, 3H),
1.50-1.80 (m, 3H), 4.06 (dd, J ) 8.0, 2.5, 1H), 4.31 (tdd, J )
8.0, 3.0, 2.0, 1H), 4.37 (t, J ) 8.0, 1H), 5.27 (d, J ) 12.5, 1H),
5.34 (d, J ) 12.5, 1H), 7.35-7.45 (m, 5H); 13C NMR δ 21.48,
23.37, 24.58, 41.88, 53.84, 67.21, 68.56, 128.26, 128.56, 128.60,
134.81, 150.71, 151.83. Anal. Calcd for C15H19NO4: C, 64.97;
H, 6.91; N, 5.05. Found: C, 65.10; H, 7.00; N, 4.96.
Column chromatography of the residue of the combined
extracts from 14d gave 15c (370 mg, 70%).
Column chromatography (CHCl3-AcOEt 9:1 as eluent) of
the combined extracts from 14e gave (S)-3-(ben zyloxyca r bo-
n yl)-4-[2-(eth oxyca r bon yl)eth yl]-2-oxa zolid in on e (15e)
(510 mg, 85%): mp 66-68 °C (cyclohexane); [R]21 ) +37.7 (c
D
1
) 1.9, CHCl3); IR (Nujol) 1810, 1800, 1730 cm-1; H NMR δ
8: mp 79-81 °C (cyclohexane); IR (Nujol) 3380, 3330, 1690,
1550 cm-1; 1H NMR δ 1.21 (t, J ) 7.0, 3H), 2.0-2.4 (br s, 1H),
3.6-3.9 (m, 2H), 4.11 (q, J ) 7.0, 2H), 4.7-4.9 (m, 1H), 5.3-
5.6 (br s, 1H), 7.1-7.5 (m, 5H); 13C NMR δ 14.53, 57.10, 61.20,
66.61, 126.57, 127.85, 128.83, 139.28, 156.71. Anal. Calcd for
C11H15NO3: C, 63.14; H, 7.23; N, 6.69. Found: C, 63.01; H,
7.16; N, 6.58.
9: mp 61-63 °C (light petroleum); IR (Nujol) 3330, 1740,
1690, 1540 cm-1; 1H NMR δ 1.15 (t, J ) 7.0, 3H), 1.22 (t, J )
7.1, 3H), 3.9-4.1 (m, 4H), 4.30 (d, J ) 5.5, 2H), 4.9-5.1 (m,
1H), 5.2-5.4 (br s, 1H), 7.27 (s, 5H); 13C NMR δ 14.46, 14.79,
54.70, 61.71, 64.96, 70.11, 127.59, 129.00, 129.78, 139.45,
156.25, 157.14. Anal. Calcd for C14H19NO5: C, 59.78; H, 6.81;
N, 4.98. Found: C, 59.91; H, 6.73; N, 4.82. Column chroma-
tography of the residue of the combined extracts from 10 (light
petroleum-AcOEt 1:1 as eluent) gave eth yl 3-[(eth oxyca r -
b on yl)a m in o]b en zyl ca r b on a t e (12) (35 mg, 7%), et h yl
N-[3-(h yd r oxym eth yl)p h en yl]ca r ba m a te (11) (130 mg,
35%), starting 10 (35 mg, 15%), and an unresolved fraction
whose 1H NMR spectrum showed the presence of eth yl
3-a m in oben zyl ca r bon a te (13).
1.25 (t, J ) 7.0, 3H), 2.07 (dtd, J ) 14.0, 8.0, 2.5, 1H), 2.10
(dtd, J ) 14.0, 8.0, 4.5, 1H), 2.36 (t, J ) 8.0, 2H), 4.10 (q, J )
7.0, 2H), 4.12 (dd, J ) 8.0, 2.5, 1H), 4.40 (t, J ) 8.0, 1H), 4.44
(tdd, J ) 8.0, 4.5, 2.5, 1H), 5.32 (s, 2H), 7.30-7.45 (m, 5H);
13C NMR δ 14.14, 28.29, 29.23, 54.26, 60.70, 66.77, 68.77,
128.27, 128.60, 128.66, 134.76, 150.80, 151.59, 172.09. Anal.
Calcd for C16H19NO6: C, 59.81; H, 5.96; N, 4.36. Found: C,
59.64; H, 5.84; N, 4.25.
Column chromatography (light petroleum-AcOEt 3:2 as
eluent) of the residue of the ethereal extracts from 14f gave
(S)-3-(ben zyloxyca r bon yl)-4-ben zyl-2-oxa zolid in on e (15f)
(470 mg, 80%): mp 70-71 °C (cyclohexane); [R]21 ) +28.5 (c
D
1
) 2.0, CHCl3); IR (Nujol) 1820, 1800, 1720 cm-1; H NMR δ
2.84 (dd, J ) 13.5, 9.5, 1H), 3.30 (dd, J ) 13.5, 3.5, 1H), 4.14
(dd, J ) 9.0, 3.5, 1H), 4.21 (dd, J ) 9.0, 7.5, 1H), 4.54 (ddt, J
) 9.5, 7.5, 3.5, 1H), 5.35 (s, 2H), 7.10-7.40 (m, 10H); 13C NMR
δ 38.58, 56.17, 65.93, 68.90, 127.52, 128.51, 128.85, 129.12,
129.50, 134.97, 135.06, 150.90, 151.81. Anal. Calcd for C15H19
-
NO4: C, 64.97; H, 6.91; N, 5.05. Found: C, 65.09; H, 6.99; N,
4.92. The residue of the ethereal extracts from 14g (500 mg,
1
85%) was identified as 15f on the basis of its IR and H NMR
spectra.
Column chromatography (light petroleum-AcOEt 1:1 as
eluent) of the residue of the combined extracts from 14h gave
(S)-3-(ter t-b u t yloxyca r b on yl)-4-b en zyl-2-oxa zolid in on e
(30) Torimoto, N.; Shingaki, T..; Nagai, T. Bull. Chem. Soc. J pn.
1978, 51, 2983-2987.
(31) Dicken, C. M.; Lu, F. L.; Nee, M. W.; Bruice, T. C. J . Am.
Chem.Soc. 1985, 107, 5776-5789.
(15h ) (435 mg, 83%): mp 101-103 °C (cyclohexane); [R]21
)
D
+20.8 (c ) 1.2, CHCl3); IR (Nujol) 1800, 1710 cm-1; H NMR
1
(32) Tamura, Y.; Haruta, J .; Okuyama, S.; Kita, Y. Tetrahedron Lett.
1978, 19, 3737-3740.
(33) Braun, J . V. Ber.Dtsch. Chem. Ges. 1903, 36, 2286-2290.
(34) Hall, H. K. J .; Schneider, A. K. J . Am. Chem. Soc. 1958, 80,
6409-6412.
(36) Ben-Ishai, D. J . Am. Chem. Soc. 1956, 78, 4962-4965.
(37) Ishizuka, T.; Kunieda, T. Tetrahedron Lett. 1987, 28, 4185-
4188.
(35) Foglia, T. A.; Swern, D. J . Org. Chem. 1966, 31, 3625-3631.

Electrogenerated Superoxide-Activated Carbon Dioxide
J . Org. Chem., Vol. 62, No. 20, 1997 6759
δ 1.60 (s, 9H), 2.80 (dd, J ) 13.5, 9.5, 1H), 3.30 (dd, J ) 13.5,
3.5, 1H), 4.10 (dd, J ) 9.0, 3.5, 1H) 4.16 (t, J ) 9.0, 1H), 4.46
(tt, J ) 9.5, 3.5 1H), 7.15-7.35 (m, 5H). 13C NMR δ 28.20,
38.90, 56.30, 65.65, 84.23, 127.53, 129.20, 129.53, 135.41,
149.39, 152.28. Anal. Calcd for C18H17NO4: C, 69.44; H, 5.50;
N, 4.50. Found: C, 69.32; H, 5.41; N, 4.40.
13.0, 8.0, 6.0, 1H), 2.72 (br dd, J ) 17.0, 8.0, 1H), 2.84 (ddd, J
) 17.0, 13.0, 8.0, 1H), 4.15 (t, J ) 8.5, 1H), 4.64 (t, J ) 8.5,
1H), 4.72 (qd, J ) 8.5, 6.0, 1H); 13C NMR δ 27.61, 35.71, 56.61,
71.01, 149.68, 171.54. Anal. Calcd for C6H7NO3: C, 51.06;
H, 5.00; N, 9.92. Found: C, 50.94; H, 4.90; N, 9.85.
Cycliza tion of 20. 1.2 F/mol of amide was employed.
Aziridines 21 were isolated after column chromatography
(eluent given in parentheses) of the residue from the combined
extracts.
IR and 1H NMR spectra of the residue of the combined
extracts from 14i showed the presence of N-Boc d eh yd r oa la -
n in e ben zyl ester (22) as the only compound (510 mg, 97%):
IR (film) 3420, 1740, 1720, 1630, 1510 cm-1; H NMR δ 1.40
1-Ben zoyla zir id in e (21a )39 (light petroleum-AcOEt 1:1;
230 mg, 82%).
1
(s, 9H), 5.18 (s, 2H), 5.71 (d, J ) 1.5, 1H), 6.11 (s, 1H), 6.98
(br s, 1H), 7.30 (s, 5H); 13C NMR δ 28.44, 67.83, 80.92, 105.65,
128.41, 128.74, 128.85, 131.52, 135.36, 152.76, 164.09. Anal.
Calcd for C15H19NO4: C, 64.97; H, 6.91; N, 5.05. Found: C,
64.82; H, 6.84; N, 4.96.
(S)-1-(Tr iflu or oa cetyl)-2-ben zyla zir id in e (21b) (CHCl3-
propan-2-ol 95:5; 220 mg, 51%): [R]21 ) -50.3 (c ) 2.3,
D
1
CHCl3); IR (film) 1690, 1610 cm-1; H NMR δ 2.77 (dd, J )
14.0, 8.0, 1H), 3.17 (dd, J ) 14.0, 5.0, 1H), 4.23 (dd, J ) 9.0,
8.0, 1H), 4.44 (t, J ) 9.0, 1H), 4.56-4.66 (m, 1H), 7.20-7.32
(m, 5H); 13C NMR δ 40.64, 67.56, 73.74, 116.33, 126.96, 128.71,
129.21, 136.37, 155.20. Anal. Calcd for C11H10F3NO: C, 57.64;
H, 4.40; N, 6.11. Found: C, 57.46; H, 4.29; N, 5.99.
Electr oca r boxyla tion of 16. 1.2 F/mol of bromoamide
was employed. Column chromatography (light petroleum-
AcOEt 1:1 as eluent) of the residue of the combined extracts
from 16a gave 3-(p h en yla cetyl)-2-oxa zolid in on e (17a ) (285
mg, 79%): mp 56-58 °C [lit.38 mp 55-56 °C].
Column chromatography (light petroleum-AcOEt 3:2 as
eluent) of the residue of the combined extracts from 16b gave
3-(p h en oxya cetyl)-2-oxa zolid in on e (17b) (280 mg, 71%):
mp 93-95 °C [lit.38 mp 95.5-96.5 °C].
1-Tosyl-2-ben zyla zir id in e (21c) (light petroleum-AcOEt
4:1; 460 mg, 84%): mp 90-91 °C [lit.40 mp 92-94 °C].
Ack n ow led gm en t. The authors wish to thank Prof.
G. Delle Monache, Universita` Cattolica del Sacro Cuore,
Roma for the NMR measurements. This work was
supported by research grants from MURST (1995, 60%)
and CNR, Roma, Italy.
Electr oca r boxyla tion of 18. 1.2 F/mol of pyrrolidone was
employed. The residue of the combined extracts from 18 was
(S)-1H,3H-5,6,7,7a -tetr a h yd r o-3,5-d ioxop yr r olo[1,2-c]ox-
a zole (19) (200 mg, 75%): mp 136-138 °C (benzene); [R]21
D
) +12.2 (c ) 9.0, CHCl3); IR (Nujol) 1850, 1800, 1730, 1710
cm-1; 1H NMR δ 2.06 (tt, J ) 13.0, 8.5, 1H), 2.44 (br ddd, J )
J O970308H
(39) Boggs, G. R.; Gerig, J . T. J . Org. Chem. 1969, 34, 1484-1486.
(40) Tseng, C. C.; Terashma, S.; Yiamada, S. I. Chem. Pharm. Bull.
1977, 25, 28-40.
(38) Shibata, J .; Nakamura, K.; Baba, A.; Matsuda, H. Bull. Chem.
Soc. J pn. 1989, 62, 853-859.