Allylation of exocyclic N-acyliminium ions generated from chiral N-[1-(phenylsulfonyl) alkyl] oxazolidin-2-ones

Article abstract of DOI:10.1021/jo0162888

N-[1-(Phenylsulfonyl)alkyl]oxazolidin-2-ones are successfully prepared by condensation of the corresponding optically active oxazolidin-2-ones with aldehydes and benzenesulfinic acid. At low temperature, in the presence of titanium tetrachloride, these sulfones are converted into N-acyliminium ions, which react with allyltrimethylsilane with a variable degree of stereoselectivity. The best results are obtained with (R)-5,5-dimethyl-4-phenyloxazolidin-2-one as a chiral auxiliary. Cleavage of the oxazolidin-2-one ring with lithium/ammonia affords the corresponding homoallylamines, which reveal an absolute configuration opposite that expected on the basis of the usual steric effects. A complexation of the Lewis acid with the N-acyliminium ion may be responsible of this rather unusual stereochemical outcome.

Full text of DOI:10.1021/jo0162888

J . Org. Chem. 2002, 67, 2989-2994
2989
Allyla tion of Exocyclic N-Acylim in iu m Ion s Gen er a ted fr om Ch ir a l
N-[1-(P h en ylsu lfon yl)a lk yl]oxa zolid in -2-on es†
Enrico Marcantoni, Tiziana Mecozzi, and Marino Petrini*
Dipartimento di Scienze Chimiche, Universita` di Camerino, via S. Agostino 1, I-62032 Camerino, Italy
marino.petrini@unicam.it
Received November 16, 2001
N-[1-(Phenylsulfonyl)alkyl]oxazolidin-2-ones are successfully prepared by condensation of the
corresponding optically active oxazolidin-2-ones with aldehydes and benzenesulfinic acid. At low
temperature, in the presence of titanium tetrachloride, these sulfones are converted into N-
acyliminium ions, which react with allyltrimethylsilane with a variable degree of stereoselectivity.
The best results are obtained with (R)-5,5-dimethyl-4-phenyloxazolidin-2-one as a chiral auxiliary.
Cleavage of the oxazolidin-2-one ring with lithium/ammonia affords the corresponding homoallyl-
amines, which reveal an absolute configuration opposite that expected on the basis of the usual
steric effects. A complexation of the Lewis acid with the N-acyliminium ion may be responsible of
this rather unusual stereochemical outcome.
Sch em e 1
In tr od u ction
Electrophilic substrates featuring carbon-nitrogen
double bonds as N-acyliminium ions have found a wide-
spread utilization as reactive intermediates for the
synthesis of functionalized amino derivatives.1 In com-
parison with the usual imino derivatives, these reagents
possess an enhanced reactivity that allows them to react
even with weak nucleophiles at low temperatures. N-
Acyliminium ion 2 is usually generated by an acid-
promoted elimination of R-substituted amido derivative
1 and is immediately made to react with a nucleophile
to the addition product 3 (Scheme 1).
The choice of a suitable leaving group X in the amido
derivative 1 is mandatory since it can affect the equilib-
rium in which the iminium ion is involved. R-Alkoxy
amides2 are the most popular precursors for N-acylimin-
ium ions even though the alkoxy group can sometimes
be substituted with other reactive leaving groups such
as halogens3 and amides.4 Particularly interesting is the
utilization of the phenylsulfonyl group for this purpose
since it acts as a good leaving group and its derivatives
are mostly stable solids easy to purify by crystallization.5
The chemistry of N-acyliminium ions has been mainly
addressed in regard to the synthesis of nitrogenated
heterocyclic compounds owing to their importance as
biologically active substances.6 This led to the develop-
ment of many stereoselective syntheses in which cyclic
N-acyliminium ions were involved.7 Much less attention
has been devoted to acyclic stereoselection produced by
optically active linear N-acyliminium ions8 or chiral
nucleophilic reagents with achiral N-acyliminium ions.9
In this paper we report the synthesis of optically active
(phenylsulfonyl)alkyloxazolidin-2-ones and their utiliza-
* To whom correspondence should be addressed. Phone: +39 0737
402253. Fax: +39 0737 637345.
(4) (a) Tohyama, Y.; Tanino, K.; Kuwajima, I. J . Org. Chem. 1994,
59, 518-519. (b) Ben-Ishai, D. J . Chem. Soc., Chem. Commun. 1980,
687-688.
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H. Eur. J . Org. Chem. 2000, 105-113. (b) Ostendorf, M.; Romagnoli,
R.; Cabeza Pereiro, I.; Roos, E. C.; Moolenaar, M. J .; Speckamp, W.
N.; Hiemstra, H. Tetrahedron: Asymmetry 1997, 8, 1773-1789. (c)
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(6) Review: (a) Hiemstra, H.; Speckamp, W. N. In The Alkaloids;
Brossi, A., Ed.; Academic Press: New York, 1988; Vol. 32, pp 271-
339. See also: (b) Kiewel, K.; Tallant, M.; Sulikowski, G. A. Tetrahe-
dron Lett. 2001, 42, 6621-6623. (c) Huang, H.-L.; Sung, W.-H.; Liu,
R.-S. J . Org. Chem. 2001, 66, 6193-6196. (d) Santos, L. S.; Pilli, R. A.
Tetrahedron Lett. 2001, 42, 6999-7001. (e) Pilli, R. A.; Zanotto, P. A.;
Bo¨ckelmann, M. A. Tetrahedron Lett. 2001, 42, 7003-7005. (f) Cole-
man, R. S.; Chen, W. Org. Lett. 2001, 3, 1141-1144. (g) Dhimane, H.;
Vanucci-Baque´, C.; Hamon, L.; Lhommet, G. Eur. J . Org. Chem. 1998,
1955-1963.
(7) For some very recent examples see: (a) Katritzky, A. R.; Metha,
S.; He, H.-Y. J . Org. Chem. 2001, 66, 148-152. (b) Batey, R. A.;
MacKay, D. B. Tetrahedron Lett. 2000, 41, 9935-9938. (c) D’Oca, M.
G. M.; Pilli, R. A.; Vencato, I. Tetrahedron Lett. 2000, 41, 9709-9712.
(d) Lennartz, M.; Steckhan, E.Tetrahedron 2001, 57, 675-680. (e)
Yamazaki, N.; Dokoshi, W.; Kibayashi, C. Org. Lett. 2001, 3, 193-
196.
† Dedicated to Professor Giuseppe Bartoli on the occasion of his 60th
birthday.
(1) Reviews: (a) Speckamp, W. N.; Moolenaar, M. J . Tetrahedron
2000, 56, 3817-3856. (b) De Koning, H.; Speckamp, W. N. In
Stereoselective Synthesis (Houben-Weyl); Helmchen, G., Hoffman, R.
W., Mulzer, J ., Schaumann, E.; Eds.; Georg Thieme Verlag: Stuttgart,
1995; Vol. E21, pp 1953-2009. (c) Hiemstra, H.; Speckamp, W. N. In
Comprehensive Organic Synthesis; Fleming, I., Trost, B. M., Heathcock,
C. H., Eds.; Pergamon: Oxford, 1991; Vol. 2, pp 1047-1082. (d)
Speckamp, W. N.; Hiemstra, H. Tetrahedron 1985, 41, 4367-4416.
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7, 2318-2323. (b) Suga, S.; Okajima, M.; Yoshida, J . Tetrahedron Lett.
2001, 42, 2173-2176. (c) Norton Matos, M. R. P.; Afonso, C. A. M.;
Batey, R. A. Tetrahedron Lett. 2001, 42, 7007-7010. (d) Tong, Y.;
Fobian, Y. M.; Wu, M.; Boyd, N. D.; Moeller, K. D. J . Org. Chem. 2000,
65, 2484-2493. (e) Okitsu, O.; Suzuki, R.; Kobayashi, S. J . Org. Chem.
2001, 66, 809-823. (f) Schuch, C. M.; Pilli, R. A. Tetrahedron:
Asymmetry 2000, 11, 753-764. (g) Russowsky, D.; Petersen, R. Z.;
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4748.
10.1021/jo0162888 CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/11/2002

2990 J . Org. Chem., Vol. 67, No. 9, 2002
Marcantoni et al.
Sch em e 2
Sch em e 3
Ta ble 1. Syn th esis of P h en ylsu lfon yloxa zolid in -2-on es 9
yield,b
%
entry
7
aldehyde 8
EtCHO (8a )
(CH3)2CHCH2CHO (8b)
(CH3)2CHCHO (8c)
PhCH2CH2CHO (8d )
n-C7H15CHO (8e)
9
dra
1
2
3
4
5
6
7
8
9
10
11
12
13
7a
7a
7a
7a
7a
7a
7a
7b
7b
7b
7b
7c
7d
9a
9b
9c
9d
9e
9f
85:15
85:15
80:20
90:10
90:10
90:10
90:10
80:20
90:10
75:25
75:25
80:20
80:20
95
86
70
68
80
72
78
75
65
83
95
68
83
tion as precursors of N-acyliminium ions in the reaction
with allyltrimethylsilane.
Resu lts a n d Discu ssion
Cl(CH2)5CHO (8f)
CH2dCH(CH2)7CHO (8g) 9g
Syn th esis of N-[1-(P h en ylsu lfon yl)a lk yl]oxa zoli-
d in -2-on es. Recently, we have reported that chiral
exocyclic N-acyliminium ions 5 can be generated starting
from N-[1-(phenylsulfonyl)alkyl] imidazolidin-2-ones 410
in the presence of tin tetrachloride.11 These electrophilic
ions have been made to react with different nucleophiles,
giving the corresponding addition products 6 in good
yields and high diastereoselectivities (Scheme 2). Unfor-
tunately, the imidazolidin-2-one ring has proved to be
resistant to various cleavage conditions, and therefore,
the preparation of primary amino derivatives is not
achievable by this method. Thus, we turned our attention
to the use of oxazolidin-2-ones as chiral auxiliaries12 since
they are readily available compounds and are cleavable
under reductive conditions.13
Classical methods used for the synthesis of phenyl-
sulfonyl derivatives of imidazolidin-2-ones and cogeners
usually involve a reaction with an aldehyde and sodium
benzenesulfinate in aqueous solutions.10,11 However,
these conditions are totally uneffective when 4-substi-
tuted oxazolidin-2-ones are used as substrates probably
because of the unfavorable equilibrium that hinders the
formation of the phenylsulfonyl derivative in water.14 For
this reason we decided to exploit the formation of
(phenylsulfonyl)alkyloxazolidin-2-ones in organic solvents
using benzenesulfinic acid in place of its sodium salt.
Oxazolidin-2-ones 7 react with aldehydes 8 and benzene-
sulfinic acid in dry dichloromethane and in the presence
of magnesium sulfate, which acts as a water scavenger,
8b
8c
8d
8e
8b
8b
9h
9i
9j
9k
9l
9m
The diastereomeric ratio was evaluated by 1H NMR analysis
a
b
Yields of pure, isolated products.
giving (phenylsulfonyl)alkyloxazolidin-2-ones 9 in good
yield (Scheme 3, Table 1). However, unlike (phenylsul-
fonyl)alkylimidazolidin-2-ones 4, which are formed as
single diastereomers, compounds 9 are produced as
epimeric mixtures with variable stereoselectivity. The
utilization of trisubstituted oxazolidin-2-ones 7b,c, which
have been recently introduced as chiral auxiliaries,4b,d
does not seem to offer any beneficial effect on the
stereoselectivity of sulfonyl derivatives 9h -k . Pure
samples of the major diastereomer can be obtained for
analytical purposes by repeated crystallizations in ethyl
acetate. The stereochemistry of the newly formed stereo-
center in sulfones 9 is S in the major stereoisomer as
confirmed by the X-ray crystallographic analysis carried
out for compound 9h .
Allyla tion of Ch ir a l (P h en ylsu lfon yl)a lk yloxa zo-
lid in -2-on es 9. The formation of N-acyliminium ions
from their precursors strongly depends on the nature of
the Lewis acid used. Tin tetrachloride works very ef-
ficiently with derivatives 4 and unsubstituted (phenyl-
sulfonyl)alkyloxazolidin-2-ones 9 (Scheme 3; R ) R1
)
H; R2 ) Et) since a slight excess (1.25 equiv) of this Lewis
acid is usually required to afford the corresponding
addition products 6 in good yield.11 However, substituted
(phenylsulfonyl)alkyloxazolidin-2-ones 9 necessitate a
large excess (5 equiv) of tin tetrachloride to be converted
into the allyl derivatives 11. The yields of allylated
products 11 obtained are quite modest, and furthermore,
the elevated amounts of tin salts employed make the
(8) (a) Mu¨ller, R.; Ro¨ttele, H.; Henke, H,; Waldmann, H. Chem. Eur.
J . 2000, 6, 2032-2043. (b) Rae, A.; Castro, J . L.; Tabor, A. B. J . Chem.
Soc., Perkin Trans. 1 1999, 1943-1948. (c) Hioki, H.; Okuda, M.;
Miyiagi, W.; Itoˆ, S. Tetrahedron Lett. 1993, 34, 6131-6134. (d) Seebach,
D.; Charczuk, R.; Gerber, C.; Renaud, P.; Berner, H.; Schneider, H.
Helv. Chim. Acta 1989, 72, 401-425. (e) Harding, K. E.; Davis, C. S.
Tetrahedron Lett. 1988, 29, 1891-1894.
(9) (a) Marshall, J . A.; Gill, K.; Seletsky, B. M. Angew. Chem., Int.
Ed. 2000, 39, 953-956. (b) Panek, J . S.; J ain, N. F. J . Org. Chem.
1994, 59, 2674-2675.
(10) Pearson, W. H.; Lindbeck, A. C.; Kampf, J . W. J . Am. Chem.
Soc. 1993, 115, 2622-2636.
(11) Giardina`, A.; Mecozzi, T.; Petrini, M. J . Org. Chem. 2000, 65,
8277-8282.
(12) (a) Ager, D. J .; Prakash, I.; Schaad, D. R. Chem. Rev. 1996, 96,
835-875. (b) Hintermann, T.; Seebach, D. Helv. Chim. Acta 1998, 81,
2093-2126. (c) Wu, Y.; Shen, X. Tetrahedron: Asymmetry 2000, 11,
4359-4363. (d) Bull, S. D.; Davies, S. G.; J ones, S.; Sanganee, H. J . J .
Chem. Soc., Perkin Trans. 1 1999, 387-398.
(13) (a) Lucet, D.; Sabelle, S.; Kosterlitz, O.; Le Gall, T.; Mioskowski,
C. Eur. J . Org. Chem. 1999, 2583-2591. (b) Boger, D. L.; Myers, J . B.
J . Org. Chem. 1991, 56, 5385-5390. (c) Evans, D. A.; Sjogren, E. B.
Tetrahedron Lett. 1985, 26, 3783-3786.
(14) Oxazolidin-2-one can be efficiently transformed into the corre-
sponding phenylsulfonyl derivative in aqueous solution; see refs 10
and 11. Other methods for the synthesis of R-amidoalkylphenyl
sulfones: (a) Schunk, S.; Enders, D. Org. Lett. 2001, 3, 3177-3180.
(b) Nagano, T.; Kinoshita, H. Bull. Chem. Soc. J pn. 2000, 73, 1605-
1613. (c) Chemla, F.; Hebbe, V.; Normant, J .-F. Synthesis 2000, 75-
77. (d) Sisko, J .; Mellinger, M.; Sheldrake, P. W.; Baine, N. H.
Tetrahedron Lett. 1996, 37, 8113-8116. (e) Morton, J .; Rahim, A.;
Walker, E. R. H. Tetrahedron Lett. 1982, 23, 4123-4126. (f) Weygand,
F.; Steglich, W. Chem. Ber. 1965, 98, 487-503. (g) Engberts, J . B. F.
N.; Strating, J . Recl. Trav. Chim. Pays-Bas 1965, 84, 942-950.

Allylation of Exocyclic N-Acyliminium Ions
J . Org. Chem., Vol. 67, No. 9, 2002 2991
Ta ble 2. Syn th esis of Allyloxa zolid in -2-on es 11
Sch em e 5
allyl
derivative 11
yield,b
%
entry
sulfone 9
dra
1
2
9a
9b
11a
11b
70:30
65:35
70:30c
55:45
80:20
75:25
60:40
70:30
90:10
90:10c
95:5
73
78
46c
85
66
70
91
80
93
55c
73
78
79
58
68
3
4
5
6
7
8
9c
9d
9e
9f
9g
9h
11c
11d
11e
11f
11g
11h
Ta ble 3. Syn th esis of Ca r ba m a tes 13 by Red u ctive
Clea va ge of Allyloxa zolid in -2-on es 11
9
10
11
12
13
9i
9j
9k
9l
9m
11i
11j
11k
11l
11m
allyl
derivative 11
carbamate
12-19
yield,b
%
85:15
90:10
65:35
75:25
entry
era
1
2
3
4
5
6
7
8
9
11a
11b
11c
11d
11e
11f
11g
11h
11i
11j
11k
11l
12
13
14
15
16
17
18
19
14
15
16
19
75:25
70:30
58:42
78:22
70:30
c
74:26
92:8
94:6
78
72
80
71
75
51
76
82
88
77
75
70
a
1
The diastereomeric ratio was evaluated by H NMR analysis.
Yields of pure, isolated products. c Values obtained using 5 equiv
b
of tin tetrachloride as activator.
Sch em e 4
10
11
12
88:12
90:10
68:22
a
The enantiomeric ratio was evaluated by GLC analysis on a
b
chiral column (see the Experimental Section). Yields of pure,
isolated products. c Not evaluated.
4,5,5-triphenyloxazolidin-2-one (7c) and (4S)-4-isopropyl-
oxazolidin-2-one (7d ) (Table 2, entries 12 and 13) did not
introduce any improvement compared to that of 5,5-
dimethyl derivative 7b. The assignment of the absolute
configuration of the newly formed stereocenter in com-
pounds 11 was rather troublesome since any attempt to
obtain crystals suitable for an X-ray analysis from these
allyl derivatives failed.15
Therefore, we sought a chemical correlation that could
enable us to elucidate the stereochemistry of compounds
11. Cleavage of the 4-phenyloxazolidin-2-one ring in
compounds 11a -l has been efficiently carried out under
reductive conditions using Li/NH3 in a mixture of THF/
t-BuOH at -78 °C.13a (Scheme 5).
The resulting crude homoallylamines obtained after
evaporation of the solvents have been converted into the
corresponding carbamates 12-19 (Table 3). Cleavage of
4-phenyloxazolidin-2-ones using metals in liquid am-
monia usually occurs with complete retention of the
configuration at the stereocenter adjacent to the nitrogen
atom.13 This behavior has been confirmed by evaluating
the enantiomeric ratio of carbamates 12-19 by GLC
analysis using a chiral capillary column (Table 3). A
comparison between the sign of the optical rotation of
these N-protected homoallylamines with that available
in the literature for the same compound demonstrated
that the absolute configuration of carbamate 19 obtained
from 11h is S16 and that of carbamate 14 obtained from
11i is R.17 The stereochemistry of other carbamates, 12,
13, and 15-18, has been inferred by analogy with 14 and
19 considering that the same mechanism operates for the
allylation process. Surprisingly, this result is the opposite
usual workup procedures rather troublesome (Table 2,
entries 2 and 8). Conversely, titanium tetrachloride (2
equiv) is able to turn sulfones 9 into the corresponding
N-acyliminium ions in dichloromethane at -78 °C, which,
upon reaction with allyltrimethylsilane 10, give the
addition products 11 in good yields (Scheme 4, Table 2).
Other Lewis acids tested as BF3‚Et2O or AlCl3 gave
only poor yields of allylated products 11 as previously
observed with compounds 4.11 Unsatisfactory results have
been obtained using allyltributylstannane as allylating
reagent with various Lewis acids at different tempera-
tures. Sulfones 9a -g obtained from (R)-4-phenyloxazo-
lidin-2-one (7a ) (Table 2, entries 1-7) afford the corre-
sponding allyl derivatives 11a -g only with modest
diastereoselectivity. It is interesting to note that the
diasteromeric ratio of allylated products 11 is not affected
by the diastereomeric composition of sulfones 9. Indeed,
pure (4R,1′S)-9e gives the allylated product 11e (Table
2, entry 5) in a 75:25 diastereomeric ratio, a value similar
to that obtained using variable diastereomeric mixtures
of 9e. This result clearly indicates that the stereochemical
outcome of our reaction is governed only by the diaster-
eomeric composition of N-acyliminium ion formed as well
as the diastereofacial preference of the subsequent nu-
cleophilic addition. Sulfones 9h -k obtained from (R)-5,5-
dimethyl-4-phenyloxazolidin-2-one (7b) (Table 1, entries
8-11) have been converted into the corresponding allyl
derivatives 11h -k using the usual procedure in good
yields (Table 2, entries 8-11). The diastereoselectivity
of allyl derivatives 11h -k obtained is higher than that
previously observed using unsubstituted oxazolidin-2-one
7a . The utilization of other chiral auxiliaries such as (4R)-
(15) Compounds 11 are mostly oils or low melting point solids.
Derivative 11m is actually a solid (mp 213 °C), but it does not give
crystals in any of the solvents tested.
(16) Enders, D.; Schankat, J .; Klatt, M. Synlett 1994, 795-797.
(17) Hunt, J . C. A.; Lloyd, C.; Moody, C. J .; Slawin, A. M. Z.; Takle,
A. K. J . Chem. Soc., Perkin Trans. 1 1999, 3443-3454.

2992 J . Org. Chem., Vol. 67, No. 9, 2002
Marcantoni et al.
Sch em e 6
from 7b. Indeed, to relieve the eclipsing interation
between the phenyl and the cis-methyl in 7b, the
heterocycle should constrain the trans-methyl to assume
an axial position that cooperates to facilitate the attack
of allyltrimethylsilane on the same side of the aromatic
ring. An alternative explanation of this unusual stereo-
chemical outcome could be found in a higher reactivity
of the (Z)-N-acyliminium ion (e.g., 20, Scheme 6), which
reacts faster than the E stereoisomer, thus shifting the
equilibrium toward the formation of the observed major
diastereomer 1′S-11. The lack of reactivity displayed by
other nucleophilic reagents such as silyl enol ethers may
be ascribed to the low rate by which the N-acyliminium
ion is formed from 9, which favors a decomposition of the
silyl enol ether by the excess of the Lewis acid used.20
In summary, condensation of optically active oxazoli-
din-2-ones 7 with an aldehyde in the presence of benze-
nesulfinic acid leads to the synthesis of (phenylsulfonyl)-
alkyloxazolidin-2-ones 9 in good yield. These sulfonyl
derivatives react with titanium tetrachloride at low
temperature, giving the corresponding N-acyliminium
ions, which are allylated using allyltrimethylsilane. The
diastereomeric ratio of allyl derivatives 11 is quite modest
using oxazolidin-2-one 7a as chiral auxiliary, while
satisfactory results are obtained using 7b. The diastereo-
facial preference experienced in the formation of allyl
derivatives 11 is opposite that observed in similar ad-
ducts observed from sulfones 4. Cleavage of the oxazoli-
din-2-one ring of allyl derivatives 11 affords the corre-
sponding optically active homoallylamines, which have
been isolated as the corresponding carbamates 12-19.
of what is expected on the basis of the structural features
of the N-acyliminium ions involved in the process.
Assuming as the most probable an attack from the upper
face of the N-acyliminium ion intermediate, the prevail-
ing diastereomer (1′S)-11 would be formed by reaction
of (Z)-20 and (Z)-21 with allyltrimethylsilane (Scheme
6).
However, the Z stereoisomer of these reactive ions
seems to be less stable than the E one probably because
of the 1,3-allylic strain between the alkyl chain and the
carbonyl oxygen.10,11 This assumption is also supported
by semiempirical calculations (PM3)18 made on interme-
diates 20 and 21, which show for the Z stereoisomers
energy levels 0.7 and 1.4 kcal/mol higher than those of
the E stereoisomers. On the other hand, since an N-
acyliminium ion is also involved in the formation of
sulfones 9, the stereochemistry of the additional stereo-
center in these compounds confirms the preference for
the E configuration of this reactive intermediate even at
room temperature. It is interesting to note that the
utilization of tin tetrachloride as activator leads to the
synthesis of allyl derivatives 11b,h with almost the same
diastereomeric ratio and, most importantly, with the
same diastereofacial preference observed with titanium
tetrachloride. The nature of the actual interaction exist-
ing between the N-acyliminium ion and the Lewis acid
is unknown, but it is evident that even the introduction
of small structural modifications in the core structure of
the heterocyclic ring of the chiral auxiliary leads to a
consistent change in the conformation of the reactive
intermediate. In particular, titanium shows a marked
coordinating ability and, especially when it is used in low
ionizating solvents as dichloromethane, could give rise
to tight ionic pair couples with the carbonyl group of the
oxazolidin-2-one.19 In this couple, the metal and its
ligands may force the alkyl chain to occupy the upper
side face of the N-acyliminium ion (si-si), thus fostering
the nucleophilic attack from the opposite face (re-re). This
hypothesis would also explain the improved diastereo-
selectivity experienced using sulfones 9h -k obtained
Exp er im en ta l Section
1H NMR was performed at 300 MHz in CDCl3 as solvent.13C
NMR was performed at 75 MHz in CDCl3 as solvent. The
enantiomeric ratio of carbamates 12-19 was evaluated by
GLC using a chiral column (30:70 dimethylpentylbetacyclo-
dextrin-OV1701, 0.25 µm × 0.25 mm i.d., length 25 m, ∆T )
50-180 °C at 2 °C/min). Dichloromethane was dried by
refluxing it over calcium hydride and then distilled. All
chemicals used are available commercially. Oxazolidin-2-ones
7b-d were prepared using a literature method.12d
P r ep a r a tion of Ben zen esu lfin ic Acid fr om Its Sod iu m
Sa lt. Sodium benzenesulfinate (1.64 g, 10 mmol) was dissolved
in water (5 mL), and then 6 N H2SO4 was added until the pH
reached 1. The white suspension was extracted with CHCl3
and dried over MgSO4. Removal of the solvent at reduced
pressure afforded 1.35 g of benzenesulfinic acid (95%).
Gen er a l P r oced u r e for th e P r ep a r a tion of P h en ylsu l-
fon yl Der iva tives 9. Oxazolidin-2-one 7 (5 mmol) was dis-
solved in dichloromethane (15 mL), and then benzenesulfinic
acid (10 mmol), the appropriate aldehyde (7.5 mmol), and
anhydrous MgSO4 (0.5 g) were sequentially added at room
temperature. The mixture was stirred for 36 h at room
temperature and then filtered over a short pad of Florisil.
Removal of the solvent afforded the crude sulfone 9, which
was purified by crystallization (4:1 hexanes-ethyl acetate) or
column chromatography (7:3 hexanes-ethyl acetate).
Da ta for (4R)-3-[1-(P h en ylsu lfon yl)p r op yl]-4-p h en yl-
oxa zolid in -2-on e (9a ): mixture of 1′S and 1′R (85:15) dia-
stereomers; yield 95%; oil; [R]20D ) -90 (c 1.6, CHCl3); IR (cm-1
,
(18) Semiempirical PM3 calculations were performed with Spartan
5.0.3, Wavefunction Inc., 18401 Von Karmen Ave., no. 370, Irvine, CA
92715.
(19) According to the observations of Denmark and Almstead, a 1:1
complex between TiCl4 and aldehydes is formed in dichloromethane.
Furthermore, the formation of allyltrichlorotitanium species, which
could lead to an intramolecular delivery of the allyl group, can be
definitely ruled out. Denmark, S. E.; Almstead, N. G. Tetrahedron
1992, 48, 5565-5578.
(20) We thank a reviewer for this useful suggestion. It is known
that increasing the electron-withdrawing aptitude of the acyl group
usually leads to a decrease in the N-acyliminium ion stability.
Therefore, imidazolidinones would be more efficient than oxazolidi-
nones in promoting the formation of N-acyliminium ions (see ref 1b).
Preliminary results also indicate that electron-rich aromatic derivatives
are able to react with sulfones 9, giving the corresponding addition
products.

Allylation of Exocyclic N-Acyliminium Ions
J . Org. Chem., Vol. 67, No. 9, 2002 2993
neat) 1695, 1375, 1145; 1H NMR (1′S) δ (ppm) 0.53 (t, 3H, J )
7.3 Hz), 1.28-1.44 (m, 1H), 1.75-1.91 (m, 1H), 4.18 (dd, 1H,
J ) 9.3, 4.4 Hz), 4.49 (t, 1H, J ) 8.9 Hz), 4.97 (dd, 1H, J )
1.7, 4.0 Hz), 5.34 (dd, 1H, J ) 8.9, 4.3 Hz), 7.30-7.43 (m, 5H),
1H), 6.86-7.22 (m, 8H), 7.34-7.55 (m, 6H), 7.66-7.72 (m, 4H),
7.83-7.87 (m, 2H). Anal. Calcd for C32H31NO4S (525.66): C,
73.12; H, 5.94; N, 2.66. Found: C, 73.07; H, 5.99; N, 2.70.
Da ta for (4R,1′S)-3-[1-(P h en ylsu lfon yl)-3-m eth ylbu tyl]-
4-isop r op yloxa zolid in -2-on e (9m ): purified by a preliminary
column chromatography and successively by crystallization;
7.52-7.59 (m, 2H), 7.63-7.67(m, 1H), 7.91-7.97 (m, 2H); 13
C
NMR δ (ppm) 10.3, 18.6, 57.2, 71.2, 76.8, 127.4, 128.6, 129.2,
129.3, 129.4, 129.5, 134.5, 137.1, 139.5, 158.3. Anal. Calcd for
yield 83%; mp 87 °C; [R]20 ) -21 (c 1.0, CHCl3); IR (cm-1
,
D
1
C
18H19NO4S (345.41): C, 62.59; H, 5.54; N, 4.06. Found: C,
KBr) 1690, 1377, 1133; H NMR δ (ppm) 0.87 (d, 3H, J ) 6.4
Hz), 0.88 (d, 3H, J ) 6.7 Hz), 0.92 (d, 3H, J ) 6.4 Hz), 0.93 (d,
3H, J ) 6.7 Hz), 1.63-2.08 (m, 3H), 4.03 (d, 1H, J ) 8.9 Hz),
4.13 (dd, J ) 8.9, 2.7 Hz), 4.18-4.30 (m, 1H), 5.18-5.24 (m,
1H), 7.53-7.60 (m, 2H), 7.63-7.61 (m, 1H), 7.87-7.95 (m, 2H).
Anal. Calcd for C17H25NO4S (339.45): C, 60.15; H, 7.42; N,
4.13. Found: C, 60.11; H, 7.37; N, 4.14.
62.65; H, 5.51; N, 3.99.
Da ta for (4R,1′S)-3-[1-(P h en ylsu lfon yl)-3-m eth ylbu tyl]-
4-p h en yloxa zolid in -2-on e (9b): purified by crystallization;
yield 86%; mp 121 °C; [R]20 ) -44 (c 1.5, CHCl3); IR (cm-1
,
D
1
KBr) 1690, 1377, 1133; H NMR δ (ppm) 0.22 (d, 3H, J ) 6.4
Hz), 0.67 (d, 3H, J ) 6.4 Hz), 1.02-1.14 (m, 1H), 1.38-1.46
(m, 2H), 4.21 (dd, 1H, J ) 8.9, 4.3 Hz), 4.48 (t, 1H, J ) 8.9
Hz), 5.12-5.19 (m, 1H), 5.36 (dd, J ) 8.9, 4.3), 7.32-7.43 (m,
5H), 7.55-7.61 (m, 2H), 7.65-7.69 (m, 1H), 7.92-7.97 (m, 2H);
13C NMR δ (ppm) 20.6, 22.4, 24.6, 32.8, 57.0, 71.2, 73.6, 127.4,
128.6, 129.3, 129.5, 134.5, 137.1, 139.5, 158.3. Anal. Calcd for
Gen er a l P r oced u r e for th e P r ep a r a tion of Allyloxa zo-
lid in -2-on es 11. Sulfone 9 (2 mmol) was dissolved in CH2Cl2
(20 mL), and the solution was cooled to -78 °C. TiCl4 (4 mmol)
was then added dropwise in 15 min, and the temperature was
kept at -78 °C for 30 min. Allyltrimethylsilane (4 mmol)
dissolved in CH2Cl2 (10 mL) was then added dropwise, and
after 1 h at -78 °C the temperature was slowly raised to 0
°C. The reaction mixture was then diluted with CH2Cl2 (20
mL) and washed with brine (10 mL), and the organic phase
was dried over MgSO4. After removal of the solvent at reduced
pressure, the allylation product 11 obtained was purified by
column chromatography (7:3 hexanes-ethyl acetate).
C
20H23NO4S (373.46): C, 64.32; H, 6.21; N, 3.75. Found: C,
64.28; H, 6.24; N, 3.77.
Da ta for (4R)-3-[1-(P h en ylsu lfon yl)-2-m eth ylp r op yl]-
4-p h en yloxa zolid in -2-on e (9c): mixture of 1′S and 1′R (80:
20) diastereomers; yield 70%; oil; [R]20 ) -80 (c 1.2, CHCl3);
D
IR (cm-1, neat) 1692, 1373, 1136; 1H NMR δ (ppm) 0.57 (d,
3H, J ) 6.6 Hz), 0.98 (d, 3H, J ) 6.6 Hz), 1.89-2.08 (m, 1H),
4.26 (dd, 1H, J ) 8.7, 4.3 Hz), 4.37 (t, 1H, J ) 8.8 Hz), 4.97 (d,
1H, J ) 10.7 Hz), 5.25 (dd, 1H, J ) 8.8, 4.3 Hz), 7.35-7.50
(m, 5H), 7.54-7.72 (m, 3H), 7.95-8.01 (m, 2H); 13C NMR δ
(ppm) 20.0, 20.8, 27.8, 57.8, 71.5, 81.8, 127.9, 128.1, 129.3,
Da ta for (4R)-3-(1-Eth ylbu t-3-en yl)-4-p h en yloxa zoli-
d in -2-on e (11a ): mixture of 1′S and 1′R (70:30) diastereo-
mers; yield 73%; oil [R]20 ) -26.1 (c 2.3, CHCl3); IR (cm-1
,
D
1
neat) 1692; H NMR (1′S) δ (ppm) 0.80 (t, 3H, J ) 7.3 Hz),
1.55-1.76 (m, 2H), 1.81-1.90 (m, 1H), 2.09-2.18 (m, 1H),
3.32-3.41 (m, 1H), 4.13 (dd, 1H, J ) 8.5, 6.7 Hz), 4.55 (t, 1H,
J ) 9.0 Hz), 4.71 (dd, 1H, J ) 8.9, 6.4 Hz), 4.86-5.02 (m, 2H),
5.60-5.72 (m, 1H), 7.31-7.42 (m, 5H); 13C NMR δ (ppm) 11.3,
24.5, 37.6, 56.7, 59.8, 70.1, 117.5, 127.7, 129.0, 129.1, 135.3,
139.2, 158.2. Anal. Calcd for C15H19NO2 (245.32): C, 73.44;
H, 7.81; N, 5.71. Found: C, 73.50; H, 7.86; N, 5.68.
129.4, 129.5, 134.3, 139.1, 139.5, 159.0. Anal. Calcd for C19H21
-
NO4S (359.44): C, 63.49; H, 5.89; N, 3.90. Found: C, 63.55;
H, 5.91; N, 3.86.
Da ta for (4R,1′S)-5,5-Dim eth yl-3-[1-(p h en ylsu lfon yl)-
3-m eth ylbu tyl]-4-p h en yloxa zolid in -2-on e (9h ): purified by
crystallization; yield 75%; mp 122 °C; [R]20 ) -26.3 (c 2.9,
D
CHCl3); IR (cm-1, KBr) 1690, 1377, 1133; 1H NMR δ (ppm)
0.19 (d, 3H, J ) 6.1 Hz), 0.55 (d, 3H, J ) 6.1 Hz), 1.01 (s, 3H),
1.12-1.41 (m, 3H), 1.65 (s, 3H), 4.97 (s, 1H), 5.23 (d, 1H, 10.6
Hz), 7.25-7.44 (m, 5H), 7.53-7.70 (m, 3H), 7.93-7.99 (m, 2H);
13C NMR δ (ppm) 21.1, 22.7 24.1, 24.6, 28.6, 34.7, 66.5, 73.5,
83.8, 126.9, 128.8, 129.3, 129.7, 130.1, 134.4, 135.0, 137.9,
158.5. Anal. Calcd for C22H27NO4S (401.52): C, 65.81; H, 6.78;
N, 3.49. Found: C, 65.87; H, 6.84; N, 3.53.
Da ta for (4R)-3-(1-P h en eth ylbu t-3-en yl)-4-p h en yloxa -
zolid in -2-on e (11d ): mixture of 1′S and 1′R (80:20) diaster-
eomers; yield 66%; mp 72 °C; [R]20D ) -18.7 (c 2.5, CHCl3); IR
1
(cm-1, KBr) 1690; H NMR (1′S) δ (ppm) 1.86-2.84 (m, 4H),
2.38-2.61 (m, 2H), 3.43-3.48 (m, 1H), 4.17 (dd, 1H, J ) 8.6,
6.6 Hz), 4.49 (t, 1H, J ) 8.8 Hz), 4.70 (dd, 1H, J ) 8.9, 6.6
Hz), 4.91-5.08 (m, 2H), 5.55-5.83 (m, 1H), 7.31-7.43 (m,
10H); 13C NMR δ (ppm) 33.1, 37.5, 54.9, 60.2, 70.0, 117.8,
125.9, 127.7, 128.2, 128.4, 129.1, 129.2, 135.0, 139.1, 141.2,
158.0. Anal. Calcd for C21H23NO2 (321.41): C, 78.47; H, 7.21;
N, 4.36. Found: C, 78.50; H, 7.24; N, 4.37.
Da ta for (4R,1′S)-5,5-Dim eth yl-3-[1-(p h en ylsu lfon yl)-
3-p h en ylp r op yl]-4-p h en yloxa zolid in -2-on e (9j): purified by
repeated cystallizations; yield 83%; mp 96 °C; [R]20D ) +7.2 (c
2.1, CHCl3); IR (cm-1, KBr) 1691, 1378, 1135; 1H NMR δ (ppm)
1.01 (s, 3H), 1.68 (s, 3H), 1.73-1.84 (m, 1H), 2.12-2.40 (m,
2H), 2.72-2.84 (m, 1H), 5.03 (s, 1H), 5.19 (dd, 1H, J ) 9.5,
3.7 Hz), 6.48-6.53 (m, 2H), 6.97-7.06 (m, 3H), 7.11-7.27 (m,
2H), 7.32-7.43 (m, 3H), 7.45-7.64 (m, 3H), 7.80-7.89 (m, 2H);
13C NMR δ (ppm) 24.2, 27.6, 29.0, 31.9, 66.9, 73.9, 83.5, 126.2,
126.4, 128.0, 128.3, 128.6, 128.8, 129.2, 129.5, 129.7, 134.3,
137.2, 139.1, 158.1. Anal. Calcd for C26H27NO4S (449.56): C,
69.46; H, 6.05; N, 3.12. Found: C, 69.44; H, 6.01; N, 3.15.
Da ta for (4R,1′S)-5,5-Dim eth yl-3-(1-isobu tylbu t-3-en yl)-
4-p h en yloxa zolid in -2-on e (11h ): yield 93%; oil; [R]20
)
D
-23.4 (c 2.2, CHCl3); IR (cm-1, neat) 1695; H NMR δ (ppm)
0.81 (d, 3H J ) 6.4 Hz), 0.85 (d, 3H, J ) 6.3 Hz), 0.94 (s, 3H),
1.48-1.63 (m, 3H), 1.50 (s, 3H), 1.74-1.90 (m, 1H), 2.26-2.45
(m, 1H), 3.47-3.62 (m, 1H), 4.34 (s, 1H), 4.93-5.05 (m, 2H),
5.61-5.78 (m, 1H), 7.32-7.40 (m, 5H); 13C NMR δ (ppm) 22.7,
23.2, 24.5, 25.6, 29.6, 38.4, 41.5, 53.4, 70.0, 81.4, 118.1, 128.6,
129.0, 129.3, 136.0, 137.6, 157.8 Anal. Calcd for C19H27NO2
(301.42): C, 75.71; H, 9.03; N, 4.65. Found: C, 75.74; H, 9.00;
N, 4.63.
1
Da ta for (4R)-5,5-Dim eth yl-3-[1-(p h en ylsu lfon yl)octyl]-
4-p h en yloxa zolid in -2-on e (9k ): mixture of 1′S and 1′R (75:
25) diastereomers; yield 95%; oil; [R]20 ) -19.3 (c 2, CHCl3);
D
Da t a for (4R,1′S)-5,5-Dim et h yl-3-(1-p h en et h ylb u t -3-
IR (cm-1, neat) 1688, 1375, 1134; 1H NMR δ (ppm) 0.77 (t 3H,
J ) 7.2 Hz), 0.92-1.03 (m, 2H), 0.97 (s, 3H), 1.05-1.36 (m,
8H), 1.52-1.59 (m, 2H), 1.60 (s, 3H), 4.94 (s, 1H), 5.13 (dd,
1H, J ) 10.8, 2.9 Hz), 7.32-7.39 (m, 5H), 7.537.67 (m, 3H),
7.86-7.95 (m, 2H); 13C NMR δ (ppm) 14.0, 22.4, 24.1, 25.7,
26.0, 27.0, 28.5, 28.9, 31.5, 66.9, 74.7, 83.2, 128.7, 128.9, 129.2,
en yl)-4-p h en yloxa zolid in -2-on e (11j): yield 78%; oil; [R]20
D
) -20.7 (c 2.0, CHCl3); IR (cm-1, KBr) 1691; 1H NMR δ (ppm)
0.97 (s, 3H), 1.57 (s, 3H), 1.94-2.13 (m, 4H), 2.37-2.51 (m,
2H), 2.54-2.68 (m, 2H), 3.38-3.51 (m, 1H), 4.40 (s, 1H), 4.95-
5.06 (m, 2H), 5.62-5.68 (m, 1H), 6.97-7.40 (m, 10H); 13C NMR
δ (ppm) 23.7, 28.9, 32.9, 33.1, 33.4, 37.1, 54.4, 68.3, 69.8,
81.0, 117.7, 125.7, 127.9, 128.0, 128.1, 128.2, 128.4, 128.7,
128.8, 135.0, 136.4, 140.9, 157.1. Anal. Calcd for C23H27NO2
(349.47): C, 79.05; H, 7.79; N, 4.01. Found: C, 79.10; H, 7.83;
N, 4.06.
129.4, 134.2, 137.3, 158.0. Anal. Calcd for
C25H33NO4S
(443.60): C, 67.69; H, 7.50; N, 3.16. Found: C, 67.75; H, 7.46;
N, 3.20.
Da ta for (4R,1′S)-3-[1-(P h en ylsu lfon yl)-3-m eth ylbu tyl]-
4,5,5-tr ip h en yloxa zolid in -2-on e (9l): purified by crystal-
lization; yield 68%; mp 123 °C; [R]20D ) -123.3 (c 1.8, CHCl3);
IR (cm-1, KBr) 1690, 1377, 1133; 1H NMR δ (ppm) 0.16 (d,
3H, J ) 6.7 Hz), 0.77 (d, 3H, J ) 6.4 Hz), 1.16-1.30 (m, 2H),
1.74-1.72 (m, 1H), 5.19 (dd, 1H, J ) 10.8, 2.3 Hz), 6.29 (s,
Da ta for (4R,1′S)-5,5-Dim eth yl-3-(1-h ep tylbu t-3-en yl)-
4-p h en yloxa zolid in -2-on e (11k ): yield 79%; oil; [R]20
)
D
-22.4 (c 4.6, CHCl3); IR (cm-1, neat) 1695; H NMR δ (ppm)
0.87 (t, 3H, J ) 6.5 Hz), 0.94 (s, 3H), 1.10-1.37 (m, 10H), 1.53
(s, 3H), 1.55-1.71 (m, 2H), 1.75-1.96 (m, 1H), 2.24-2.46 (m,
1

2994 J . Org. Chem., Vol. 67, No. 9, 2002
Marcantoni et al.
1H), 3.35-3.52 (m, 1H), 4.36 (s, 1H), 4.97-5.04 (m, 2H), 5.59-
5.57 (m, 1H), 7.34-7.40 (m, 5H); 13C NMR δ (ppm) 14.1, 22.6,
24.0, 26.8, 29.1, 29.3, 31.8, 37.8, 55.0, 69.5, 80.9, 113.7, 117.6,
(ppm) 17.6, 19.0, 19.3, 31.5, 36.9, 55.7, 66.5, 117.4, 127.96,
127.98, 128.3, 128.6, 134.8, 136.8, 156.5. Anal. Calcd for C15H21
-
NO2 (247.33): C, 72.84; H, 8.56; N, 5.66. Found: C, 72.89; H,
8.53; N, 5.71.
128.5, 128.8, 129.0, 135.6, 137.0, 157.4. Anal. Calcd for C22H33
-
NO2 (343.51): C, 76.92; H, 9.68; N, 4.08. Found: C, 76.86; H,
9.71; N, 4.12.
Da ta for (S)-Meth yl-1-P h en eth ylbu t-3-en ylca r ba m a te
(15): obtained by reductive cleavage of 11j; yield 77%; oil;
[R]20 ) -9.7 (c 2.5, CHCl3); IR (cm-1, neat) 3310, 1685; 1H
Da ta for (4R)-3-(1-Isobu tylbu t-3-en yl)-4,5,5-tr ip h en yl-
oxa zolid in -2-on e(11l): mixture of 1′S and 1′R (65.35) dia-
stereomers; yield 58%; mp 213 °C; [R]20D ) +61 (c 1.3, CHCl3);
D
NMR δ (ppm) 1.65-1.91 (m, 2H), 2.17-2.40 (m, 2H), 2.56-
2.81 (m, 2H), 3.69 (s, 3H), 3.75-3.88 (m, 1H), 4.64 (d, 1H, J )
8.9 Hz), 5.05-5.15 (m, 2H), 5.69-5.86 (m, 1H), 7.18-7.35 (m,
5H); 13C NMR δ (ppm) 32.1, 36.3, 39.3, 50.2, 51.8, 117.9, 125.7,
128.1, 128.2, 133.8, 141.5, 156.5. Anal. Calcd for C14H19NO2
(233.31): C, 72.07; H, 8.21; N, 6.00. Found: C, 72.13; H, 8.23;
N, 5.96.
1
IR (cm-1, KBr) 1693; H NMR (1′S) δ (ppm) 0.49 (d, 3H J )
6.4 Hz), 0.58 (d, 3H, J ) 6.4 Hz), 1.23-1.37 (m, 2H), 1.58-
1.69 (m, 1H), 1.99-2.10 (m, 1H), 2.16-2.27 (m, 1H), 3.61-
3.73 (m, m, 1H), 4.69-4.83 (m, 2H), 5.26 (s, 1H), 5.40-5.57
(m, 1H), 6.95-7.25 (m, 11H), 7.27-7.40 (m, 2H), 7.60-7.75
(m, 2H). Anal. Calcd for C29H31NO2 (425.57): C, 81.85; H, 7.34;
N, 3.29. Found: C, 81.84; H, 7.31; N, 3.33.
Da t a for (S)-Met h yl-1-h ep t ylb u t -3-en ylca r b a m a t e
(16): obtained by reductive cleavage of 11k ; yield 75%; mp
38 °C; [R]20D ) -15.1 (c 1.8, CHCl3); IR (cm-1, KBr) 3305, 1695;
1H NMR δ (ppm) 0.84 (t, 3H, J ) 6.7 Hz), 1.23-1.71 (m, 12H),
2.09-2.28 (m, 2H), 3.44-3.60 (m, 1H), 3.62 (s, 3H), 4.46 (d,
1H, J ) 8.0 Hz), 5.00-5.07 (m, 2H), 5.67-5.80 (m, 1H); 13C
NMR δ (ppm) 14.1, 22.6, 25.8, 29.2, 29.4, 31.8, 34.6, 39.5, 50.6,
51.9, 117.7, 134.3, 156.4. Anal. Calcd for C13H25NO2 (227.34):
C, 68.68; H, 11.08; N, 6.16. Found: C, 68.75; H, 11.01; N, 6.19.
Data for (S)-Meth yl-1-isobu tylbu t-3-en ylcar bam ate (19):
Da ta for (4R)-3-(1-Isobu tylbu t-3-en yl)-4-isop r op yloxa -
zolid in -2-on e (11m ): mixture of 1′S and 1′R (75:25) diaster-
eomers; yield 68%; oil; [R]20D ) +13.3 (c 1.8, CHCl3); IR (cm-1
,
1
neat) 1690; H NMR (1′S) δ (ppm) 0.87 (d, 3H, J ) 6.4 Hz),
0.89 (d, 3H, J ) 6.4 Hz), 0.93 (d, H, J ) 6.6 Hz), 0.95 (d, 3H,
J ) 6.7 Hz), 1.48-1.66 (m, 3H), 1.91-2.04 (m, 1H), 2.13-2.23
(m, 1H), 2.49-2.59 (m, 1H), 3.49-3.74 (m, 2H), 4.03 (dd, 1H,
J ) 8.9, 4.3 Hz), 4.09 (d, 1H, J ) 8.9 Hz), 5.01-5.12 (m, 2H),
5.71-5.79 (m, 1H). Anal. Calcd for C14H25NO2 (239.36): C,
70.25; H, 10.53; N, 5.85. Found: C, 70.21; H, 10.49; N, 5.88.
Gen er a l P r oced u r e for th e Red u ctive Clea va ge of th e
Oxa zolid in -2-on e Rin g. Allyl derivative 11 (2 mmol) was
dissolved in a mixture of THF (80 mL) and t-BuOH (10 mL),
and then Li shots (20 mmol) were added in one portion. After
the mixture was cooled to -78 °C, NH3 (100 mL) was
condensed, and the blue solution was stirred at this temper-
ature for 1 h. The reaction mixture was then quenched by
addition of solid NH4Cl (2 g) and warmed to room temperature,
and then the volume of the solvent was reduced to about 20
mL by evaporation at reduced pressure. Na2CO3 (2 N, 20 mL)
was added followed by the appropriate chloroformate (6 mmol),
the mixture was stirred overnight and then concentrated at
reduced pressure. The resulting aqueous solution was ex-
tracted with CH2Cl2 and then dried over MgSO4. After
evaporation of the solvent at reduced pressure, the crude
carbamate was purified by column chromatography (9:1 hex-
anes-ethyl acetate).
yield 82%; oil; [R]20 ) -28.3 (c 2.4, CHCl3); IR (cm-1, neat)
D
3300, 1690; 1H NMR δ (ppm) 0.85 (d, 3H, J ) 6.4 Hz), 0.86 (d,
3H, J ) 6.4 Hz), 1.18-1.25 (m 2H), 1.56-1.66 (m, 1H), 2.09-
2.23 (m, 2H), 3.60 (s, 3H), 3.64-3.78 (m, 1H), 4.42 (d, 1H, J )
7.8 Hz), 4.98-5.04 (m, 2H), 5.67-5.76 (m, 1H); 13C NMR δ
(ppm) 22.1, 23.1, 24.8, 40.1, 44.0, 48.7, 51.9, 117.8, 134.3, 156.5.
Anal. Calcd for C10H19NO2 (185.26): C, 64.83; H, 10.34; N, 7.56.
Found: C, 64.86; H, 10.30; N, 7.60.
Ack n ow led gm en t. We are greatly indebted to Pro-
fessor Elisabetta Foresti (University of Bologna) for the
X-ray crystallographic analysis of compound 9h and to
Professor Gianni Palmieri for semiempirical calcula-
tions. Financial support from the University of Cam-
erino (National Project “Stereoselezione in Sintesi Or-
ganica. Metodologie e Applicazioni”) is gratefully acknowl-
edged.
Da ta for (R)-Ben zyl-1-isop r op ylbu t-3-en ylca r ba m a te
Su p p or tin g In for m a tion Ava ila ble: Spectral and physi-
cal data for compounds not included in the Experimental
Section and X-ray molecular structure and crystal data of
compound 9h . This material is available free of charge via the
Internet at http://pubs.acs.org.
(14): obtained by reductive cleavage of 11i; yield 88%, oil; [R]20
D
) -27.1 (c 1.5, CHCl3); IR (cm-1, neat) 3300, 1690; 1H NMR δ
(ppm) 0.90 (d, 3H, J ) 6.7 Hz), 0.93 (d, 3H, J ) 6.7 Hz), 1.70-
1.82 (m, 1H), 2.08-2.15 (m, 1H), 2.21-2.28 (m, 1H), 3.53-
3.59 (m, 1H), 4.64 (d, 1H, J ) 9.5 Hz), 5.01-5.11 (m, 2H), 5.10
(s, 2H), 5.70-5.76 (m, 1H), 7.28-7.36 (m, 5H); 13C NMR δ
J O0162888