1-Oxa-3-azapentalen-2-ones as precursors of cis-2-amino alcohols: Synthesis from propargyl alcohols, CO2, and amines using an intramolecular amidoalkylation reaction of oxazolidin-2-ones

Article abstract of DOI:10.1023/A:1026154623110

The reaction of 5-methyl-5-(4-methyl-3-pentenyl)-4-methylene-1,3-dioxolan- 2-one with primary amines gives the corresponding 4-hydroxy-4-methyloxazolidin- 2-ones. These undergo an intramolecular amidoalkylation reaction to form 1-oxa-3-azapentalen-2-ones

Full text of DOI:10.1023/A:1026154623110

Chemistry of Heterocyclic Compounds, Vol. 39, No. 7, 2003
1-OXA-3-AZAPENTALEN-2-ONES AS PRECURSORS
cis
OF -2-AMINO ALCOHOLS: SYNTHESIS FROM
PROPARGYL ALCOHOLS, CO2, AND AMINES
USING AN INTRAMOLECULAR AMIDOALKYLATION
REACTION OF OXAZOLIDIN-2-ONES.
N. B. Chernysheva1, A. A. Bogolyubov1, V. V. Nesterov2, M. Yu. Antipin2, and V. V. Semenov1
The reaction of 5-methyl-5-(4-methyl-3-pentenyl)-4-methylene-1,3-dioxolan-2-one with primary amines
gives the corresponding 4-hydroxy-4-methyloxazolidin-2-ones. These undergo an intramolecular
amidoalkylation reaction to form 1-oxa-3-azapentalen-2-ones which are potential precursors of
cyclopentanyl cis-2-amino alcohols.
Keywords: 2-amino alcohols, 4-hydroxyoxazolidin-2-ones, 4-methylene-1,3-dioxolan-2-ones, 1-oxa-3-
azapentalen-2-ones, intramolecular amidoalkylation, X-ray structural analysis, stereoselectivity.
Several chiral 2-amino alcohols are of significant interest as components for the preparation of catalysts
for Diels–Alder [1], Michael [2], and enantioselective reduction [3] type asymmetric reactions. In addition,
2-amino alcohols show a broad spectrum of biological activity.
In this work we propose a simple route to the precursors of cyclopentanyl cis-2-amino alcohols via the
reaction of the dioxolanone 1a [4] with primary amines 2 which leads to the intermediate oxazolidinones 3 [5].
An intramolecular amidoalkylation of the oxazolidinones 3 in HCOOH then permits the preparation of the
azapentalenones 4 and 5 with cis-orientated methyl groups at the ring junctions. Compounds 4 and 5 are under
consideration as potential precursors of the cis-2-amino alcohols mentioned.
In addition to the indicated method for the synthesis of the oxazolidinones 3 [5] there also exist other
routes for the preparation of these substances. Despite the formation of side products, modest yields, and the
complexity of the procedure, several oxazolidinones 3 are more readily synthesized via addition of
organometallic compounds to oxazolidin-2,4-diones [6, 7]. A method has also been proposed for
4-methoxyoxazolidin-2-ones (materials related to the oxazolidinones 3) via the use of Sn- and Se-organic
compounds which give good yields and are stereospecific [8]. The amidoalkylation of 4-hydroxythiazolidin-2-
ones is covered by the review [8] but the amidoalkylation of the oxazolidinones 3 has seen little work other than
the articles referred to [6, 7] and our paper [10].
The reaction of the amines 2 with dioxolanones 1 occurs over 12-144 hours at room temperature to give
38-100% yields of the oxazolidinones 3a-g,i (3h was prepared at 110°C).
__________________________________________________________________________________________
1
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913;
e-mail: vs@cacr.ioc.ac.ru. 2 A. N. Nesmeyanov Institute of Organoelemental Compounds, Russian Academy of
Sciences, Moscow 117813; e-mail: mishan@xray.ineos.ac.ru. Translated from Khimiya Geterotsiklicheskikh
Soedinenii, No. 7, pp. 1067-1079, July, 2003. Original article submitted November 3, 2000.
0009-3122/03/3907-0925$25.00©2003 Plenum Publishing Corporation
925

HO
O
R
R
H2N R1
+
O
N
O
O
R1
2a–h
O
1a,b
3a–i
1 a R = Dhl, b R = Me, 2 a R1 = Bn, b R1 = 2-PyCH2, c R1 = NCCH2CH2, d R1 = CH2=CHCH2,
e R1 = HOCH2CH2, f R1 = Me2N, g R1 = Tzl, h R1 = 3-PyCH2; 3 a–c, e–i R = Dhl, d R = Me;
a R1 = Bn, b R1 = 2-PyCH2, c R1 = NCCH2CH2, d, e, R1 = CH2=CHCH2, f R1 = HOCH2CH2,
g R1 = Me2N, h R1 = Tzl, i R1 = 3-PyCH2
N
N
Dhl = Me2C=CHCH2CH2, Tzl =
N
Catalysis by a Lewis base (in our case NEt3) is needed for the less active N,N-dimethylhydrazine (2f)
1
and the amines 2c and 2g. The structure of the oxazolidinones 3 was confirmed by their H NMR spectra in
which signals for both the 4-OH and the 4-Me groups are present [5]. The benzyl-type methylene protons in the
oxazolidinones 3a,b,i are revealed as two doublets with a small spin-spin coupling due to the presence of an
asymmetric center at position 4 of the oxazolidinone ring. If there are two asymmetric centers in the molecule
1
(two epimers) the interpretation of the H NMR spectra becomes more difficult due to doubling of the signals.
Such a mixture of epimers appears on TLC as two spots. Their melting points are unclear (in addition, several
oxazolidinones of the type 3 are unstable and can lose water not only upon heating but even at room temperature
1
[5]). The mixture of epimers of 3a was chromatographically separated into the two epimers and their H NMR
spectra and melting points found to be different. Over one week in CDCl3 solution containing traces of DCl both
1
pairs are converted to the same product which was characterized by H NMR spectroscopy as 3-benzyl-5-
methyl-5-(4-methyl-3-pentenyl)-4-methyleneoxazolidin-2-one.
O
N
Bn
O
We have found that the amidoalkylation of the oxazolidinones 3 occurs at room temperature over
48-168 hours to give 26-96% yields of the azapentalenones 4a-e.
In the case of compounds 3d,e the allyl groups in position 3 of the oxazolidinone ring do not undergo
attack at the acyliminium center since this would demand a geometrically unfavored 5-endo-trig transition state
[11]. For the azapentalenone 4d an acylation of the β-hydroxyethyl group by the formyl residue is observed
(Scheme 1)
We have not attempted to establish the absolute configuration of the azapentalenones 4a-e but, based on
theoretical grounds [7, 11] and X-ray structural data for compound 5' (see later) we propose that the
azapentalenones 4a-e must have the indicated stereochemistry*. The methyl groups on the vicinal atoms of the
bicyclic fragment are cis-orientated and the propenyl group at position 5 is endo-orientated.
_______
* Compounds 4a-e are racemates since the starting dioxolanone 1a is also a racemate and so the
azapentalenones 5' and 5'' are also racemates and the material 4f'/4f'' is a mixture of epimers (see later).
926

Scheme 1
H
H
+
+
+HCOOH
3a, c, e-g
N
N
R
O
-
R
O
H O
2
O
B
O
A
-
H
H
H
6
OOCH
7
1
5
+
Me
CH
2
+
4a
-
N
O
HCOOH
2
4
N
O
N
R
R
O
3
R
O
C
O
D
O
4a-e
4 a R = PhCH2, b R = NCCH2CH2, c R = CH2=CHCH2, d R = HCOOCH2CH2, e R = Me2N
The reaction takes place by a standard mechanism. The acyliminium center reacts with the double bond
in the molecule A in such a way as to ensure maximum overlap of the molecular orbitals and minimization of
the energy in the newly formed ring upon transition to the three centered ion B. The molecule B is then
converted to the tertiary carbocation C having a five-membered ring. Although, from an energetic point of view,
the five-membered ring is comparable with a six-membered the latter is not formed because it would demand the
generation of the less stable secondary carbocation D. The stabilization of the tertiary carbocation C can occur
by two routes: elimination of a proton or the addition of the HCOO- anion. Formation of the unsaturated
azapentalenones 4a-e suggests that the rate of proton loss is much higher than the rate of addition of the
counterion. In all cases a loss of a proton from one of the methyl groups of the isopropyl carbocation C is
observed and not a proton of the cyclopentane ring. However, both the elimination of the proton and the
addition of the formate anion is observed if, in position 3 of the oxazolidinone ring, there is located a substituent
which can be protonated (with the exception of compound 4e where only the proton elimination occurs).
Hence the starting oxazolidinone 3b yields the four products 4f '/4f '', 5', and 5''. We were able to
separate compounds 5' and 5'' chromatographically but compounds 4f '/4f '' could only be isolated as a mixture
(according to 1H NMR the ration of 4' to 4'' was ~ 1:1). The 1H NMR data for the products of amidoalkylation
of oxazolidinones 3h,i suggest that products analogous to 4f '/4f '', 5', and 5'' are present in the reaction
mixtures. Evidently the formation of the fomyloxy derivatives 5 is due to the possibility of coordination of the
formate anion with the protonated pyridine ring. The carbocations E and F (analogs of C) can be stabilized both
by the loss of a proton and by the addition of the coordinated formate anion. Evidently the rates of both
processes are similar since the yields of 4f '+4f '' and 5'+5'' are comparable. The formation of the
stereoisomeric products 4f '/5' and 4f ''/5f '' are controlled by two opposing factors: the tendency towards
maximum overlap of the interacting molecular orbitals of the double bond and the acyliminium center on the
one hand and the repulsion of the two positively charged acyliminium ion and pyridinium ring centers on the
other. Since the yields of 4f '+5' and 4f ''+5'' are almost identical both factors are also most likely to be
comparable in the magnitude of their effects.
927

H
+
+
H
N
3b
N
O
O
-
-
NH HCOO
O
NH HCOO
O
+
+
E
F
-
-
HCOOH
HCOOH
HOCO
OCOH
O
N
N
O
O
N
N
O
O
4f'
O
4f''
O
5'
O
5''
N
N
N
N
The configuration of the ester 5' was determined by an X-ray structural method (Fig. 1). As expected,
the methyl groups on the vicinal atoms of the bicyclic fragment are cis-orientated and the 5-C(Me)2–O–CO–H
endo-orientated. The torsional angles C(22)–C(12)–C(11)–C(21) and C(13)–C(14)–C(15)–C(16) are 25.8(4) and -165.6(3)°
respectively. The oxazolidinone ring has a twist conformation with a deviation of atoms C(11) and C(12) of
0.218 Å and -0.186 Å respectively. The cyclopentane ring is a distorted envelope with a deviation of the C(13)
atom of 0.559 Å. The angle between the two annelated rings is 76°. Due to the weak C–H···O interaction at
C(18)–H(18)···O(20) (-x, 1/2 + y, 1/2 - z) [C(18)···O(20) 3.234(4), C(18)–H(18) 0.990(5), H(18)···O(20) 2.430(5) Å, angle
C(18)–H(18)···O(20) 138(3)°] the molecules form a spiral around the crystallographic b axis (Fig. 2).
Fig. 1. Azapentalenone 5'.
928

Fig. 2. Crystal lattice for the azapentalenone 5'.
Almost all of the remaining bond lengths d (Table 1) and angles ω (Tables 2 and 3) have expected
values [12]. Table 4 shows the atomic coordinates (×104) and isotropic thermal parameters (equivalent for non
hydrogen atoms).
The azapentalenone stereoisomers 5' and 5'' show different chemical shifts for the formyl and 3-CH2–
2'–Py group protons in their 1H NMR spectra (in addition, compound 5' is a solid material and 5'' an oil). On the
basis of the spectroscopic data the compound 5'' can be assigned the structure with an exo-orientated 5-C(Me)2–
O–CO–H substituent.
Dilution of the reaction mixture leads to an increased yield of the target products in agreement with
literature data. The yield of 4a increases from 54 to 65% when the initial concentration of the oxazolidinone 3a
is lowered from 0.111 to 0.055 mmol/ml. Mass spectroscopic data indicates that the side products isolated have
a doubled molecular weight for 3a minus two molecules of water. These are evidently dimers, the formation of
which has been discussed in [9].
TABLE 1. Bond Lengths in the Azapentalenone Molecule 5'
Bond
d, Å
Bond
d, Å
Bond
d, Å
O(10)–C(9)
O(10)–C(11)
O(17)–C(18)
O(17)–C(16)
O(19)–C(18)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(11)–C(13)
1.340(4)
1.482(4)
1.326(5)
1.468(4)
1.185(5)
1.366(6)
1.381(5)
1.516(5)
1.497(5)
C(11)–C(21)
O(20)–C(9)
N(1)–C(6)
N(1)–C(2)
N(8)–C(9)
1.503(5)
1.211(4)
1.327(4)
1.339(4)
1.339(4)
1.436(4)
1.559(4)
1.504(4)
1.578(4)
C(13)–C(14)
C(14)–C(15)
N(8)–C(12)
C(2)–C(3)
1.512(5)
1.531(5)
1.470(4)
1.355(6)
1.355(6)
1.550(5)
1.504(5)
1.531(5)
C(3)–C(4)
N(8)–C(7)
C(15)–C(16)
C(16)–C(23)
C(16)–C(24)
C(11)–C(12)
C(12)–C(22)
C(12)–C(15)
929

TABLE 2. Angles in the Azapentalenone Molecule 5'
Angle
ω, deg.
Angle
ω, deg.
C(9)–O(10)–C(11)
C(18)–O(17)–C(16)
C(6)–N(1)–C(2)
110.1(2)
121.6(3)
116.4(3)
121.6(3)
112.2(2)
126.0(3)
125.0(4)
117.8(4)
119.2(4)
119.5(4)
121.9(3)
106.5(3)
116.4(3)
111.8(3)
100.0(2)
114.3(3)
115.1(2)
111.5(3)
103.4(2)
104.8(3)
103.3(3)
C(14)–C(15)–C(16)
N(1)–C(6)–C(7)
C(5)–C(6)–C(7)
N(8)–C(7)–C(6)
113.9(3)
117.9(3)
120.2(3)
114.9(3)
127.6(3)
122.3(3)
110.0(3)
106.7(3)
107.4(3)
116.6(3)
101.9(2)
106.3(3)
120.7(3)
111.7(3)
109.9(3)
110.4(3)
102.0(2)
113.7(3)
108.7(3)
126.4(4)
C(9)–N(8)–C(7)
C(9)–N(8)–C(12)
C(7)–N(8)–C(12)
N(1)–C(2)–C(3)
C(4)–C(3)–C(2)
C(3)–C(4)–C(5)
C(4)–C(5)–C(6)
O(20)–C(9)–N(8)
O(20)–C(9)–O(10)
N(8)–C(9)–O(10)
O(10)–C(11)–C(13)
O(10)–C(11)–C(21)
C(13)–C(11)–C(21)
O(10)–C(11)–C(12)
C(14)–C(15)–C(12)
C(16)–C(15)–C(12)
O(17)–C(16)–C(23)
O(17)–C(16)–C(24)
C(23)–C(16)–C(24)
O(17)–C(16)–C(15)
C(23)–C(16)–C(15)
C(24)–C(16)–C(15)
O(19)–C(18)–O(17)
N(1)–C(6)–C(5)
C(13)–C(11)–C(12)
C(21)–C(11)–C(12)
N(8)–C(12)–C(22)
N(8)–C(12)–C(11)
C(22)–C(12)–C(11)
N(8)–C(12)–C(15)
C(22)–C(12)–C(15)
C(11)–C(12)–C(15)
C(11)–C(13)–C(14)
C(13)–C(14)–C(15)
TABLE 3. Basic Torsional Angles (τ) in the Azapentalenone Molecule 5'
Angle
τ, deg.
80.4(4)
-35.4(5)
15.6(5)
-167.7(3)
7.8(3)
Angle
τ, deg.
33.1(4)
C(9)–N(8)–C(7)–C(6)
N(1)–C(6)–C(7)–N(8)
N(8)–C(12)–C(15)–C(16)
C(9)–N(8)–C(12)–C(11)
C(7)–N(8)–C(12)–C(11)
C(9)–N(8)–C(12)–C(15)
C(7)–N(8)–C(12)–C(15)
O(10)–C(11)–C(12)–N(8)
C(13)–C(11)–C(12)–N(8)
C(21)–C(11)–C(12)–C(22)
O(10)–C(11)–C(12)–C(15)
C(11)–C(12)–C(15)–C(16)
C(18)–O(17)–C(16)–C(23)
C(18)–O(17)–C(16)–C(24)
C(18)–O(17)–C(16)–C(15)
C(12)–C(15)–C(16)–O(17)
C(12)–C(15)–C(16)–C(23)
C(12)–C(15)–C(16)–C(24)
C(16)–O(17)–C(18)–O(19)
-19.7(3)
155.7(3)
90.4(3)
-94.3(3)
22.6(3)
134.2(3)
25.8(4)
-96.4(3)
141.1(3)
-60.4(4)
62.5(5)
177.8(3)
53.6(4)
-66.8(4)
169.7(3)
-1.1(6)
C(7)–N(8)–C(9)–O(20)
C(7)–N(8)–C(9)–O(10)
C(12)–N(8)–C(9)–O(10)
C(11)–O(10)–C(9)–N(8)
C(9)–O(10)–C(11)–C(13)
C(9)–O(10)–C(11)–C(12)
C(7)–N(8)–C(12)–C(22)
C(13)–C(11)–C(12)–C(15)
O(10)–C(11)–C(13)–C(14)
C(12)–C(11)–C(13)–C(14)
C(11)–C(13)–C(14)–C(15)
C(13)–C(14)–C(15)–C(16)
C(13)–C(14)–C(15)–C(12)
N(8)–C(12)–C(15)–C(14)
C(11)–C(12)–C(15)–C(14)
9.0(4)
-131.9(3)
-20.5(3)
34.3(4)
15.2(3)
73.5(4)
-34.8(4)
40.3(4)
-165.6(3)
-30.3(4)
-98.5(3)
9.5(3)
Hence the azapentalenones 4 and 5 obtained have the indicated stereochemistry. All the stages of the
synthesis (dioxolanone 1 to oxazolidinone 3 to azapentalenones 4 and 5) are characterized by good yields, mild
conditions, and ready separation of products (moreover, the oxazolidinones 3 can be used without purification).
Hydrolysis of the azapentalenones 4 is the theme of subsequent publications; an example of the hydrolysis of
related compounds can be found in our work [10].
930

TABLE 4. Coordinates (×104) and Isotropic (Equivalent for Non-hydrogen
Atoms) Atomic Thermal Parameters in the Azapentalenone 5'
Atom
O(10)
O(17)
O(19)
O(20)
N(1)
N(8)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(9)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(18)
C(21)
C(22)
C(23)
C(24)
H(2)
x
y
z
U
087(2)
696(3)
-968(4)
2144(3)
964(3)
1975(2)
594(5)
-545(5)
-1334(5)
-990(4)
148(3)
7099(2)
9595(2)
9128(3)
5921(2)
7749(3)
7990(2)
7885(4)
8544(4)
9160(4)
9056(4)
8322(3)
8122(4)
6926(3)
8427(3)
8976(3)
8603(4)
8450(4)
9111(3)
8823(3)
9651(4)
8805(5)
10180(3)
7492(4)
2561(1)
1138(1)
250(2)
58(1)
53(1)
96(1)
68(1)
61(1)
40(1)
70(1)
68(1)
70(1)
60(1)
46(1)
51(1)
48(1)
47(1)
38(1)
56(1)
56(1)
42(1)
48(1)
64(1)
66(1)
51(1)
60(1)
2720(2)
4058(2)
2518(1)
4799(2)
5054(3)
4525(3)
3762(3)
3544(2)
2697(2)
2621(2)
2525(2)
2267(1)
1864(2)
1152(2)
1366(2)
818(2)
477(3)
2666(3)
4414(3)
2944(3)
5428(4)
4509(4)
3115(4)
1842(4)
-594(5)
4949(5)
2575(5)
1422(6)
2228(6)
1039(40)
-741(53)
-2118(52)
-1459(42)
29(44)
815(2)
3307(2)
2639(2)
808(2)
9258(5)
5(2)
77(1)
7451(35)
8537(42)
9669(41)
9381(32)
7368(45)
8780(34)
8083(37)
9471(36)
8836(38)
7536(47)
10013(32)
10351(42)
8393(33)
9752(47)
8630(32)
10759(31)
10467(31)
10043(40)
7371(31)
6991(50)
7253(34)
8657(57)
9093(31)
10137(48)
5141(22)
5572(30)
4641(26)
3376(22)
2566(25)
2404(21)
1879(21)
1922(20)
705(25)
1068(23)
1300(17)
1039(24)
3383(21)
3277(26)
3641(20)
2531(19)
2396(21)
3201(28)
460(21)
607(29)
1274(22)
-122(34)
-345(22)
56(26)
57(11)
98(15)
88(14)
55(11)
87(14)
58(10)
66(11)
57(10)
74(12)
92(14)
47(9)
85(13)
60(11)
85(14)
47(9)
55(10)
68(10)
78(12)
53(10)
104(17)
63(11)
134(22)
58(10)
84(13)
H(3)
H(4)
H(5)
H(71)
H(72)
H(131)
H(132)
H(141)
H(142)
H(15)
H(18)
H(211)
H(212)
H(213)
H(221)
H(222)
H(223)
H(231)
H(232)
H(233)
H(241)
H(242)
H(243)
-50(37)
6195(44)
5759(39)
5065(40)
4457(48)
3381(36)
-1131(49)
5779(45)
5199(46)
4215(42)
3319(39)
1754(43)
2508(43)
728(41)
2076(54)
923(44)
3003(68)
1447(43)
2487(48)
931

EXPERIMENTAL
1H NMR spectra were recorded on a Bruker WM-250 (250 MHz) instrument with TMS as internal
standard. IR Spectra were taken on a Perkin-Elmer 577 instrument (KBr) and mass spectra on a Kratos MS-30
instrument (direct introduction of the sample, 70 eV, 250°C). Flash chromatography on a dry column [13]
(Silufol 5/40 with benzene-ethyl acetate gradient elution) was used for separation of the mixtures. TLC was
performed on Silufol UV-254 plates with the systems: ethyl acetate–benzene, 4:1* (A), benzene–ethyl acetate
9:1* (B), benzene–ethyl acetate, 2:1* (C), benzene–ethyl acetate, 4:1* (D), acetonitrile–benzene, 2:1* (E), or
benzene–ethyl acetate, 1:1 (F). The cooling bath was acetone–dry ice with CH2Cl2/CHCl3 and extracts were
dried by filtration through glass wool.
Colorless crystals of the azapentalenone 5' (C18H24N2O4) were prepared by slow crystallization from
acetonitrile over 3 days. The crystals are orthorhombic: at 25°C: a = 9.310(5) Å, b = 10.907(6) Å,
c = 17.344(8) Å; V = 1761(2) Å3; dcalc = 1.254 g/cm3; Z = 4; P212121. 4242 Independent reflections were
obtained on a Siemens P3/PC diffractometer with λMoKα = 0.71072 Å, graphite monochromator, and θ/2θ
≤
scanning , θmax 28°. The structure was solved by a direct method and refined in a full matrix least squares
analysis in the anisotropic approximation for non-hydrogen atoms. Hydrogen atoms were localized directly in
difference Fourier synthesis and refined in the isotropic approximation. Final difference factors were
wR2 = 0.1270 for 2881 independent reflections (R1 = 0.052 for 1754 independent reflections with I 2σ(I)).
>
Calculations were carried out on an PC/AT-586 IBM computer using the SHELXTL PLUS and SHELXL-93
programs [14].
Dioxolanones 1a,b were prepared according to the method in [4].
3-Benzyl-4-hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)oxazolidin-2-one (3a). The dioxolanone
1a (5.88 g, 30 mmol) was added with stirring to a suspension of benzylamine hydrochloride (4a) (4.60 g,
32 mmol) and sodium hydroxide (1.28 g, 32 mmol) in water (10 ml). After 24 h at room temperature, the
mixture was extracted with chloroform (25 ml, then 15 ml). The combined extracts were washed with water to
neutral pH, filtered through glass wool, and the solvent was evaporated. The dark oil obtained was triturated
with hexane (4 ml) with cooling. The crystals obtained were washed with hexane (3 ml) to give white crystals
(7.35 g, 81%); mp 70-72°C. 0.51 g of the crystals were separated chromatographically to give 0.13 g (26%) of
the first epimer and 0.30 g (58%) of the second epimer. The first epimer had mp 102-107°C and Rf 0.47 (system
B) (twice). Mass spectrum, m/z (I, %): 303 (M+ 6.7), 204 (26.2), 203 (62.8), 153 (47.8), 128 (21.5). IR spectrum,
1
ν, cm-1: 1730, 3350. H NMR spectrum (CDCl3), δ, ppm (J, Hz): (1.22 (3H, s), 1.45 (3H, s), 4,5-CH3); (1.40-
1.73 (2H, m), 2.30-2.50 (2H, m), 4-CH2CH2); (1.60 (3H, s), 1.66 (3H, s), CH=CCH3)2); 3.87 (1H, s, 4-OH),
(4.32 (1H, d, J = 15.0), 4.65 (1H, d, J = 15.0), 3-CH2Ph); 5.06 (1H, t, CH=C(CH3)2); 7.22-7.49 (5H, m, Ph). The
second epimer had mp 84-87°C and Rf 10.25 (system B) (twice). The IR and mass spectrum of the second epimer
agreed with those of the first epimer. H NMR spectrum (CDCl3), δ, ppm (J, Hz): (1.24 (3H, s), 1.33 (3H, s),
4,5-CH3); (1.58-1.99 (2H, m), 2.07-2.23 (2H, m), 4-CH2CH2); (1.59 (3H, s), 1.66 (3H, s), CH=C(CH3)2); 3.60
(1H, s, 4-OH), (4.33 (1H, d, J = 17.8), 4.66 (1H, d, J = 17.8), 3-CH2Ph); 5.12 (1H, t, CH=C(CH3)2); 7.25-7.48
(5H, m, Ph). The dehydration product from both epimers had the following data: 1H NMR spectrum (CDCl3), δ,
ppm (J, Hz): (1.51 (3H, s), 1.54 (3H, s), CH=C(CH3)2); 1.70-2.16 (4H, m, 4-CH2CH2); 3.95 (1H, d, J = 3.7);
4.09 (1H, d, J = 3.7), 4.60 (1H, d, J = 15.5), 4.72 (1H, d, J = 15.5), 3-CH2-Ph); 5.06 (1H, t, CH=C(CH3)2); 7.24-
7.40 (5H, m, Ph).
4-Hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)-3-[(2-pyridyl)methyl]oxazolidin-2-one (3b).
A
solution of 2-aminomethylpyridine (2b) (2.71 g, 25.1 mmol) in dichloromethane (5 ml) was added to a solution
of dioxolanone 1a (4.90 g, 25 mmol) in dichloromethane (15 ml) and held for 24 h at room temperature. The
_______
* Plus 1-2 drops of cyclohexane.
932

reaction mixture was diluted with dichloromethane (10 ml), filtered through glass wool, and the solvent was
evaporated. The light-brown oil was carefully dried in vacuo to yield a viscous oil (7.50 g, 99%) which was
chromatographically pure (Rf 0.73, system E). Mass spectrum, m/z, (I, %): 304 (M+ 1.1), 205 (53.0), 204 (89.4),
173 (52.7), 162 (56.0). IR spectrum, ν, cm-1: 1750, 3360. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.18
(3H, s), 1.29 (3H, s), 4,5-CH3): (1.43-1.85 (2H, m), 1.97-2.20 (2H, m), 4-CH2CH2); (1.60 (3H, s), 1.68 (3H, s),
CH=C(CH3)2); (4.35 (1H, d, J = 17.6), 4.51 (1H, d, J = 17.6), 3-CH2-2'-Py): 5.12 (1H, t, CH=C(CH3)2); 6.34
(1H, s, 4-OH); 7.23-7.40 (2H, m, 3',5'-HPy); 7.79 (1H, t, 4'-Py); 8.51 (1H, d, J = 5.3, 6'-HPy).
3-(2-Cyanoethyl)-4-hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)oxazolidin-2-one (3c). The
β-aminopropionitrile 2c (2.10 g, 30 mmol) and 3-4 drops of triethylamine were added to a solution of the
dioxolanone 1a (5.88 g, 30 mmol) in dichloromethane (20 ml) and held for 144 h at room temperature. The
solvent was evaporated and the residue was triturated with hexane (4 ml). The precipitate formed was washed
with hexane (2 × 5 ml) and crystallized from ether–hexane (4:1) to yield white crystals (7.54 g, 95%);
mp 93-102°C and Rf 0.54 (system F) (twice). Mass spectrum, m/z (I, %): 266 (M+ 1.7), 167 (13.2), 166 (36.2),
125 (10.8), 108 (43.1). IR spectrum, ν, cm-1: 1740, 3350. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.25,
1.30 (3H, 2s), 1.34, 1.36 (3H, 2s), 4,5-CH3); (1.46-1.76 (2H, m), 1.96-2.17 (2H, m), 4-CH2CH2), (1.57, 1.58 (3H,
2s), 1.62, 1.63 (3H, 2s), CH=C(CH3)2); 2.60-2.75 (2H, m, 3-CH2CH2CN); 3.35 (2H, t, 3-CH2CH2CN); 5.03-5.17
(1H, m, CH=C(CH3)2); 6.11 (1H, s, 4-OH).
3-Allyl-4-hydroxy-4,5,5-trimethyloxazolidin-2-one (3d). Allylamine 2d (2.28 g, 40 mmol) was added
to a solution of dioxolanone 1b (5.12 g, 40 mmol) in dichloromethane (20 ml) with cooling to room
temperature. After 12 h the solvent was evaporated and the partially crystallizing colorless oil was washed with
hexane–benzene 10:1 (3 × 3 ml) to give white crystals (7.40 g, 100%); mp 50-52°C, Rf 0.35 (system F). Mass
spectrum, m/z (I, %): 185 (M+ 19.5), 168 (20.0), 167 (64.8), 127 (21.9), 123 (56.4). IR spectrum, ν, cm-1: 1740,
1
3320. H NMR spectrum (CDCl3), δ, ppm (J, Hz): (1.36 (3H, s), 1.37 (3H, s), 1.47 (3H, s), 4,5,5-CH3);
3.78-4.03 (2H, m, 3-CH2=CHCH2); 3.91 (1H, s, 4-OH); 5.15 (1H, dd, J = 1.0, J = 9.6), 5.25 (1H, dd, J = 1.0,
J = 18.4),3-CH2=CHCH2); 5.80-6.00 (1H, m, 3-CH2=CHCH2).
3-Allyl-4-hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)oxazolidin-2-one (3e). Allylamine (2d)
(1.71 g, 30 mmol) was added to a solution of the dioxolanone 1a (5.88 g, 30 mmol) in dichloromethane (20 ml).
After 96 h at room temperature, the solvent was evaporated, hexane (10 ml) was added with trituration and
cooling, and the precipitated crystals were washed with hexane (3 × 3 ml) to give snow-white crystals (4.80 g,
63%). The substance did not have a sharp mp but melted in the range 40-70°C; Rf 0.22, 0.47 (system D) (twice).
Mass spectrum, m/z (I, %): 253 (M+ 2.9), 154 (35.6), 111 (64.5), 108 (72.5), 85 (34.7). IR spectrum, ν, cm-1:
1
1725, 3330. H NMR spectrum (CDCl3), δ, ppm (J, Hz); (1.36 (3H, s), 1.42 (3H, s), 4,5-CH3); 1.50-1.78 (2H,
m), 2.03-2.28 (2H, m), 4-CH2CH2); (1.60 (3H, s), 1.69 (3H, s), CH=C(CH3)2); 3.78-4.00 (2H, m,
3-CH2=CHCH2); 3.87 (1H, s, 4-OH); 5.08 (1H, t, CH=C(CH3)2); (5.15 (1H, dd, J = 1.0, J = 8.8), 5.22 (1H, dd,
J = 1.0, J = 17.7), 3-CH2=CHCH2); 5.62-5.92 (1H, m, 3-CH2=CHCH2).
3-Dimethylamino-4-hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)oxazolidin-2-one (3g). Dioxolanone
1a (5.40 g, 27.55 mmol) was added to N,N-dimethylhydrazine 2f (2.07 g, 34.44 mmol) with cooling to room
temperature and triethylamine (2 ml) was added. After 96 h at room temperature the crystals were dissolved in
benzene (10 ml). The solvent and traces of 2f and triethylamine were evaporated at 50-60°C under reduced
pressure. The pasty precipitate was mixed with ether (10 ml) with vigorous stirring at 7-10°C and filtered. The
product was washed with cold ether (3 × 5 ml) to give 3.52 g of 3g as white, scaly crystals. The combined
mother liquors were allowed to evaporate in air to give an additional 0.52 g of 3g and overall yield of white
crystals of 4.04 g (57%); mp 84-87°C, Rf 0.43 (system C). Mass spectrum, m/z (I, %): 256 (M+ 3.5), 151 (18.5),
104 (31.6), 87 (22.0), 86 (100.0). IR spectrum, ν, cm-1: 1710, 3320. 1H NMR spectrum (CDCl3), δ, ppm (J, Hz);
(1.32 (3H, s), 1.46 (3H, s), 4,5-CH3); (1.61 (3H, s), 1.69 (3H, s), CH=C(CH3)2); (1.70-1.90 (2H, m), 2.05-2.18
(2H, m) 4-CH2CH2); 2.85 (6H, s, N(CH3)2); 5.11 (1H, t, CH=C(CH3)2).
933

4-Hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)-3-(1,2,4-triazol-4-yl)oxazolidin-2-one (3h).
A
mixture of the 4-amino-1,2,4-triazole 2g (1.68 g, 20 mmol), dioxolanone 1a (3.96 g, 20.2 mmol), triethylamine
(0.5 ml) and DMF (0.5 ml) was heated under reflux for 24 h at 110°C, and then cooled to room temperature.
The reaction mixture was triturated with ether (10 ml) to give crystals which were washed with ether (4 × 5 ml).
A white powder was obtained (2.15 g, 38%); mp 122-129°C, Rf 0.40, 0.85 (system A). Mass spectrum, m/z
(I, %): 280 (M+ 1.5), 151 (20.0), 129 (15.0), 111 (18.3), 110 (32.6). IR spectrum, ν, cm-1: 1770, 3320. 1H NMR
spectrums (DMSO-d6), δ, ppm (J, Hz): (1.27, 1.28 (3H, 2s), 1.48, 1.53 (3H, 2s), 4,5-CH3); (1.67 (3H, s), 1.69
(3H, s), CH=C(CH3)2); (1.70-1.98 (2H, m), 2.00-2.25 (2H, m), 4-CH2CH2); 5.16 (1H, t, CH=C(CH3)2); 7.00 (1H,
s, 4-OH); 8.68 (2H, s, 3',5'-HHet).
4-Hydroxy-4,5-dimethyl-5-(4-methyl-3-pentenyl)-3-[(3-pyridyl)methyl]oxazolidin-2-one (3i).
A
solution of 3-aminomethylpyridine 2h (2.71 g, 25.1 mmol) in dichloromethane (5 ml) was mixed with a solution
of the dioxolanone 1a (4.90 g, 25 mmol) in dichloromethane (15 ml). After holding for 72 h at room temperature
the reaction mixture was diluted with dichloromethane (10 ml). The solution was filtered through glass wool.
After evaporation of solvent, the substance formed was crystallized from benzene–hexane 4:1 (9.5 ml) to yield a
yellow powder (6.76 g, 89%); mp 93-102°C, Rf 0.20, 0.45 (system E). Mass spectrum, m/z (I, %): 276 (M+ 8.4),
204 (29.2), 111 (14.1), 94 (10.5), 93 (100.0). IR spectrum, ν, cm-1: 1770, 3320. 1H NMR spectrum (DMSO-d6),
δ, ppm (J, Hz): (1.21, 1.23 (3H, 2s), 1.30 (3H, s), 4,5-CH3); (1.42-1.63 (2H, m), 1.92-2.17 (2H, m), 4-CH2CH2);
(1.44, 1.50 (3H, 2s), 1.60, 1.62 (3H, 2s), CH=C(CH3)2); (4.30 (1H, d, J = 17.3), 4.63 (1H, d, J = 17.3),
3-CH2-3'-Py); 5.10 (1H, t, CH=C(CH3)2); 6.10 (1H, s, 4-OH), 7.36 (1H, t, 5'-HPy), 7.62 (1H, d, J = 7.8, 4'-HPy);
7.98 (1H, d, J = 6.2 Hz, 6'-HPy); 8.56 (1H, t, 2'-HPy).
General Method for the Preparation of the Azapentalenones 4 and 5. The corresponding
oxazolidinone 3 (2-10 mmol) was dried under vacuo over P2O5 for one day, dissolved in absolute formic acid
(3 ml of the acid to 0.1 g of 3 if no other ratio is indicated), and the mixture was allowed to stand for the
necessary time at room temperature (TLC monitoring). The acid was evaporated under reduced pressure, and
the reaction mixture was dissolved in chloroform or dichloromethane (8-10 mmole of the mixture per 100 ml of
solvent). The product was washed with a saturated solution of sodium bicarbonate (20 ml), saturated sodium
chloride solution (20 ml) and then with water (20 ml). The solution was then filtered through glass wool and the
solvent evaporated. After these general stages a specific purification of the reaction mixture followed.
3-Benzyl-3a,6a-dimethyl-4-isopropenylhexahydro-1-oxa-3-azapentalen-2-one (4a) was obtained by
the general method from the oxazolidinone 3a (1.82 g, 6 mmol) over 168 h. The reaction mixture was triturated
with hexane (4 ml) with cooling and the crystals formed were washed with hexane (4 × 5 ml) to give a white
powder (1.10 g, 65%); mp 90-92°C, Rf 0.48 (system B). Mass spectrum, m/z (I, %): 285 (M+ 2.5), 204 (12.7),
203 (51.7), 92 (19.8), 91 (100.0). IR spectrum, ν, cm-1: 1640, 1735. 1H NMR spectrum (CDCl3), δ, ppm (J, Hz):
(1.10 (3H, s), 1.33 (3H, s), 1,4a-CH3); (1.48-1.73 (2H, m), 1.92-2.08 (1H, m), 2.17 (1H, dd), 2.32 (1H, dd)
5-7-H); 1.90 (3H, s, 5-C(CH2)(CH3)); 4.02 (1H, d, J = 17.4), 4.82 (1H, d, J = 17.4), 4-CH2Ph); (4.48 (1H, d,
J = 1.0), 5.08 (1H, d, J = 1.0), 5-C(CH2(CH3)); 7.18-7.24 (5H, m, Ph). Found, %: C 75.98; H 8.10; N 4.92.
C18H23NO2. Calculated, %: C 75.75; H 8.12; N 4.91.
3-(2-Cyanoethyl)-4-isopropenyl-3a,6a-dimethylhexahydro-1-oxa-3-azapentalen-2-one (4b) was
prepared from oxazolidinone 3c (2.13 g, 8 mmol) over 72 h. The reaction mixture was triturated with hexane
(4 ml) with cooling and the crystals formed were washed with hexane (4 × 5 ml) to give white crystals (1.90 g,
96%); mp 91-93°C, Rf 0.53 (system F). Mass spectrum, m/z (I, %): 248 (M+ 2.2), 167 (51.7), 166 (100.0), 126
(34.7), 123 (27.4). IR spectrum, ν, cm-1: 1640, 1725, 2263. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.35
(3H, s), 1.42 (3H, s), 1,4a-CH3); (1.52-1.86 (3H, m), 1.87-2.08 (1H, m), 2.35 (1H, dd), 5-7-H); 1.80 (3H, s,
5-C(CH2)(CH3)); 2.54-2.88 (2H, m, 4-CH2CH2); (3.08-3.22 (1H, m), 3.25-3.35 (1H, m) 4-CH2CH2); (4.90 (1H,
d, J = 1.0), 5.00 (1H, d, J = 1.0 ), 5-C(CH2(CH3)). Found, %: C 67.51; H 8.14; N 11.31. C14H20N2O2.
Calculated, %: C 67.71; H 8.12; N 11.28.
934

3-Allyl-4-isopropenyl-3a,6a-dimethylhexahydro-1-oxa-3-azapentalen-2-one (4c) was prepared from
the oxazolidinone 3e (2.02 g, 8 mmol) over 95 h. The reaction product was triturated with hexane (4 ml) with
cooling and the crystals which precipitated were washed with hexane (4 × 5 ml) to give a white powder (0.57 g,
30%). The substance did not show a sharp mp but melted in the range 51-64°C, Rf 0.60 (system D). Mass
spectrum, m/z, (I, %): 235 (M+ 2.5), 153 (18.4), 152 (76.0), 122 (13.9), 112 (27.4). IR spectrum, ν, cm-1: 1640,
1
1730. H NMR spectrum (CDCl3), δ, ppm (J, Hz): (1.33 (3H, s), 1.37 (3H, s), 1,4a-CH3), (1.44-1.70 (2H, m),
1.84-2.00 (1H, m), 2.13 (1H, dd), 2.27 (1H, dd), 5-7-H); 1.80 (3H, s, 5-C(CH2)(CH3); (3.50 (1H, dd, J = 7.4,
J = 14.7), 4.02 (1H, m), 4-CH2=CHCH2); (4.92 (1H, d, J = 1.0), 5.00 (1H, d, J = 1.0), 5-C(CH2)(CH3)); 5.08
(2H, dd, J = 1.0, J = 5.9), 5.15 (1H, dd, J = 1.0, J = 14.0), 4- CH2=CHCH2); 5.70-5.88 (1H, m, 4-CH2=CHCH2).
3-(2-Formyloxyethyl)-4-isopropenyl-3a,6a-dimethylhexahydro-1-oxa-3-azapentalen-2-one (4d). A
solution of dioxolanone 1a (1.74 g, 8.87 mmol) and ethanolamine 2e (0.54 g, 8.87 mmol) in dichloromethane
(15 ml) was allowed to stand for 48 h at room temperature (TLC monitoring) and the solvent was evaporated.
The dried residue (3f) was dissolved in absolute formic acid and left for 48 h at room temperature. The mixture
was then worked up as described in the general method. The product obtained was purified as in the case of 4b
to give 1.63 g, (69%) of white crystals; mp 69-71°C, Rf 0.54 (system F). Mass spectrum, m/z, (I, %): 267
1
(M+ 1.7), 186 (20.7), 185 (59.2), 140 (13.0), 96 (26.8). IR spectrum, ν, cm-1: 1640, 1720. H NMR spectrum
(CDCl3), δ, ppm (J, Hz): (1.36 (3H, s), 1.37 (3H, s), 1,4a-CH3); (1.45-1.60 (2H, m), 1.90 (1H, dd), 2.13 (1H,
dd), 2.39 (1H, dd), 5-7-H); 1.88 (3H, s, 5-C(CH2)(CH3)); (3.11-3.27 (1H, m), 3.52-3.66 (1H, m),
4-CH2CH2OCOH); 4.20-4.35 (2H, m, 4-CH2CH2OCOH); (4.91 (1H, d, J = 1.0 ), 5.01 (1H, d, J = 1.0 ),
5-C(CH2)(CH3)); 8.05 (1H, s, 4-CH2CH2OCOH). Found, %: C 63.08; H 7.94; N 5.22. C14H21N2O4.
Calculated, %: C 62.90; H 7.92; N 5.24;
3-Dimethylamino-4-isopropenyl-3a,6a-dimethylhexahydro-1-oxa-3-azapentalen-2-one (4e) was
prepared from oxazolidinone 3e (2.56 g, 10 mmol) in formic acid (34 ml) over 120 h at room temperature. The
colorless viscous product was dissolved in boiling hexane (10 ml) and allowed to cool and it crystallized over
24 h at room temperature. The precipitated crystals were filtered off and washed with hexane (3 × 2 ml) to give
4e (1.0 g). The washings and mother liquors were combined. The liquors from two experiments were evaporated
and the residue (1.44 g) was purified by chromatography followed by recrystallization from hexane (2 ml) and
washing with cold hexane (2 × 1 ml) to give 4e (0.62 g, 43% of the weight of evaporated liquors) as a white
powder (4e). The overall yield from one experiment is 1.00 + 0.62/2 = 1.31 g (55%); mp 111-113°C, Rf 0.4
(system C). Mass spectrum, m/z (I, %): 238 (M+ 11.8), 196 (13.6), 145 (13.7), 137 (50.1), 125 (11.1).
1
IR spectrum, ν, cm-1: 1640, 1735. H NMR spectrum (CDCl3), δ, ppm (J, Hz): (1.34 (3H, s), 1.49 (3H, s),
1,4a-CH3); 1.50-1.94 (5H, m), 5-7-H); 2.00 (3H, s, 5-C(CH2)(CH3)), (2.73 (3H, s), 2.80 (3H, s), N(CH3)2); (4.86
(1H, d, J = 1.0 ), 4.93 (1H, d, J = 1.0 ), 5-C(CH2)(CH3)). Found, %: C 65.31; H 9.32; N 11.78. C13H22N2O2.
Calculated, %: C 65.51; H 9.30; N 11.75.
cis,trans
4-
(4f'/4f''),
pentalen-2-one (5') and its
-Isopropenyl-3a,6a-dimethyl-3-[(2-pyridyl)methyl]hexahydro-1-oxaazapentalen-2-one
endo
3a,6a-Dimethyl-4-
exo
-(methyl-1-formyloxyethyl)-3-[(2-pyridyl)methyl]hexahydro-1-oxaaza-
isomer 5''
were obtained by the general method from oxazolidinone
3b
(2.13 g,
7.29 mmol) over 48 h as a dark viscous oil (2.40 g) showing three spots on TLC (Rf 0.56 for 4',4'', 0.45 for 5',
and 0.3 for 5'', system F). The product was triturated with a mixture of ether–hexane (1:1, 10 ml). The solvent
was cooled, decanted off and these two operations were repeated three more times to yield 1.17 g of crystals.
Crystallization from ether–hexane gave 5' (0.86 g, 38%) as slightly brownish crystals. The combined liquors
were evaporated and the residue was separated by chromatography to give 4f'/4f'' (0.62 g, 31%, as an oil) and
5'' (0.58 g, 26%, as an oil). The overall yield of 4f'/4f'', 5' and 5'' was 95%.
Azapentalenones 4f'/4f'' 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.09, 1.21 (3H, 2s), 1.49 (3H,
s), 1,4a-CH3); 1.05-2.48 (5H, m, 5-7-H); 1.61, 1.89 (3H, 2s, 5-C(CH2)(CH3)), {[4.13 (d, J = 16.7 ), 4.62 (d,
J = 16.7 )], [4.49 (d, J = 16.7 ), 4.85 (d, J = 16.7 )], 2H 4-CH2-2-Py}; (4.95 (1H, d, J = 1.0 ), 5.06 (1H, d,
J = 1.0 ), 5-C(CH2)(CH3))); 7.16-7.32 (2H, m, 3',5'-HPy); 7.66-7.80 (1H, m, 4'-HPy); 8.41-8.56 (1H, m, 6'-HPy).
935

Azapentalenone 5' Mp 144-146°C. Mass spectrum, m/z (I, %): 332 (M+ 0.4), 287 (5.1), 243 (1.1), 227
(1.1), 204 (18.4). IR spectrum, ν, cm-1: 1745. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.24 (3H, s), 1.40
(3H, s), 1,4a-CH3); (1.52 (3H, s), 1.63 (3H, s), 5-C(CH3)2OCHO); (1.60-1.80 (3H, m), 1.90-2.10 (1H, m),
2.16-2.30 (1H, m), 5-7-H); (4.40 (1H, d, J = 16.1 ), 4.56 (1H, d, J = 16.1 ), 4-CH2-2-Py); 7.21 (1H, dd, J = 5.6,
J = 8.1, 4'-HPy); 7.30 (1H, d, J = 8.1, 3'-HPy ); 7.72 (1H, t, 5'-HPy); 8.36 (1H, s, 5-C(CH3)2OCOH); 8.48 (1H, d,
J = 6.4, 6'-HPy ). Found, %: C 65.23; H 7.26; N 8.41. C18H24N2O4. Calculated: C 65.04; H 7.28; N 8.43.
Azapentalenone 5'' The mass spectrum of this compound was identical to that of 5'. IR spectrum,
ν, cm-1: 1730. 1H NMR spectrum (DMSO-d6), δ, ppm (J, Hz): (1.26 (3H, s), 1.36 (3H, s), 1,4a-CH3); (1.50-1.70
(1H, m), 1.80-2.20 (3H, m). 2.52 (1H, dd), 5-7-H); (1.51 (3H, s), 1.59 (3H, s), 5-C(CH3)2OCOH); (4.48 (1H, d,
J = 21.9 ), 4.60 (1H, d, J = 21.9 ), 4-CH2-2-Py); 7.24 (1H, dd, J = 6.6, J = 9.8, 4'-HPy); 7.36 (1H, d, J = 9.8,
3'-HPy), 7.71 (1H, t, 5'-HPy); 8.16 (1H, s, 5-C(CH3)2OCOH); 8.50 (1H, d, J = 5.5, 6'-HPy).
This work was carried out with the financial support of the RFFR, grants No. 97-03-33783,
96-15-97367, and 96-07-89187
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