Alternate Self-Regeneration of Stereocenters: Enantioselective Generation of a C2-Symmetric Chiral Nitroxide and Its Reduction to the Corresponding, Highly Sterically Hindered Amine

Full text of DOI:10.1021/jo971812p

J . Org. Chem. 1997, 62, 9385-9388
9385
Sch em e 1. En a n tioselective Syn th esis of
C2-Sym m etr ic
(2S,5S)-2,5-Dim eth yl-2,5-d ip h en ylp yr r olid in -1-oxy
Alter n a te Self-Regen er a tion of
Ster eocen ter s: En a n tioselective
Gen er a tion of a C2-Sym m etr ic Ch ir a l
Nitr oxid e a n d Its Red u ction to th e
Cor r esp on d in g, High ly Ster ica lly Hin d er ed
Am in e
Ra d ica l 3
J acques Einhorn,* Cathy Einhorn, Fabien Ratajczak,
Isabelle Gautier-Luneau, and J ean-Louis Pierre
Laboratoire de Chimie Biomime´tique,
LEDSS/ UMR CNRS 5616, Universite´ J . Fourier,
38041 Grenoble, France
Received October 1, 1997
Nitroxides continue to play a central role among
organic stable free radicals. They have been, and are
still, extensively used as spin labels1 and in spin trapping
experiments,2 but many other promising applications
have emerged more recently: they are now studied as
spin sources for the elaboration of organic magnetic
materials,3 as precursors of highly selective oxidants,4 or
as capping agents for the control of “living” free-radical
polymerization processes.5 Chiral nitroxides have at-
tracted a special interest in very recent years due to their
potential applications as enantioselective oxidation cata-
lysts, for the development of paramagnetic chiral liquid
crystals, or in stereoselective coupling reactions with
prochiral radicals.6 Moreover, chiral nitroxides can be
reductively transformed into the corresponding, poten-
tially valuable, chiral amines by very simple and mild
chemical processes.2a In this context, C2-symmetric chiral
nitroxides appear to be valuable synthetic targets, owing
to the well-recognized importance of C2 chiral auxiliaries
in asymmetric synthesis.7 Up to now, although several
C2-symmetric nitroxide have been described in their
racemic form,5c,8a-e examples of optically active C2 ni-
troxides remain scarce. Mu¨llen8f and Sogah5c prepared
racemic trans-2,5-dimethyl-2,5-diphenylpyrrolidin-1-oxy
radical 3. Mu¨llen separated its enantiomers on a half
gram scale by chiral HPLC. However, the absolute
configurations of the stereocenters remained unknown.
We describe herein an enantioselective approach to
nitroxide 3, starting from readily available optically
active trans-2,5-dimethylpyrrolidine (1b) (Scheme 1).
The principle of the synthesis is very simple: C2-
symmetric optically active pyrrolidine 1b, bearing two
equivalent stereogenic centers, was first oxidized into
optically active nitrone 2. The following synthesis uti-
lized the methodology originally developed by Keana8a-d
and also used by Mullen8f and proceeded via two succes-
sive nitrone nucleophilic addition-oxidation sequences.
This method was known as allowing an efficient control
of the relative stereochemistry of the newly created
stereocenters, the nucleophiles being introduced on the
most accessible faces of the intermediate nitrones, i.e.,
in the trans relationship with respect to the bulkiest
substituent. When applied to optically active nitrone 2,
an absolute control of the newly created stereocenters
was performed, generating optically active, C2-symmetric
nitroxide 3. Starting from C2-symmetric pyrrolidine 1,
the whole process can be conceptually related to See-
bach’s general principle of self-regeneration of stereo-
centers (SRS).9 In our case, each stereocenter alterna-
tively plays the role of “chiral memory”, the second one
being destroyed during oxidation into a nitrone. The
remaining stereocenter is, therefore, able to ensure the
absolute stereochemical control of the subsequent nu-
cleophilic addition to this nitrone.
(1) (a) Keana, J . F. W. Chem. Rev. 1978, 78, 37-64. For recent
examples see: (b) Bossmann, S. H.; Ghatlia, N. D.; Ottaviani, M. F.;
Turro, C.; Du¨rr, H.; Turro, N. J . Synthesis 1996, 1313-1319. (c) Ulrich,
G; Turek, P.; Ziessel, R.; De Cian, A.; Fischer, J . Chem. Commun. 1996,
2461-2462.
(2) (a) Aurich, H. G. in Nitrones, Nitronates and Nitroxides; Patai,
S., Rappoport, Z., Eds.; J ohn Wiley & Sons, Inc.: New York, 1989; pp
313-399. For a recent example, see: (b) Sankuratri, N.; J anzen, E.
G.; West, M. S.; Poyer, J . L. J . Org. Chem. 1997, 62, 1176-1178 and
references therein.
(3) See, for example: (a) Chiarelli, R.; Novak, M. A.; Rassat, A.;
Tholence, J . L. Nature 1993, 363, 147-149. (b) Cirujeda, J .; Mas, M.;
Molins, E.; Lanfranc de Panthou, F.; Laugier, J .; Park, J . G.; Paulsen,
C.; Rey, P.; Rovira, C.; Veciana, J . J . Chem. Soc., Chem. Commun.
1995, 709-710. (c) Inoue, K.; Hayamizu, T.; Iwamura, H.; Hashizume,
D.; Onashi, Y. J . Am. Chem. Soc. 1996, 118, 1803-1804.
Improved methods are known for the synthesis of
optically active trans-2,5-dimethylpyrrolidine.10 One of
the most convenient methods, reported by Masamune,11
starts from optically pure (2S,5S)-2,5-hexanediol,12 now
(4) (a) Einhorn, J .; Einhorn, C.; Ratajczak, F.; Pierre, J . L. J . Org.
Chem. 1996, 61, 7452-7454. For a review see: (b) de Nooy, A. E. J .;
Besemer, A. C.; van Bekkum, H. Synthesis 1996, 1153-1174.
(5) (a) Hawker, C. J . J . Am. Chem. Soc. 1994, 116, 11185-11186.
(b) Hawker, C. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 1456-1459.
(c) Puts, R. D.; Sogah, D. Y. Macromolecules 1996, 29, 3323-3325. (d)
Connolly, T. J .; Scaiano, J . C. Tetrahedron Lett. 1997, 38, 1133-1136.
(6) (a) Ma, Z.; Huang, Q.; Bobbitt, J . M. J . Org. Chem. 1993, 58,
4837-4843. (b) Rychnovsky, S. D.; McLernon, T. L.; Rajapakse, H. J .
Org. Chem. 1996, 61, 1194-1195. (c) Tamura, R.; Susuki, S.; Azuma,
N.; Matsumoto, A.; Toda, F.; Kamimura, A.; Hori, K. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 878-879. (d) Tamura, R.; Susuki, S.; Azuma,
N.; Matsumoto, A.; Toda, F.; Ishii, Y. J . Org. Chem. 1995, 60, 6820-
6825. (e) Braslau, R.; Burrill, L. C., II; Mahal, L. K.; Wedeking, T.
Angew. Chem., Int. Ed. Engl. 1997, 36, 237-238.
(8) (a) Lee, T. D.; Birrel, G. B.; Keana, J . F. W. J . Am. Chem. Soc.
1978, 100, 1618-1619. (b) Keana, J . F. W.; Seyedrezai, S. E.; Gaughan,
G. J . Org. Chem. 1983, 48, 2644-2647. (c) Keana, J . F. W.; Cuomo,
J .; Lex, L.; Seyedrezai, S. E. J . Org. Chem. 1983, 48, 2647-2654. (d)
Keana, J . F. W.; Prabhu., V. S. J . Org. Chem. 1986, 51, 4300-4301.
(e) Einhorn, J .; Einhorn, C.; Ratajczak, F.; Pierre, J . L. J . Chem. Soc.,
Chem. Commun. 1995, 1029-1030. (f) Benfaremo, N.; Steenbock, M.;
Klapper, M.; Mu¨llen, K.; Enkelmann, V.; Cabrera, K. Liebigs Ann.
1996, 1413-1415.
(9) Review: Seebach, D.; Sting, A. R.; Hoffmann, M. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2708-2748.
(10) For a review on the synthesis of 2,5-disubstituted pyrrolidines
see: Pichon, M.; Figade`re, B. Tetrahedron: Asymmetry 1996, 7, 927-
964.
(7) Review: Whitesell, J . K. Chem. Rev. 1989, 89, 1581-1590.
S0022-3263(97)01812-4 CCC: $14.00 © 1997 American Chemical Society

9386 J . Org. Chem., Vol. 62, No. 26, 1997
Notes
Sch em e 2. Red u ction of Nitr oxid e 3 to Am in e 4
commercially available. Transformation of the diol into
dimesilate and double nucleophilic displacement with
benzylamine furnishes (2R,5R)-1-benzyl-2,5-dimethylpyr-
rolidine (1a ) with high enantiopurity. In our hands, 1a
proved to be an easy-to-store, protected form of pyrroli-
dine 1b itself: N-debenzylation of 1a to 1b and subse-
quent oxidation of 1b into nitrone 2 has thus been
conducted without the need of the highly volatile 1b to
be isolated. The choice of the proper oxidation method
of 1b into 2 was crucial: oxidation of amines to nitrones
can efficiently be performed with H2O2 catalyzed by
Na2WO4.13 Applied to optically active 1b, this method
gave somewhat erratic results with variable degrees of
racemization of nitrone 2. A better alternative is the
recently described oxidation method using methyltrioxo-
rhenium/urea‚H2O2 complex.14 In this case, the enan-
tiomeric purity of nitrone 2 consistently reflects that of
amine 1a .15 The following synthesis was straightfor-
ward: reaction of optically active nitrone 2 (96% ee) with
phenylmagnesium bromide, at -78 °C, followed by a
reaction sequence similar to that developed by Keana,8a-d
gave nitroxide 3 with an enantiomeric excess of 93%
(measured after column chromatography purification on
silica gel).16,17 The absolute configuration of nitroxide 3
can be correlated to that of the starting amine 1b:
(2R,5R)-2,5-dimethylpyrrolidine furnishes (2S,5S)-2,5-
dimethyl-2,5-diphenylpyrrolidin-1-oxy radical. The enan-
tiomeric purity of nitroxide 3 could be raised from 93%
to 99.8% by two recrystallizations from hexane. This
(Scheme 2). Starting from a sample of 3 with an ee of
99.8%, amine 4 had a specific rotation [R]21 -119.7 (c
D
2.61, EtOAc). Attempts to determine the enantiomeric
purity of this amine directly by chiral HPLC or by using
NMR techniques19 have failed so far. It was, however,
possible to oxidize amine 4 back into nitroxide 3 with
Oxone.20 Recovered nitroxide 3 had an unchanged enan-
tiomeric purity, confirming that, as expected, both reduc-
tion and reoxidation occurred without any loss of enan-
tiomeric purity. Optically active 4 should find interesting
applications, for example, by transformation into its
lithium amide, as a C2-symmetric chiral equivalent of
lithium 2,2,6,6-tetramethylpiperidide (LiTMP).21
Exp er im en ta l Section
Gen er a l Meth od s. (2S,5S)-2,5-Hexanediol, urea‚H2O2 com-
plex, Oxone, and methyltrioxorhenium were purchased from
Aldrich and used without purification. THF was distilled over
sodium/benzophenone prior to use. Infrared spectra were
recorded as liquid fims on NaCl plates or as KBr pellets. 1H
NMR spectra were recorded at 250 MHz and 13C NMR at 62.5
MHz; CDCl3 was used as the solvent. Chiral HPLC was
performed on a Chiracel OD-H column with a UV-vis spec-
trometer (254 nm) as the detector. UV-vis spectra were
recorded in CH2Cl2 solutions in 1 cm quartz cells.
sample had a specific rotation [R]21 -170.5 (c 1.04,
D
EtOAc) and melted at 132.5-133 °C (lit.8f [R]25 174.4 (c
D
0.108, hexane), mp 130 °C). The spectral properties were
in accordance with literature data.8f Optically pure 3 is
thus available from commercial optically active 2,5-
hexanediol without any intermediate enantiomeric en-
richment.
(5R)-3,4-Dih yd r o-2,5-d im eth yl-5H-p yr r ole 1-Oxid e (2).
1a (6.6 g, 34.3 mmol) (96% ee) was dissolved in 15 mL of MeOH.
Pd(OH)2 (2 g) at 20% on carbon was added, and the mixture
was vigorously stirred under H2, at room temperature and
atmospheric pressure, until completion of the reaction (TLC on
alumina; hexane/EtOAc, 1:1) (5-7 h). The reaction mixture was
then filtered on a short path of Celite. Catalyst and Celite were
thorougly washed with MeOH (3 × 5 mL) and the washings
combined with the filtrate. In a separate flask, 0.185 g of
methyltrioxorhenium and 25 g of urea‚H2O2 complex in 5 mL of
MeOH were stirred at room temperature during 10 min and then
cooled to 0 °C. The methanolic solution obtained earlier was
then added under stirring to this reaction mixture, whose color
turned from yellow to dark red. After the mixture has been
stirred for 1 h at 0 °C, followed by 12 h at room temperature,
the solvent was evaporated in vacuo. The yellowish solid residue
was washed with CH2Cl2 (3 × 50 mL). The filtrate was
concentrated to give a yellow oil. This crude product was
purified by column chromatography (silica gel; EtOAc/MeOH,
Nitroxide 3 was next reduced to the corresponding
amine 4. Attempts to perform the reduction by catalytic
hydrogenation using various catalysts were disapointing,
leading to extensive degradation. Gratifingly, reduction
by zinc in aqueous hydrochloric acid18 followed by an
alkaline workup gave amine 4 with a quantitative yield
(11) Short, R. P.; Kennedy, R. M.; Masamune, S. J . Org. Chem. 1989,
54, 1755-1756.
(12) (2S,5S)-2,5-Hexanediol is conveniently obtained by bakers’ yeast
reduction of 2,5-hexanedione: Lieser, J . K. Synth. Commun. 1983, 13,
765-767. For
a recent synthesis of (2R,5R)-2,5-hexanediol from
mannitol, see: Saravanan, P.; Raina, S.; Sambamurthy, T.; Singh, V.
K. J . Org. Chem. 1997, 62, 2669-2670.
8:2) to afford 2 g (51%) of pure nitrone 2: [R]21 +13.6 (c 1.07,
D
EtOAc), ee ) 96%.15 Spectroscopic data are in accordance with
(13) (a) Murahashi, S. I.; Mitsui, H.; Shiota, T.; Tsuda, T.; Watanabe,
S. J . Org. Chem. 1990, 55, 1736-1744. (b) Murahashi, S I.; Shiota,
T.; Imada, Y. Org. Synth. 1991, 70, 265-271.
(14) (a) Murray, R. W.; Iyanar, K.; Chen, J .; Wearing, J . T. J . Org.
Chem. 1996, 61, 8099-8102. (b) Goti, A.; Nanelli, L. Tetrahedron Lett.
1996, 37, 6025-6028.
those of the literature concerning the racemic compound.22
(2S,5S)-2,5-Dim eth yl-2,5-d ip h en ylp yr r olid in -1-oxy Ra d i-
ca l (3). Nitrone 2 (2 g, 17.6 mmol) (96% ee) was dissolved in
10 mL of anhydrous THF, under argon, and cooled at -78 °C.
To this was added a solution of PhMgBr in THF (1 M, 35 mmol,
35 mL). The temperature was raised slowly to room tempera-
ture, and stirring was maintained overnight. The reaction
(15) The enantiomeric purity of optically active nitrone 2 has been
estimated by 1H NMR at 200 MHz by adding 3 equiv of enantiomeri-
cally pure 2,2′-dihydroxy-1,1′-binaphthyl to a diluted solution of nitrone
2 in CDCl3. Effective splitting of the methyl singlet at 2.04 ppm was
observed. See: Toda, F.; Mori, K.; Okada, J .; Node, M.; Itoh, A.;
Oomine, K.; Fuji, K. Chem. Lett. 1988, 131-134.
(19) Parker, D. Chem. Rev. 1991, 91, 1441-1457.
(20) See: Brik, M. E. Tetrahedron Lett. 1995, 36, 5519-5522. Brik
claimed in situ generated dimethyldioxirane to be the true oxidant in
his procedure, as acetone was used as a cosolvent. We have, however,
found that when acetone was replaced by ethanol or methanol very
similar results were observed, suggesting a more direct involvment of
Oxone.
(21) For recent examples of C2-symmetric amines, see: Woltersdorf,
M.; Kranich, R.; Schmalz, H. G. Tetrahedron 1997, 53, 7219-7230.
For applications of C2-symmetric amines in synthesis see references
therein.
(16) Enantiomeric composition of the optically active nitroxide has
been determined by HPLC on a Chiracel OD-H column, elution: iPrOH/
hexane (1/9), 0.5 mL min-1
.
(17) When the same sequence was performed with (4-tert-butylphen-
yl)magnesium bromide on another sample of nitrone 2 with ee ) 98%,
a 79% ee of the corresponding nitroxide was obtained. Benzylmagne-
sium bromide gave the dibenzyl nitroxide with an ee of only 7%,
starting from a 93% enantiopure nitrone 2. Further studies concerning
these dramatic variations in the enantioselectivities as well as
improvements of the present method by the use of other organome-
tallics will be reported elswhere.
(22) Turner, M. J .; Luckenbach, L. A.; Turner, E. L. Synth. Commun.
1986, 16, 1377-1385.
(18) Rosantsev, E. G.; Sholle, V. D. Synthesis 1971, 401-414.

Additions and Corrections
J . Org. Chem., Vol. 62, No. 26, 1997 9387
mixture was then poured into a saturated NH4Cl solution (100
mL). The mixture was filtrated on a pad of Celite and extracted
with CH2Cl2 (3 × 100 mL). The combined organic phases were
dried over Na2SO4, and the solvent was removed under reduced
pressure. The crude product (5.35 g) was dissolved in methanol
(66 mL). To this solution were added concentrated ammonium
hydroxide (22 wt %, 5 mL) and copper(II) acetate monohydrate
(0.57 g, 2.85 mmol). Oxygen was bubbled through the yellow
solution so obtained until a persistent deep blue color was
observed. The solvent was then removed under reduced pres-
sure and the crude product redissolved in CHCl3 (100 mL). This
solution was washed with a saturated NaHCO3 solution (50 mL)
and dried over Na2SO4 and the solvent removed under reduced
pressure. The crude product (5.15 g) was dissolved in 50 mL of
anhydrous THF and treated with PhMgBr (same quantity and
conditions as above). After workup (see above) 6 g of crude
product was obtained. It was oxidized by O2/copper acetate
(same quantities, conditions, and workup as above), furnishing
7 g of brown viscous oil. Purification by column chromatography
on silica gel (hexane/EtOAc, 98:2) provided nitroxide 3 (1.17 g,
24% yield from 2, 93% ee), mp 123.5-129 °C. Two recrystalli-
zations from hexane gave 0.71 g of 3 with ee ) 99.8%: mp
(2S,5S)-2,5-Dim eth yl-2,5-d ip h en ylp yr r olid in e (4). A mix-
ture of 0.532 g (2 mmol) of nitroxide 3 (99.8% ee), 12 mL of water,
3 mL of concentrated hydrochloric acid, and 0.94 g (14 mmol) of
zinc powder were refluxed under vigorous stirring until the
yellow color of the nitroxide had disappeared (1 h). After cooling,
the reaction mixture was made alkaline (pH > 12) with
concentrated NaOH (30 wt %) and then extracted with Et2O.
The combined extracts were dried over Na2SO4; the solvent was
removed under reduced pressure to afford 0.502 g of pure 4 as
a colorless oil: bp 115 °C (0.5 mmHg). 4‚HCl: mp 165-168
°C; IR (neat) cm-1 3083, 3058, 3024, 2968, 1445, 1094, 1027; 1H
NMR δ (ppm) 1.34 (6H, s), 1.73 (1H, bs), 2.13-2.27 (4H, m),
7.19-7.62 (10H, m); 13C NMR δ (ppm) 32.3, 39.8, 65.4, 125.3,
125.9, 151.3. Anal. Calcd for C18H21N: C, 86.01; H, 8.41; N,
5.57. Found: C, 86.12; H, 8.50; N, 5.58.
Reoxid a tion of Am in e 4 in to Nitr oxid e 3. Amine 4 (25.1
mg, 0.1 mmol) was dissolved in a mixture of 1 mL of EtOH20
and 0.3 mL of water. To this solution were added, under
stirring, 106 mg (1 mmol) of Na2CO3 followed by 361 mg of Oxone
(0.46 mmol) in portions of ca. 50 mg every 10 min. At the end
of the addition, the mixture was stirred for another 5 h. The
solid was then filtered off and washed with ethanol. The
combined filtrate and washings were evaporated at reduced
pressure, and the residue was chromatographed on silica gel
(hexane/EtOAc, 98:2), affording 19.7 mg of nitroxide 3 (74%),
ee ) 99.8%.16
132.5-133 °C; [R]21 -170.5° (c 1.04, EtOAc); IR (KBr) 1601,
D
1496, 1444, 1416, 1372, 1269, 1063 cm-1; MS (DCI, NH3
+
isobutane) m/z 266 (100), 284 (16); UV-vis (0.32 10-3 M in
CH2Cl2) 241 nm (ꢀ ) 2500), 423 nm (ꢀ ) 4); ESR (1.3 10-3 M in
toluene) g ) 2.0066, aN ) 13.3 G. Anal. Calcd for C18H20NO:
C, 81.17; H, 7.56; N, 6.00. Found: C, 81.18; H, 7.72; N, 5.86.
J O971812P
Additions and Corrections
Vol. 60, 1995
Na r a sim h a ch a r i Na r a ya n a n , Lu cja n Str ek ow sk i,
Ma lgor za ta Lip ow sk a , a n d Ga bor P a ton a y*. A New Method
for the Synthesis of Heptamethine Cyanine Dyes: Synthesis of
New Near Infrared Fluorescent Labels.
Page 2391. L. Strekowski and M. Lipowska should be
included as authors for this paper.
Page 2395, Acknowledgment. This work was sup-
ported by a grant from LI-COR, Inc., Lincoln, NE.
J O974022O
Vol. 61, 1996
Leo P a qu ette* a n d J in gsu n g Ta e. Stereocontrolled Prepara-
tion of Spirocyclic Ethers by Intramolecular Trapping of Oxonium
Ions with Allylsilanes.
Scott E. Den m a r k * a n d Atli Th or a r en sen . Tandem [4 + 2]/
[3 + 2] Cycloadditions of Nitroalkenes. 10. trans-2-(1-Methyl-
1-Phenylethyl)cyclohexanol as a New Auxiliary.
Page 7860. The pioneering investigations by Denmark
on the stereochemistry and mechanism of allylmetal-
acetal additions were inadvertently not cited. The rel-
evant references are as follows.
Page 6728, Figure 2. Structure 8 in Figure 2 is
correctly depicted as the (1R) isomer for the intended
correlations. However, the (1R) isomer is dextrotatory
and the sign of rotation shown for 8 is in error, the correct
label is (+)-8.
(1) Denmark, S. E.; Willson, T. M. J . Am. Chem. Soc. 1989, 111, 3475.
(2) Denmark, S. E.; Willson, T. M. In Selectivities in Lewis Acid
Promoted Reactions; Schnizer, D., Ed.; Kluwer Academic Publishers:
1989; pp 247-263.
J O974005Z
J O974032P

9388
J . Org. Chem. 1997, 62, 9388
Vol. 62, 1997
Ra ym on d J . Cvetovich ,* Ch r is H. Sen a n a ya k e,
J osep h S. Am a to, Lisa M. DiMich ele, Tim oth y J .
Bill, J i Liu , Sh eo B. Sin gh , Rober t D. La r sen , R. F .
Sh u m a n , Th om a s R. Ver h oeven , a n d Ed w a r d J . J .
Gr a bow sk i. Practical Syntheses of 13-O-[(2-Methoxyethoxy)-
methyl]-22,23-dihydroavermectin B1 Aglycon [Dimedectin Iso-
propanol, MK-324] and 13-epi-O-(Methoxymethyl)-22,23-Dihy-
droavermectin B1 Aglycon [L-694,554], Flea Active Ivermectin
Analogues.
N. An d r e´ Sa sa k i,* Mich a el Dock n er , An ge`le Ch ia r on i,
Cla u d e Rich e, a n d P ier r e P otier . A Novel Stereodivergent
Synthesis of Optically Pure cis- and trans-3-Substituted Proline
Derivatives.
Page 766, column 1, lines 6-11, should read “While
5a exhibits a multiplet centered at 5.70 ppm which is
attributed to one of the allylic protons, its counterpart
of 5b appears somewhat downfield centered at 6.08 ppm
suggesting cis relationship between the allyl and the
hydroxymethyl groups.”
Page 3989. Due to an oversight, two names (J i Liu
and Sheo B. Singh) were not included in the list of
authors for this paper, for which they are fully deserving.
J O974017K
J O9740249
N. A. J . M. Som m er d ijk , P . J . J . A. Bu yn ster s, H.
Ak d em ir , D. G. Geu r ts, R. J . M. Nolte,* a n d Bin n e
Zw a n en bu r g*. Aziridines as Synthons for Chiral Amide-
Containing Surfactants.
Sh ik egi Ma tsu n a ga , Tosh iyu k i Wa k im oto, a n d Nobu h ir o
F u seta n i*. Isolation of Four New Calyculins from the Marine
Sponge Discodermia calyx.
Page 4958-9. The names of compounds 8b, 8c, 9b,
and 9c should read as follows: disodium (2S)-3-butanoyl-
2-(dodecanoylamino)propan-1-yl phosphate (8b), diso-
dium (2S)-3-butanoyl-2-(octadecanoylamino)propan-1-yl
phosphate (8c), disodium (2R)-3-butanoyl-1-(dodecanoyl-
amino)propan-2-yl phosphate (9b), and disodium (2R)-
3-butanoyl-1-(octadecanoylamino)propan-2-yl phosphate
(9c).
Page 2640. Structural formulas for compounds 1-5
were inadvertently drawn in an enantiomeric form.
J O9740251
Neville P . P a vr i a n d Ma r k L. Tr u d ell*. An Efficient Method
for the Synthesis of 3-Arylpyrroles.
Page 2649. The fourth sentence of the last paragraph
should read “A recent report describes the synthesis of
4a from benzonitrile in four steps and 37% overall
yield5...”.
J O974027L
Rober t B. Gr ossm a n * a n d Melissa A. Va r n er . Selective
Monoalkylation of Diethyl Malonate, Ethyl Cyanoacetate, and
Malononitrile Using a Masking Group for the Second Acidic
Hydrogen.
J O9740150
Den n is P . Ar n old * a n d Da vid A. J a m es. Dimers and Model
Monomers of Nickel(II) Octaethylporphyrin Substituted by
Conjugated Groups Comprising Combinations of Triple Bonds
with Double Bonds and Arenes. 1. Synthesis and Electronic
Spectra.
Page 5235. A relevant reference (Padgett, H. C.;
Csendes, I. G.; Rapoport, H. J . Org. Chem. 1979, 44,
3492) was inadvertently omitted. The reference describes
the use of triethyl methanetricarboxylate as a diethyl
malonate surrogate in the alkylation of 1,2-dibromoet-
hane and 1,4-dibromobutane. One ethoxycarbonyl group
could be removed from the alkylation product using
various acidic or basic conditions. Thanks to Prof.
Rapoport for bringing this work to our attention.
Page 3468, column 1. The electronic spectral data for
compound 25 were incorrect. The data should read as
follows: vis λmax 408 nm (ꢀ 153 000), 442 sh (100 000),
530 (24 400), 567 (30 000), 602 sh (21 000). The spectrum
displayed in Figure 6 is correct.
J O974026T
J O974023G
S0022-3263(97)04024-3 CCC: $14.00 © 1997 American Chemical Society