Synthesis of 9- and 10-membered macrolactones by selective ozonolysis of 1,4-diazaphenanthrene derivatives

Article abstract of DOI:10.1016/j.tet.2004.10.075

9- and 10-membered macrolactones bearing benzo and diazine rings were obtained by chemoselective ozonolysis of dihydrofuran and pyran 1,4-diazaphenathrene derivatives. This is the first example of preparation of macrolactones by chemoselective ozonolysis of an enol double bond shared by aromatic and heterocyclic rings.

Full text of DOI:10.1016/j.tet.2004.10.075

Tetrahedron 61 (2005) 437–445
Synthesis of 9- and 10-membered macrolactones by selective
ozonolysis of 1,4-diazaphenanthrene derivatives
a,b,
a,b,
Elisa Perez-Sacau, Jorge Soto-Delgado,a,b Ana Estevez-Braun
a,b
´
and Angel G. Ravelo
*
*
´
´
a
´ ´ ´
Instituto Universitario de Bio-Organica ‘Antonio Gonzalez’, Avda. Astrofısico Fco. Sanchez 2, 38206, La Laguna, Tenerife, Spain
´
´ ´
Instituto Canario de Investigacion del Cancer, Hospital Universitario de La Candelaria, 38010, Tenerife, Spain
b
Received 9 August 2004; revised 18 October 2004; accepted 21 October 2004
Abstract—9- and 10-membered macrolactones bearing benzo and diazine rings were obtained by chemoselective ozonolysis of
dihydrofuran and pyran 1,4-diazaphenathrene derivatives. This is the first example of preparation of macrolactones by chemoselective
ozonolysis of an enol double bond shared by aromatic and heterocyclic rings.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
compounds with fused benzo and diazine moieties. The
presence of diaza heterocyclic rings close to the ion-binding
macrolactone moiety opens attractive possibilities, offering
the potential of coupling DNA-damage with ion-binding
properties.
Macrolides are an attractive class of compounds that have
shown a wide variety of interesting bioactivities.1 Some
representative examples are leucascandrolide,2 epothilone,3
erythromycin,4 or salicylihalamide.5 Among the 9- and
10-membered macrolactones, the antibiotic activity of
lustromycin,6 the anti-proliferative properties of api-
cularen,7 or the bacterial DNA primase inhibitory activity
of Sch 642305,8 stand out. This variety of activities may be
due to the fact that macrolides often show multiple low-
energy conformations. Changes in the position and nature of
the substituents can alter the free energy penalty for
distortion of one of these small molecules upon binding to
a protein target.9 Consequently, the ability of these host
molecules to bind guests is often very specific, enabling the
host to recognize just one molecule or ion in a mixture.
2. Results and discussion
Scheme 1 shows the retrosynthetic pathway toward the
macrolactones. It involves ozonolysis, condensation and
cyclization processes.
On the other hand, there are many examples of natural and
synthetic phenazines which exhibit diverse activities like
antimalarial,10 trypanocidal,11 fungicidal,12 or antiplate-
let.13 These heterocyclic compounds fulfill the fundamental
physicochemical requirements for DNA intercalation,
exhibiting antitumor activity in leukaemia and solid
tumours. Some benzophenazines are dual inhibitors of
topoisomerase I and II, two key enzymes that affect the
topology of DNA at different points in the cell cycle.14
This paper describes the preparation of macrocyclic
Scheme 1.
Keywords: 1,4-Diazaphenanthrene derivatives; Ozonolysis; 9- and 10-
membered macrolactones.
The initial precursors, lapachol 1 and lawsone 2, are
bioactive naphthoquinones isolated from plants of the
* Corresponding authors. Tel.: C34 922 318576; fax: C34 922 318571;
e-mail addresses: aestebra@ull.es; agravelo@ull.es
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.075

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
438
Scheme 2. Reagents and conditions: (i) H2SO4, 0 8C; (ii) Lutidine, CICOCH3, dry CH2Cl2, 0 8C; (iii) Br2, dry CH2Cl2; (iv) m-CPBA, CH2Cl2, 0 8C; (v) Py,
CICO(CH2)10CH3, dry CH2Cl2, 0 8C.
Bignoniaceae family.15 They are also commercial products
easily available. The furan (nZ0) and pyran (nZ1) ortho-
1,2-naphthoquinones were synthesized from 1 and 2.
Lapachol was converted into ortho-naphthoquinones by
intra-cyclization in different conditions15,16 (H2SO4, Br2,
m-CPBA). The treatment of 1 with m-CPBA also afforded
para-1,4-naphthoquinone analogues (a-isomers 8 and 9)
(see Scheme 2).
B and C, leading to the corresponding macrolactones
(Scheme 4).
The non-prenyl ortho-naphthoquinones 10 and 12 were
obtained from lawsone 2 following the reactions shown in
Scheme 3. The Knoevenagel condensation of 2 and
paraformaldehyde (CH2O)n leads to a quinone methide
intermediate, which undergoes hetero Diels–Alder reaction
with styrene as dienophile17 yielding, in one-pot reaction,
the pyran-naphthoquinone derivatives 10 and 11. The
treatment of 2 with CAN and styrene18 also yielded in
one-pot reaction the dihydrofuran-naphthoquinone deriva-
tives 12 and 13 via [3C2] type cycloaddition.
Scheme 4. Reagents and conditions: (i) 1,2-ethylenediamine or trans-1,2-
˚
diamine cyclohexane, molecular sieves 4 A toluene, D, 24 h–2 days; (ii) (a)
O3, K78 8C, dry CH2Cl2, 10–20 min. (b) Me2S.
This enol double bond shows a behaviour similar to the
9,10-double bond in polyaromatic phenanthrene systems,
which is the most labile in terms of its chemical reactivity,
and readily broken under oxidative conditions to yield
dialdehydes or acid derivatives.20
1,4-Diazaphenanthrene derivatives were synthesized by
condensation of the ortho-quinones with 1,2-ethylendia-
mine or trans-1,2-diaminecyclohexane.19
By far, the most general route to macrolactones is by
intramolecular ring closure.21 Other strategies are ring
contraction and ring expansion. Ring contractions leading to
macrolactones are relatively rare because of the problem of
finding suitable large ring precursors for reactions.22 The
ring expansion can be achieved by cleavage of a C–C bond
of suitable starting materials,23 by C]C double bond
cleavage of bicyclic vinyl ethers,24 and sometimes also by a
Baeyer-Villiger oxidation reaction.25
To the best of our knowledge, this letter presents the first
example of macrolide formation by ozonolysis of an
aromatic double bond at the site of fusion of the pyran or
dihydrofuran moiety.
Scheme 3. Reagents and conditions: (i) Dioxane, 7 equiv (CH2O)n, reflux,
3 equiv styrene; (ii) CH3CN/H2O (3/1), 2 equiv CAN, 0 8C-rt, 10 equiv
styrene.
Table 1 summarizes the results obtained in the formation
of 1,4-diazaphenanthrene derivatives and macrocyclic
compounds. The reactivity seemed quite substrate
dependent. The diazines from 1,2-ethylenediamine were
obtained in yields higher than those from trans-1,2-
The dihydrofuran or pyran 1,4-diazaphenanthrene com-
pounds were treated with ozone, which produced a selective
oxidative cleavage of the enol double bond shared by rings

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
439
Table 1. Yields of 1,4-diazaphenanthrenes (14–24) and macrolactones (25–35)
Entry
n
R
R1
R2
R3
macrolactones
25 68%
1,4-diazaphenanthrenes
1
2
3
4
5
6
7
8
0
0
1
1
1
1
0
1
1
1
1
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
–(CH2)4–
H
H
H
H
H
–C(OH)(CH3)2
Ph
Me
Me
Me
Me
H
H
H
H
H
OH
Br
14 70%
15 49%
16 71%
17 47%
18 51%
26 22%
27 68%
28 47%
29 46%
30 22%
31 70%
32 61%
33 68%
34 37%
35 53%
Me
Me
Me
Me
H
Me
Me
Me
H
–OCO(CH2)10CH3 19 78%
–C(OH)(CH3)2
H
H
OH
Br
H
20 70%
21 68%
22 89%
23 80%
24 51%
Me
Me
Me
Ph
9
10
11
diaminecyclohexane. The best results in the ozonolysis were
found for 1,4-diazaphenanthrene derivatives bearing non-
voluminous substituents at the pyran or dihydrofuran ring
(compounds 25, 27, 31 and 32).
of conformers I and II are similar to the geometries defined
as S5 and S9 respectively, with slight distortions due to the
presence of aromatics rings.
The values of coupling constants between the proton
geminal to the bromine group and the contiguous hydrogens
were estimated, and the results agree with the experimental
data.
We also tried an oxidative cleavage using m-CPBA as
oxidative agent, but mixtures of several N-oxide derivatives
and polyalcohols were obtained. However, the ozonolysis
process provides cleaner and more selective reactions, only
in one case (Entry 9), was the polyalcohol 36 (21%)
produced together with the desired macrolactone 33.
Macrolides are very important target molecules in synthetic
studies because of their biological and medicinal activities.
Our work describes a new pathway to form highly
functionalized 9- and 10-membered lactone rings from
phenanthrenic aromatic systems linked face-to-face in a
heterocyclic system.
Studies concerning the evaluation of biological activities,
and the extended application of this methodology to other
phenanthrenic systems, are in progress.
The NMR spectra of the 10-membered macrolactones (nZ
1) with R3ZBr, –OH or –OCO(CH2)10CH3 (compounds 28,
29, 30, 33 and 34), showed the existence of two
thermodynamically interchangeable conformers in a ratio
3:1. When R3ZBr (27 and 32), the two conformers are easy
to distinguish in their 1H and 13C NMR spectra. In order to
obtain an approximate idea on the geometry and energy of
these molecules, an analysis was made using GMMX
calculations.26 After multiple minimizations of 32, two
main lower-energy conformers I and II were found (see
Fig. 1). According to the studies on C7–C10 cycloalkanes
conformers recently carried out by Wiberg,27 the structures
3. Experimental
3.1. General methods
All condensation reactions of the ortho-quinones with 1,2-
diamine were carried out in toluene using activated
˚
molecular sieves 4 A. Ozonolysis reactions were carried
out on anhydrous conditions using glassware dried over-
night at 100 8C and flamed just before using it. CH2Cl2 was
dried on CaH2 and distilled before use. Me2S was dried on
CaH2 and distilled over molecular sieves. Ozon-Generator
OZIV Fisher Labortechnik was used to generate O3 flow.
Reactions were monitored by TLC (on silica gel
POLYGRAMw SIL G/UV254 foils). Purification by column
flash-chromatography used Merck Kiesel 60-H (0.063–
0.2 mm) as adsorbent and different mixtures of hexanes–
ethylacetate as eluent. Pre-coated TLC plates SIL G-100
UV254 (Macherey-Nagel) were used for preparative-TLC
purification. H and 13C NMR spectra were recorded in
1
CDCl3 or C6D6 using a Bruker AMX-300 MHz. Chemical
Figure 1. Lower-energy Conformers I and II.

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
440
shifts are given in parts per million (ppm) and J values are
given in Hertz (Hz). Complete 1H and 13C assignments were
achieved by 2D NMR spectroscopy (COSY, HMBC and
HSQC). Bidimensional spectra were recorded in CDCl3 or
C6D6 using a Bruker AMX-400 MHz. MS and HRMS were
recorded at VG Micromass ZAB-2F. All compounds were
named using ACD40 Name-Pro program, which is based on
IUPAC rules.
general procedure described above, 219 mg (0.90 mmol)
of 3 were treated with 230 mL (1.92 mmol) of trans-1,2-
diaminecyclohexane. The crude was purified by flash
chromatography on silica gel using Hex/EtOAc (9:1) as
1
eluent, to obtain 204 mg (71%) of 16. H NMR (C6D6) d:
9.57 (1H, m, H-8), 8.55 (1H, m, H-5), 7.53 (2H, m, H-6C
H-7), 3.32 (2H, t, JZ6.7 Hz, H-1), 3.06 (4H, m, H-10C
H-13), 1.66 (2H, t, JZ6.7 Hz, H-2), 1.61 (4H, m, H-11C
H-12), 1.26 (6H, s, H-10CH-20). 13C NMR (C6D6) d: 151.9
(s, C-9a), 149.7 (s, C-4a), 148.4 (s, C-13a), 141.3 (s, C-14a),
135.9 (s, C-8b), 131.0 (s, C-8a), 128.1 (s, C-4b), 127.9 (d,
C-6), 126.9 (d, C-7), 124.5 (d, C-8), 122.0 (d, C-5), 110.3 (s,
C-14b), 74.9 (s, C-3), 33.0 (t, C-2), 32.60(t, C-10 or 13), 32.3
(t, C-13 or 10), 26.4!2 (q, C-10CC-2 ), 23.0!2 (t, C-11,
12), 18.3 (t, C-1). MS m/z (rel. int): 318 (MC, 83), 303
(MCKMe, 6), 275 (MCKC3H7, 100). HRMS: 318.1723
(calcd for C21H22 N2O (MC) 318.1732).
3.2. General procedure for the preparation of 1,4-
diazaphenantrenes (14–24)
A solution of ortho-naphthoquinone and trans-1,2-diamine-
cyclohexane or 1,2-ethylendiamine (1.2–2 equiv) in dry
toluene was stirred under reflux for 24 h in the presence of
˚
molecular sieves 4 A. The reaction mixture was cooled to
room temperature, filtered and the solvent removed under
vacuum. The crude product was chromatographed using
mixtures of hexanes/EtOAc as eluent.
3.2.4. 3,3-Dimethyl-2,3,10,11,12,13-hexahydro-1H-
benzo[a]pyrano[2,3-c]phenazin-2-ol (17). Following the
general procedure described above, 180 mg (0.70 mmol) of
6 were treated with 100 mL (0.83 mmol) of trans-1,2-
diaminecyclohexane. The crude was chromatographed on
silica gel with 9:1 to 1:1 Hex/EtOAc, to obtain 108 mg
3.2.1. 2-(1,2,9,10,11,12-Hexahydrobenzo[a]furo[2,3-c]
phenazin-2-yl)-2-propanol (14). Following the general
procedure described above, 30 mg (0.12 mmol) of 5 were
treated with 17 mL (0.14 mmol) of trans-1,2-diaminecyclo-
hexane. The crude was chromatographed on silica gel with
1
(49%) of 17. H NMR (CDCl3) d: 9.01 (1H, m, H-8), 8.21
1
(1H, m, H-5), 7.66 (2H, m, H-6CH-7), 4.02 (1H, bs, H-2),
3.32 (2H, m, H-1), 3.27–3.10 (2H, m, H-13), 3.04 (2H, m,
H-10), 2.46 (1H, bs, OH), 2.03 (4H, m, H-11CH-12), 1.58
(3H, s, H-10), 1.39 (3H, s, H-20). 13C NMR (CDCl3) d: 152.2
(s, C-9a), 149.0 (s, C-13a), 148.4 (s, C-4a), 140.7 (s, C-14a),
135.5 (s, C-8b), 130.1 (s, C-8a), 127.7 (d, C-7), 127.1 (d,
C-6), 126.9 (s, C-4b), 123.9 (d, C-8), 121.6 (d, C-5), 107.6
(s, C-14b), 78.0 (s, C-3), 69.5 (d, C-2), 32.9 (t, C-13), 32.6
(t, C-10), 27.5 (t, C-1), 24.4 (q, C-10), 23.0!2 (t, C-11C
C-12), 22.6 (q, C-20). MS m/z (rel. int): 334 (MC, 36), 263
(MCKC(CH3)2CHOH, 100). HRMS: 334.1674 (calcd for
C21H22 N2O2 (MC) 334.1681).
9:1 to 1:1 Hex/EtOAc, to obtain 27 mg (70%) of 14. H
NMR (CDCl3) d: 9.15 (1H, m, H-7), 8.04 (1H, m, H-4), 7.71
(2H, m, H-5CH-6), 4.99 (1H, m, H-2), 3.66 (1H, dd, JZ
15.8, 9.9 Hz, H-1a), 3.58 (1H, dd, JZ15.8, 8.8 Hz, H-1b),
3.17 (4H, m, H-9CH-12), 2.04 (4H, m, H-10CH-11), 1.46
(3H, s, H-20), 1.31 (3H, s, H-30). 13C NMR (CDCl3) d: 155.8
(s, C-3a), 152.9 (s, C-8a), 148.7 (s, C-12a), 139.2 (s, C-13a),
136.6 (s, C-7b), 131.3 (s, C-7a), 128.0 (d, C-5), 127.2 (d,
C-6), 124.8 (d, C-7), 122.5 (s, C-3b),0121.4 (d, C-4), 114.3
(s, C-13b), 91.1 (d, C-2), 72.2 (s, C-1 ), 32.9 (t, C-12), 32.8
(t, C-9), 29.9 (t, C-1), 26.0 (q, C-20), 23.8 (q, C-30), 23.0!2
(t, C-10, 11). MS m/z (rel. int): 334 (MC, 100), 275 (MCK
C(OH)(CH3)2, 78), 263 (MCK71, 97). HRMS: 334.1674
(calcd for C21H22 N2O2 (MC) 334.1681).
3.2.5. 2-Bromo-3,3-dimethyl-2, 3,10,11,12,13-hexahydro-
1H-benzo[a]pyrano[2,3-c]phenazines (18). Following the
general procedure described above, 97 mg (0.30 mmol) of 4
were treated with 43 mL (0.36 mmol) of trans-1,2-diamine-
cyclohexane. The crude was purified by flash chromato-
graphy on silica gel using Hex/EtOAc (19:1) as eluent, to
obtain 61 mg (51%) of 18. 1H NMR (CDCl3) d: 9.11 (1H, m,
H-8), 8.25 (1H, m, H-5), 7.68 (2H, m, H-6CH-7), 4.47 (1H,
dd, JZ8.5, 5.6 Hz, H-2), 3.92 (1H, dd, JZ18.0, 5.6 Hz,
H-1a), 3.61 (1H, dd, JZ18.0, 8.5 Hz, H-1b), 3.16 (4H, m,
H-13CH-10), 2.03 (4H, m, H-11CH-12), 1.70 (3H, s,
H-10), 1.58 (3H, s, H-20). 13C NMR (CDCl3) d: 152.4 (s,
C-9a), 149.2 (s, C-13a), 148.4 (s, C-4a), 140.1 (s, C-14a),
135.8 (s, C-8b), 130.4 (s, C-8a), 128.0 (d, C-6), 127.2 (d,
C-7), 127.0 (s, C-4b), 124.0 (d, C-8), 121.7 (d, C-5), 108.9
(s, C-14b), 77.9 (s, C-3), 53.0 (d, C-2), 32.9 (t, C-13), 32.7
(t, C-10), 30.3 (t, C-1), 26.8 (q, C-10), 23.1 (t, C-11), 23.0 (t,
C-12), 22.0 (q, C-20). MS m/z (rel. int): 398 (MCC2, 46),
396 (MC, 46), 317 (MCKBr, 100). HRMS: 396.0860
(calcd for C21H21 N2O Br79 (MC) 396.0837).
3.2.2. 2-Phenyl-1,2,9,10,11,12-hexahydrobenzo[a]furo
[2,3-c]phenazines (15). Following the general procedure
described above, 108 mg (0.39 mmol) of 12 were treated
with 88 mL (0.73 mmol) of trans-1,2-diaminecyclohexane.
The crude was chromatographed on silica with 19:1 to 4:1
Hex/EtOAc, to yield 67 mg (49%) of 15. 1H NMR (CDCl3)
d: 9.18 (1H, m, H-7), 8.13 (1H0, m, H-4), 7.71 (2H,0m, H-5C
H-6), 7.50 (2H, m, H-20CH-6 ), 7.34 (3H, m, H-3 CH-40C
H-50), 6.15 (1H, m, H-2), 4.15 (1H, dd, JZ15.6, 10.1 Hz,
H-1a), 3.69 (1H, dd, JZ15.6, 7.4 Hz, H-1b), 3.19 (2H, bs,
H-9), 3.14 (2H, bs, H-12), 2.03 (4H, bs, H-10CH-11). 13C
NMR (CDCl3) d: 156.0 (s, C-3a), 152.9 (s, C-8a), 148.6 (s,
C-12a), 142.1 (s, C-10), 139.3 (s, C-13a), 136.7 (s, C-7b),
131.5 (s, C-7a), 128.7!2 (d, C-300, 500), 128.1!2 (d, C-5, 40),
127.2 (d, C-6), 125.7!2 (d, C-2 , 6 ), 124.8 (d, C-7), 122.7
(s, C-3b), 121.8 (d, C-4), 113.3 (s, C-13b), 85.6 (d, C-2),
37.3 (t, C-1), 32.9 (t, C-12), 32.8 (t, C-9), 23.1 (t, C-11), 23.0
(t, C-10). MS m/z (rel. int): 352 (MC, 100), 275 (MCKPh,
69). HRMS: 352.1596 (calcd for C24H20 N2O (MC)
352.1576).
3.2.6. 3,3-Dimethyl-2,3,10,11,12,13-hexahydro-1H-ben-
zo[a]pyrano[2,3-c]phenazin-2-yl laurate (19). Following
the general procedure described above, 98 mg (0.22 mmol)
of 7 were treated with 52 mL (0.43 mmol) of trans-1,2-
3.2.3. 3,3-Dimethyl-2,3,10,11,12,13-hexahydro-1H-
benzo[a]pyrano[2,3-c]phenazines (16). Following the

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
441
diaminecyclohexane. The crude was chromatographed on
silica gel with 19:1 to 4:1 Hex/EtOAc, to obtain 88 mg
(78%) of 19. H NMR (CDCl3) d: 9.12 (1H, m, H-8), 8.30
NMR (CDCl3) d: 9.12 (1H, m, H-12), 8.76 (1H, bs, H-3),
8.72 (1H, bs, H-2), 8.33 (1H, m, H-9), 7.73 (2H, m, H-10C
H-11), 5.11 (1H, m, H-6), 3.46 (1H, dd, JZ17.7, 5.0 Hz,
H-5a), 3.31 (1H, dd, JZ17.7, 4.5 Hz, H-5b), 1.57 (3H, s,
H-10), 1.47 (3H, s, H-20). 13C NMR (CDCl3) d: 149.8 (s,
C-8a), 143.5 (d, C-3), 140.3 (d, C-2), 138.7 (s, C-4a), 134.7
(s, C-12b), 130.4 (s, C-12a), 128.8 (d, C-10), 127.6 (d,
C-11), 127.5 (s, C-8b), 124.2 (d, C-12), 122.0 (d, C-9),
108.0 (s, C-4b), 78.3 (s, C-7), 69,4 (d, C-6), 27.5 (t, C-5),
24.7 (q, C-10), 22.2 (q, C-20). MS m/z (rel. int): 280 (MC,
41), 209 (MCK71, 100). HRMS: 280.1197 (calcd for
C17H16 N2O (MC) 280.1212).
1
(1H, m, H-5), 7.68 (2H, m, H-6CH-7), 5.28 (1H, t, JZ
5.2 Hz, H-2), 3.51 (1H, dd, JZ18.1, 5.3 Hz, H-1a), 3.27 (dd,
1H, JZ18.1, 5.2 Hz, H-1b), 03.18 (2H, bs, H-13), 3.13 (2H,
bs, H-10), 2.30 (2H, m, H-4 ), 2.02 (4H, m,0 H-11CH-12),
1.57 (4H, m, H-50CH-60), 1.48 (3H, s,0H-2 ), 1.46 (3H, s,
H-10), 1.21 (14H, bs, H-70CH-80CH-9 CH-100CH-110C
H-120CH-1300), 0.87 (3H, m, H-140). 13C NMR (CDCl3) d:
173.3 (s, C-3 ), 152.3 (s, C-9a), 149.0 (s, C-13a), 148.5 (s,
C-4a), 140.7 (s, C-14a), 135.8 (s, C-8b), 130.4 (s, C-8a),
127.9 (d, C-7), 127.2 (d, C-6), 127.1 (s, C-4b), 124.0 (d,
C-8), 121.8 (d, C-5), 107.7 (s, C-14b), 76.2 (s, C-3), 70.7 (d,
C-2), 34.5 (t), 32.9 (t), 32.7 (t), 31.9 (t), 29.5!2 (t), 29.4 (t),
29.3 (t), 29.2 (t), 29.1 (t), 25.1 (t), 24.8 (q, C-10), 24.7 (t),
23.1 (t, C-12), 23.0 (t, C-11), 22.6 (t), 22.6 (q, C-20), 14.1 (q,
C-140). MS m/z (rel. int): 516 (MC, 8), 316 (MCK
OCO(CH2)10CH3, 61), 301 (316-Me, 100). HRMS:
516.3351 (calcd for C33H44N2O3 (MC) 516.3352).
3.2.10. 6-Bromo-7,7-dimethyl-6,7-dihydro-5H-benzo[ f]
pyrano[2,3-h]quinoxaline (23). Following the general
procedure described above, 108 mg (0.33 mmol) of 4 were
treated with 45 mL (0.67 mmol) of 1,2-ethylendiamine. The
crude was purified by flash chromatography on silica gel
using Hex/EtOAc (9:1) as eluent, to obtain 88 mg (80%) of
1
23. H RMN (CDCl3) d: 9.15 (1H, m, H-12), 8.81 (1H, d,
JZ1.9 Hz, H-3), 8.76 (1H, d, JZ1.9 Hz, H-2), 8.32 (1H, m,
H-9), 7.76 (2H, m, H-10CH-11), 4.49 (1H, dd, JZ8.4,
5.6 Hz, H-6), 3.94 (1H, dd, JZ17.9, 5.6 Hz, H-5a), 3.65
(1H, dd, JZ17.9, 8.4 Hz, H-5b), 1.71 (3H, s, H-10), 1.60
(3H, s, H-20). 13C RMN (CDCl3) d: 149.7 (s, C-8a), 143.6 (d,
C-3), 142.5 (s, C-4a), 140.5 (d, C-2), 138.4 (s, C-12b), 130.5
(s, C-12a), 128.9 (d, C-10), 127.8 (d, C-11), 127.5 (s, C-8a),
124.3 (d, C-12), 121.9 (d, C-9), 109.0 (s, C-4b), 78.3 (s,
C-7), 52.4 (d, C-6), 30.3 (t, C-5), 26.7 (q, C-10), 22.3 (q,
C-20). MS m/z (rel. int): 398 (MCC2, 46), 396 (MC, 46),
317 (MCKBr, 100). HRMS: 396.0860 (calcd for C21H21
N2O Br79 (MC) 396.0837).
3.2.7. 2-(2,3-Dihydrobenzo[f]furo[2,3-h]quinoxalin-2-
yl)-2-propanol (20). Following the general procedure
described above, 101 mg (0.39 mmol) of 5 were treated
with 52 mL (0.78 mmol) of 1,2-ethylendiamine. The crude
was chromatographed on silica gel with 4:1 to 2:3 Hex/
1
EtOAc, to obtain 79 mg (70%) of 20. H NMR (CDCl3) d:
9.09 (1H, m, H-8), 8.72 (1H, d, JZ2.1 Hz, H-5), 8.67 (1H,
d, JZ2.1 Hz, H-6), 7.98 (1H, m, H-11), 7.67 (2H, m, H-9C
H-10), 4.98 (1H, t, JZ9.3 Hz, H-2), 3.60 (2H, d, JZ9.3 Hz,
H-3), 1.47 (3H, s, H-20), 1.31 (3H, s, H-30). 13C NMR
(CDCl3) d: 157.0 (s, C-11b), 143.9 (d, C-5), 141.4 (s, C-3b),
139.7 (d, C-6), 138.9 (s, C-8b), 131.3 (s, C-8a), 128.7 (d,
C-10), 127.6 (d, C-9), 125.0 (d, C-8), 122.8 (s, C-11a), 121.5
(d, C-11), 114.5 (s, C-4b), 91.5 (d, C-2), 72.0 (s, C-10), 29.5
(t, C-3), 26.0 (q, C-20), 24.0 (q, C-30). MS m/z (%): 280
(MC, 41), 221 (MCK71, 100). HRMS: 280.1210 (calcd for
C17H16 N2O2 (MC) 280.1212).
3.2.11. 7-(1-Hydroxy-1-methylethyl)-6,7-dihydro[2] ben-
zoxonino[6,7-b]pyrazine-5,9-dione (24). Following the
general procedure described above, 43 mg (0.15 mmol) of
4 were treated with 20 mL (0.30 mmol) of 1,2-ethyl-
endiamine. The crude was purified by flash chromatography
on silica gel using Hex/EtOAc (9:1) as eluent, to obtain
3.2.8. 7,7-Dimethyl-6,7-dihydro-5H-benzo[f]pyrano [2,3-
h]quinoxaline (21). Following the general procedure
described above, 110 mg (0.45 mmol) of 3 were treated
with 60 mL (0.90 mmol) of 1,2-ethylendiamine. The crude
was chromatographed on silica gel with 19:1 to 4:1 Hex/
1
22 mg (51%) of 24. H RMN (CDCl3) d: 9.16 (1H, m,
H-12), 8.81 (1H, d, JZ2.0 Hz, H-3), 8.75 (1H, d, JZ2.0 Hz,
H-2), 8.37 (01H, m,0 H-9), 7.74 (2H, m0, H-10CH-11), 7.55
(2H, m, H-2 CH-6 ), 7.44 (3H, m, H-3 CH-40CH-50), 5.34
(1H, d, JZ10.1 Hz, H-7), 3.43 (1H, m, H-6a), 3.24 (1H, m,
H-6b), 2.52 (1H, m, H-5a), 2.25 (1H, m, H-5b). 13C NMR
(CDCl3) d: 151.8 (s, C-8a), 143.5 (d, C-3), 143.2 (d, C-4a),
141.1 (s, C-10), 140.3 (d, C-2), 138.3 (s,0 C-12b), 130.3 (s,
C-12a), 128.8 (d, C-10), 128.6!2 (d, C-3 CC-50), 127.90(d,
C-400), 127.6 (s, C-8b), 127.5 (d, C-11), 125.9!2 (d, C-2 C
C-6 ), 124.3 (d, C-12), 121.8 (d, C-9), 111.5 (s, C-4b), 78.3
(s, C-7), 29.5 (t, C-6), 20.5 (t, C-5). MS m/z (rel. int): 312
(MC, 62), 221 (MCKN–Ph, 100). HRMS: 312.1282 (calcd
for C21H16 N2O (MC) 312.1263).
1
EtOAc, to obtain 81 mg (68%) of 21. H NMR (CDCl3) d:
9.13 (1H, m, H-12), 8.80 (1H, d, JZ2.0 Hz, H-3), 8.71 (1H,
d, JZ2.0 Hz, H-2), 8.33 (1H, m, H-9), 7.73 (2H, m, H-10C
H-11), 3.23 (2H, t, JZ6.7 Hz, H-5), 2.03 (2H, t, JZ6.7 Hz,
H-6), 1.50 (6H, s, H-10CH-20). 13C NMR (CDCl3) d: 150.8
(s, C-8a), 143.4 (s, C-4a), 143.4 (d, C-3), 139.9 (d, C-2),
138.1 (s, C-12b), 130.3 (s, C-12a), 128.6 (d, C-10), 128.2 (s,
C-8b), 127.3 (d, C-11), 124.2 (d, C-12), 121.9 (d, C-9),
110.0 (s, C-4b), 75.7 (s, C-7), 32.4 (t, C-6), 26.7!2 (q,
C-10CC-20), 18.2 (t, C-5). MS m/z (rel. int): 264 (MC, 65),
249 (MCKMe, 16), 221 (MCKMe–CO, 100). HRMS:
264.1249 (calcd for C17H16 N2O (MC) 264.1263).
3.3. General procedure for the preparation of the
macrolactones (25–35)
3.2.9. 7,7-Dimethyl-6,7-dihydro-5H-benzo[f]pyrano [2,3-
h]quinoxalin-6-ol (22). Following the general procedure
described above, 152 mg (0.59 mmol) of 6 were treated with
80 mL (1.20 mmol) of 1,2-ethylendiamine. The crude was
purified by flash chromatography on silica gel using Hex/
A solution of diazine in dry CH2Cl2 cooled to K78 8C, was
ozonized until the colour of the solution changed to dark
blue-grey. The reaction mixture was then quenched with dry
Me2S (2 equiv), concentrated under vacuum and chromato-
graphed by preparative-TLC using mixtures of hexanes/
1
EtOAc (3:2) as eluent, to obtain 147 mg (89%) of 22. H

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
442
EtOAc as eluent, to afford the corresponding macrolactones
25–35.
Me2S and chromatographed by preparative-TLC using Hex/
EtOAc (7:3) as eluent, to obtain 17 mg (47%) of 28. Major
1
conformer: H NMR (CDCl3) d: 8.00 (1H, m, H-4), 7.64
(1H, m, H-1), 7.47 (2H, m, H-2CH-3), 4.02–3.96 (2H, m,
H-8CH-9a), 3.02 (4H, bs, H-12CH-15), 2.73 (1H, m,
H-9b), 2.30 (1H, bd, JZ5.6 Hz, OH), 2.00 (4H, bs, H-13C
H-14), 1.61 (3H, s, H-10), 1.52 (3H, s, H-20). 13C NMR
(CDCl3) d: 197.0 (s, C-10), 171.4 (s, C-5), 154.6 (s, C-15a),
153.4 (s, C-16b), 152.5 (s, C-11a), 149.5 (s, C-10a), 135.4
(s, C-16a), 132.8 (d, C-3), 132.0 (d, C-2), 130.9 (s, C-4a),
128.6 (d, C-4), 124.8 (d, C-1), 78.6 (s, C-7), 70.2 (d, C-8),
44.5 (t, C-9), 32.1 (t, C-12 0or C-15), 31.4 (t, C-15 or C-12),
27.4 (q, C-10), 24.4 (q, C-2 ), 22.5 (t, C-13 or C-14), 22.4 (t,
C-14 or C-13). Minor conformer: 1H NMR (CDCl3) d: 8.00
(1H, m, H-4), 7.64 (1H, m, H-1), 7.47 (2H, m, H-2CH-3),
4.34 (1H, bs, H-9a), 3.92 (1H, m, H-8), 3.02 (4H, bs, H-12C
H-15), 2.88 (1H, m, H-9b), 2.61 (1H, bd, JZ4.8 Hz, OH),
2.00 (4H, bs, H-13CH-14), 1.67 (3H, s, H-10), 1.31 (3H, s,
H-20). MS m/z (rel. int): 366 (MC, 4), 350 (MCKMe, 2),
295 (MCK71, 100). HRMS: 366.7127 (calcd for C21H22
N2O4 (MC) 350.7101).
3.3.1. 7-(1-Hydroxy-1-methylethyl)-7,8,11,12,13,14-
hexahydro[2]benzoxonino[6,7-b]quinoxaline-5,9-dione
(25). 16 mg (0.05 mmol) of 14 in 8 mL of dry CH2Cl2 were
ozonized following the general procedure described above.
The crude was quenched with 6 mL of dry Me2S and
chromatographed by preparative-TLC using Hex/EtOAc
1
(7:3) as eluent, to obtain 12 mg (68%) of 25. H RMN
(CDCl3) d: 8.03 (1H, m, H-4), 7.92 (1H, m, H-1), 7.72 (1H,
m, H-3), 7.52 (1H, m, H-2), 5.49 (1H, bs, H-7), 4.12 (2H, m,
H-8), 3.05 (4H, bs, H-11CH-14), 2.000(4H, bs, H-12CH-
13), 1.19 (3H, s, H-20), 1.16 (3H, s, H-3 ). MS m/z (rel. int):
366 (MC, 2), 348 (MCKH2O, 3), 289 (348-C(OH)(CH3)2,
100). HRMS: 366.1548 (calcd for C21H22 N2O4 (MC)
366.1579).
3.3.2. 7-Phenyl-7,8,11,12,13,14-hexahydro[2] benzoxo-
nino[6,7-b]quinoxaline-5,9-dione
(26).
48 mg
(0.13 mmol) of 15 in 10 mL of dry CH2Cl2 were ozonized
following the general procedure described above. The crude
was quenched with 15 mL of dry Me2S and chromato-
graphed by preparative-TLC using Hex/EtOAc (7:3) as
3.3.5.
8-Bromo-7,7-dimethyl-8,9,12,13,14,15-hexa-
hydro-5H-[2]benzoxecino[7,8-b]quinoxaline-5,10(7H)-
dione (29). 20 mg (0.05 mmol) of 18 in 8 mL of dry CH2Cl2
were ozonized following the general procedure described
above. The crude was quenched with 6 mL of dry Me2S and
chromatographed by preparative-TLC using Hex/EtOAc
(4:1) as eluent, to obtain 10 mg (46%) of 29. Major
1
eluent, to obtain 11 mg (22%) of 26. H RMN (CDCl3) d:
8.02 (1H, bs, H-1), 7.90 (1H, d, JZ7.8 Hz, H-4), 7.67 (1H, t,
JZ7.5 Hz,0H-2), 7.49 (1H, t, JZ7.5 Hz, H-3), 07.25 (3H, m,
H-30CH-4 CH-50), 7.06 (2H, bs, H-20CH-6 ), 6.49 (1H,
bs, H-7), 3.95 (1H, bs, H-8a), 3.52 (1H, bs, H-8b), 3.01 (4H,
m, H-11CH-14), 1.92 (4H, s, H-12CH-13). MS m/z (rel.
int): 384 (MC, 1), 340 (MCKCO2, 9), 252 (MCK
COCH2CHPh, 100). HRMS: 384.1466 (calcd for C24H20
N2O3 (MC) 384.1474).
1
conformer: H RMN (CDCl3) d: 8.07 (1H, d, JZ7.5 Hz,
H-4), 7.66 (1H, m, H-1), 7.50 (2H, m, H-2CH-3), 4.32 (1H,
dd, JZ12.5, 4.1 Hz, H-8), 4.10 (1H, dd, JZ14.4, 4.2 Hz,
H-9a), 3.10 (1H, m, H-9b), 3.03 (4H, m, H-12CH-15), 2.02
(4H, m, H-13CH-14), 1.74 (3H, s, H-10), 1.69 (3H, s, H-20).
13C NMR (CDCl3) d: 197.6 (s, C-10), 164.3 (s, C-5), 153.7
(s, C-15a), 149.9 (s, C-16b), 149.8 (s, C-11a), 148.0 (s,
C-10a), 138.1 (s, C-16a), 133.1 (d, C-2 or C-3), 132.9 (d,
C-2 or C-3), 131.3 (d, C-4), 130.9 (s, C-4a), 128.7 (d, C-1),
87.1 (s, C-7), 52.6 (d, C-8), 47.2 (t, C-9), 32.1 (t, C-12 or
C-15), 31.5 (t, C-12 or C-15), 25.4 (q, C-10), 22.5!2 (t,
3.3.3. 7,7-Dimethyl-8,9,12,13,14,15-hexahydro-5H-
[2]benzoxecino[7,8-b]quinoxaline-5,10(7H)-dione (27).
97 mg (0.30 mmol) of 16 in 10 mL of dry CH2Cl2 were
ozonized following the general procedure described above.
The crude was quenched with 40 mL of dry Me2S and
chromatographed by preparative-TLC using Hex/EtOAc
1
1
C-13CC-14), 18.3 (q, C-20). Minor conformer. H RMN
(4:1) as eluent, to obtain 71 mg (68%) of 27. H NMR
(CDCl3) d: 7.91 (1H, d, JZ7.8 Hz, H-4), 7.70 (1H, m, H-1),
7.53 (2H, m, H-2CH-3), 5.22 (1H, dd, JZ12.6, 4.6 Hz,
H-8), 4.71 (1H, m, H-9a), 3.03 (5H, m, H-9bCH-12C
H-15), 2.00 (4H, m, H-13CH-14), 1.86 (3H, s, H-10), 1.16
(3H, s, H-20). MS m/z (rel. int): 430 (MCC2, 3), 428 (MC,
3), 349 (MCKBr, 4), 253 (MCKCO(CH2)CH(Br)C(Me)2,
100). HRMS: 428.0722 (calcd for C21H21N2O3Br79 (MC)
428.0736).
(C6D6) d: 8.22 (1H, d, JZ7.8 Hz, H-4), 7.68 (1H, d, JZ
7.8 Hz, H-1), 7.23 (1H, m, H-2), 7.02 (1H, m, H-3), 3.78
(1H, ddd, JZ13.8, 6.3, 4.2 Hz, H-9a), 2.74 (4H, m, H-12C
H-15), 2.59 (1H, ddd, JZ15.1, 11.2, 3.9 Hz, H-9b), 2.16
(1H, ddd, JZ14.8, 11.2, 4.2 Hz, H-8b), 1.66 (1H, ddd, JZ
18.7, 16.5, 5.8 Hz, H-7a), 1.44 (3H, s, H-10), 1.42 (m, 4H,
H-13CH-14), 1.16 (3H, s, H-20). 13C NMR (C6D6) d: 201.6
(s, C-10), 165.5 (s, C-5), 152.9 (s, C-15a), 150.4 (s, C-16b),
149.1 (s, C-11a), 148.4 (s, C-10a), 139.0 (s, C-16a), 133.4
(d, C-3), 132.0 (d, C-2), 130.6 (d, C-4), 129.2 (s, C-4a),
128.6 (d, C-1), 83.8 (s, C-7), 37.9 (t, C-8), 36.1 (t, C-9), 31.9
(t, C-12 or C-15), 31.4 (t, C-15 or C-12), 26.6 (q, C-10), 23.8
(q, C-20), 22.4 (t, C-13 or C-14), 22.3 (t, C-14 or C-13). MS
m/z (rel. int): 350 (MC, 4), 335 (MCKMe, 2), 253 (MCK
CO(CH2)C(Me)2, 100). HRMS: 350.1657 (calcd for C21H22
N2O3 (MC) 350.1630).
3.3.6. 7,7-Dimethyl-5,10-dioxo-7,8,9,10,12,13,14,15-octa-
hydro-5H-[2]benzoxecino[7,8-b]quinoxalin-8-yl laurate
(30). 54 mg (0.10 mmol) of 19 in 10 mL of dry CH2Cl2
were ozonized following the general procedure described
above. The crude was quenched with 13 mL of dry Me2S and
chromatographed by preparative-TLC using Hex/EtOAc
(4:1) as eluent, to obtain 18 mg (22%) of 30. Major
conformer: 1H NMR (C6D6) d: 8.44 (1H, d, JZ7.9 Hz,
H-4), 7.72 (1H, d, JZ7.9 Hz, H-1), 7.34 (1H, m, H-2), 7.13
(1H, m, H-3), 5.74 (1H, dd, JZ11.4, 4.6 Hz, H-8), 4.29 (1H,
dd, JZ13.4, 4.6 Hz, H-9a), 2.93 (1H, dd, JZ13.4, 11.4 Hz,
H-9b), 2.78 (4H, m, H-12CH-15), 2.10 (2H, m, H-13C
H-14), 1.77 (3H, s, H-10), 1.60 (3H, s, H-20), 1.49 (3H, s,
3.3.4. 8-Hydroxy-7,7-dimethyl-8,9,12,13,14,15-hexa-
hydro-5H-[2]benzoxecino[7,8-b]quinoxaline-5,10 (7H)-
dione (28). 33 mg (0.10 mmol) of 17 in 10 mL of dry
CH2Cl2 were ozonized following the general procedure
described above. The crude was quenched with 12 mL of dry

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
443
H-140), 1.37 (18H, m, H-50CH-60CH-70CH-80CH-90C
H-100CH-110CH-120CH-130), 1.01 (s, 3H, H-20). 13C
NMR (C6D6) d: 196.9 (s, C-10), 171.5 (s, C-5), 164.3 (s, C-
10), 153.5 (s, C-15a), 150.2 (s, C-16b), 149.5 (s, C-11a),
148.9 (s, C-10a), 139.4 (s, C-16a), 133.8 (d, C-3), 132.6 (d,
C-2), 132.4 (s, C-4a), 131.2 (d, C-4), 128.5 (d, C-1), 84.8 (s,
C-7), 72.8 (d, C-8), 42.5 (t, C-40), 34.0 (t), 32.0!2 (t), 31.9
(t), 31.3 (t), 29.9 (t),029.7 (t), 29.6 (t), 29.5 (t), 29.3!2 (t),
24.9 (t), 23.8 (q, C-1 ), 22.5 (t), 22.2 (t), 18.6 (q, C-20), 14.1
(q, C-140). MS m/z (rel. int): 549 (MCC1, 41), 349 (MCC
1-OCO(CH2)10CH3, 23), 253 (349-CO(CH2)2C(Me)2, 7), 69
(100). HRMS: 549.3341 (calcd for C33H45N2O5 (MCC1)
549.3328).
JZ5.8 Hz, OH), 1.62 (3H, s, H-10), 1.51 (3H, s, H-20). 13C
NMR (CDCl3) d: 196.7 (s, C-10), 175.4 (s, C-5), 150.6 (s,
C-14a), 150.6 (s, C-4a), 144.7 (d, C-3), 140.9 (d, C-2), 134.6
(s, C-14b), 132.9!2 (d, C-12CC-13), 131.0 (d, C-11),
129.3 (s, C-10a), 129.1 (d, C-14), 86.6 (s, C-8), 74.1 (d,
C-7), 44.6 (t, C-6), 24.4 (q, C-10), 24.1 (q, C-20). Minor
1
conformer: H NMR (CDCl3) d: 8.77 (d, JZ2.3 Hz, 1H,
H-2), 8.51 (m, 1H, H-3), 8.03 (m, 1H, H-11), 7.67 (m, 1H,
H-14), 7.52 (m, 2H, H-12, 13), 4.50 (m, 1H, H-7), 4.04
(m, 1H, H-6a), 2.89 (dd, JZ12.9, 4.6 Hz, 1H, H-6b), 2.36
(bd, JZ4.1 Hz, 1H, OH), 1.70 (s, 3H, H-10), 1.16 (s, 3H,
H-20). MS m/z (rel. int): 312 (MC, 1), 297 (MCKMe, 2),
199 (MCKCOCH2CH(OH)C(CH3)2, 65), 183 (199-16,
100). HRMS: 312.1128 (calcd for C17H16N2O4 (MC)
312.1110).
3.3.7. 7-(1-Hydroxy-1-methylethyl)-6, 7-dihydro[2]
benzoxonino[6,7-b]pyrazine-5,9-dione (31). 37 mg
(0.13 mmol) of 20 in 10 mL of dry CH2Cl2 were ozonized
following the general procedure described above. The crude
was quenched with 20 mL of dry Me2S and chromato-
graphed by preparative-TLC using Hex/EtOAc (1:4) as
3.3.10. 5-(2, 3-Dihydroxy-3-methylbutyl)-5-hydroxy ben-
zo[ f]quinoxalin-6(5H)-one (36). 1H NMR (CDCl3) d: 8.57
(1H, d, JZ2.3 Hz, H-3), 8.52 (1H, d, JZ2.3 Hz, H-2), 8.46
(1H, d, JZ7.5 Hz, H-10), 8.00 (1H, m,0H-7), 7.60 (2H, m,
H-8CH-9), 4.44 (1H, d, JZ5.5 Hz, H-2 ), 3.35 (1H, dd, JZ
14.2, 5.5 Hz, H-1a0), 2.94 (1H, d, JZ14.2 Hz, H-1b0), 1.51
(6H, s, H-100CH-40). 13C NMR (CDCl3) d: 199.8 (s, C-6),
152.7 (s, C-10b), 151.0 (s, C-4a), 144.0 (d, C-3), 143.5 (d,
C-2), 132.1 (s, C-10a), 131.1 (d, C-8 or 9), 130.9 (d, C-8 or
9), 129.0 (s, C-6a), 127.5 (d, C-10), 125.6 (d, C-7), 84.0 (d,
C-20), 82.2 (s, C-5), 69.9 (s, C-30), 38.8 (t, C-10), 27.3 (q,
C-40), 22.7 (q, C-100). MS m/z (rel. int): 314 (MC, 15), 299
(MCKMe, 21), 221 (MCK93, 100). HRMS: 314.1285
(calcd for C17H18N2O4 (MC) 314.1267).
1
eluent, to obtain 28 mg (70%) of 31. H NMR (CDCl3) d:
8.74 (1H, d, JZ2.4 Hz, H-2), 8.50 (1H, d, JZ2.4 Hz, H-3),
8.19 (1H, bs, H-13), 7.92 (1H, d, JZ7.8 Hz, H-10), 7.72
(1H, m, H-12), 7.56 (1H, m, H-11), 5.53 (1H, bs, H-7), 2.86
(1H, bs, H-6a), 1.87 (1H, bs, H-6b), 1.15 (3H, s, H-10), 1.13
(3H, s, H-20). MS m/z (rel. int): 312 (MC, 1), 297 (MCK
Me, 5), 254 (MCKMe–CO2, 54), 183 (254-
CHCOH(CH3)2, 100). HRMS: 297.0863 (calcd for C16H13
N2O4 (MCKMe) 297.0875).
3.3.8. 8,8-Dimethyl-7,8-dihydro-6H-[2]benzoxecino [7,8-
b]pyrazine-5,10-dione (32). 58 mg (0.21 mmol) of 21 in
10 mL of dry CH2Cl2 were ozonized following the general
procedure described above. The crude was quenched with
27 mL of dry Me2S and chromatographed by preparative-
TLC using Hex/EtOAc (3:2) as eluent, to obtain 38 mg
3.3.11. 7-Bromo-8,8-dimethyl-7,8-dihydro-6H-[2] benz-
oxecino[7,8-b]pyrazine-5,10-dione
(34).
57 mg
(0.17 mmol) of 23 in 10 mL of dry CH2Cl2 were ozonized
following the general procedure described above. The crude
was quenched with 20 mL of dry Me2S and chromato-
graphed by preparative-TLC using Hex/EtOAc (7:3) as
1
(61%) of 32. H NMR (CDCl3) d: 8.70 (1H, m, H-2), 8.49
(1H, m, H-3), 8.04 (1H, m, H-11), 7.65 (1H, m, H-14), 7.51
(2H, m, H-12CH-13), 3.65 (1H, ddd, JZ14.5, 5.8, 4.1 Hz,
H-6a), 2.67 (1H, ddd, JZ16.5, 14.5, 3.9 Hz, H-6b), 2.18
(1H, ddd, JZ18.7, 4.1, 3.9 Hz, H-7b), 1.990 (1H, ddd, JZ
18.7, 16.5, 5.8 Hz, H-7a), 1.63 (3H, s, H-1 ), 1.39 (3H, s,
H-20). 13C NMR (CDCl3) d: 201.9 (s, C-5), 164.9 (s, C-10),
153.4 (s, C-14b), 151.6 (s, C-4a), 144.4 (d, C-2), 140.5 (d,
C-3), 137.9 (s, C-14a), 132.7!2 (d, C-12, 13), 130.8 (d,
C-11), 129.0 (d, C-14), 128.2 (s, C-10a), 84.4 (s, 0C-8), 38.3
(t, C-7), 36.3 (t, C-6), 26.9 (q, C-10), 23.7 (q, C-2 ). MS m/z
(rel. int): 296 (MC, 17), 268 (MCKCO, 9), 199 (MCK
CO–Me–NCH]CHN, 100). HRMS: 296.1164 (calcd for
C17H16N2O3 (MC) 296.1161).
1
eluent, to obtain 23 mg (37%) of 34. Major conformer: H
NMR (CDCl3) d: 8.74 (1H, m, H-2), 8.55 (1H, m, H-3), 8.10
(1H, d, JZ7.9 Hz, H-11), 7.73 (1H, m, H-14), 7.51 (2H, m,
H-12CH-13), 4.30 (1H, dd, JZ12.5, 4.0 Hz, H-7), 4.08
(1H, dd, JZ14.3, 4.0 Hz, H-6b), 3.13 (1H, dd, JZ14.3,
12.5 Hz, H-6b), 1.76 (3H, s, H-10), 1.66 (3H, s, H-20). 13C
NMR (CDCl3) d: 196.8 (s, C-5), 163.9 (s, C-10), 153.5 (s,
C-14b), 151.1 (s, C-4a), 144.8 (d, C-2), 141.0 (d, C-3), 137.7
(s, C-14a), 133.1 (d, C-12), 132.9 (d, C-13), 131.4 (d, C-11),
129.1 (d, C-14), 127.6 (s, C-10a), 87.3 (d, C-8), 52.3 (d,
C-7), 47.1 (t, C-6), 25.3 (q, C-10), 18.3 (q, C-20). Minor
conformer: 1H NMR (CDCl3) d: 8.79 (m, 1H, H-2), 8.56 (m,
1H, H-3), 7.97 (d, JZ7.8 Hz, 1H, H-11), 7.73 (m, 1H,
H-14), 7.51 (m, 2H, H-12CH-13), 5.25 (dd, JZ12.6,
4.6 Hz, 1H, H-7), 4.47 (dd, JZ12.6, 12.1 Hz, 1H, H-6a),
3.06 (dd, JZ12.1, 4.6 Hz, 1H, H-6b), 1.87 (s, 3H, H-10),
1.13 (s, 3H, H-10). 13C NMR (CDCl3) d: 197.7 (s, C-5),
163.8 (s, C-10), 153.5 (s, C-14b), 151.1 (s, C-4a), 145.5 (d,
C-2), 140.7 (d, C-3), 137.7 (s, C-14a), 133.0 (d, C-12), 132.9
(d, C-13), 131.1 (d, C-11), 129.5 (d, C-14), 119.9 (s, C-10a),
86.4 (d, C-8), 51.4 (d, C-7), 44.5 (t, C-6), 26.8 (q, C-10), 21.6
(q, C-20). MS m/z (rel. int): 376 (MCC2, 0.4), 374 (MC,
0.4), 295 (MCKBr, 7), 199 (MCKCO(CH2)-
CH(Br)C(Me)2, 100). HRMS: 374.0350 (calcd for
C17H15N2O3Br79 (MC) 374.0266).
3.3.9. 7-Hydroxy-8,8-dimethyl-7,8-dihydro-6H-[2] benz-
oxecino[7,8-b]pyrazine-5, 10-dione (33). 21 mg
(0.08 mmol) of 22 in 10 mL of dry CH2Cl2 were ozonized
following the general procedure described above. The crude
was quenched with 10 mL of dry Me2S and chromato-
graphed by preparative-TLC using Hex/EtOAc (7:3) as
eluent, to obtain 16 mg (68%) of 33 and 5 mg (21%) of 36.
1
Major conformer: H NMR (CDCl3) d: 8.77 (1H, d, JZ
2.3 Hz, H-2), 8.51 (1H, d, JZ2.3 Hz, H-3), 8.05 (1H, d, JZ
7.8 Hz, H-11), 7.67 (1H, m, H-14), 7.52 (2H, m, H-12C
H-13), 4.12 (1H, m, H-7), 3.90 (1H, dd, JZ13.9, 4.4 Hz,
H-6a), 2.79 (1H, dd, JZ13.9, 10.3 Hz, H-6b), 2.26 (1H, bd,

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
444
9. Keller, T.; Neeland, E.; Retting, S.; Trotter, J.; Weiler, L.
J. Am. Chem. Soc. 1988, 110, 7858–7868. (b) Rebek, J. Angew.
Chem., Int. Ed. Engl. 1990, 29, 245–255. (c) Andrew, D.;
Kenneth, P. Chem. Rev. 1997, 97, 1251–1268.
3.3.12. 8-Phenyl-7,8-dihydro-6H-[2]benzoxecino[7,8-b]
pyrazine-5,10-dione (35). 19 mg (0.06 mmol) of 24 in
8 mL of dry CH2Cl2 were ozonized following the general
procedure described above. The crude was quenched with
10 mL of dry Me2S and chromatographed by preparative-
TLC using Hex/EtOAc (7:3) as eluent, to obtain 11 mg
10. Makgatho, M.; Anderson, R.; O’Sullivan, J.; Egan, T.; Freese,
J.; Cornelius, N.; Van Rensburg, C. Drug Dev. Res. 2000, 50,
195–202. (b) Andrade-Nieto, V.; Goulart, M.; da Silva, J. F.;
da Silva, M. J.; Pinto, M.; Pinto, A.; Zalis, M.; Carvalho, L.;
Krettli, A. Bioorg. Med. Chem. Lett. 2004, 14, 1145–1149.
11. Neves-Pinto, C.; Malta, V.; Pinto, M.; Santos, R.; Castro, S.;
Pinto, A. J. Med. Chem. 2002, 45, 740–743.
1
(53%) of 35. H NMR (CDCl3) d: 8.82 (1H, d, JZ2.5 Hz,
H-2), 8.54 (1H, d, JZ2.5 Hz, H-3), 8.20 (1H, d, JZ7.8 Hz,
H-11), 7.74 (2H, m, H-12CH-13), 7.56 (1H, m, H-14), 7.25
(3H, m, H-30CH-40CH-50), 7.03 (2H, m, H-20CH-60), 6.15
(1H, dd, JZ11.3, 2.8 Hz, H-8), 3.67 (1H, ddd, JZ15.0, 5.0,
3.6 Hz, H-6a), 2.72 (1H, ddd, JZ15.0, 12.4, 3.5 Hz, H-6b),
2.50 (1H, ddd, JZ12.3, 6.1, 3.5 Hz, H-7a), 2.22 (1H, m, H-
7b). 13C NMR (CDCl3) d: 202.2 (s, C-5), 165.3 (s, C-10),
153.1 (s, C-14b), 151.1 (s, C-4a), 144.8 (d, C-2), 140.4 (d,
C-3), 138.7 (s, C-15), 137.8 (s, C-14a), 133.6 (d, C-13),
133.4 (d, C-12), 132.2 (d, C-11), 129.4 (d, C-14), 128.5!2
(d, C-300CC-500), 128.3 (d, C-18), 126.3 (s, C-10a), 125.8!2
(s, C-2 CC-6 ), 77.2 (d, C-8), 39.2 (t, C-6), 32.9 (t, C-7).
MS m/z (rel. int): 344 (MC, 93), 316 (MCKCO, 43), 238
(MCKCO–Ph, 18), 183 (MCKOCH(Ph)(CH2)2CO, 95),
104 (PhCO, 100). HRMS: 344.1158 (calcd for C21H16N2O3
(MC) 344.1161).
12. Cartwright, D.; Chilton, W.; Benson, D. Appl. Microbiol.
Biotechnol. 1995, 43, 211–216. (b) Ligon, J.; Dwight, S.;
´
Hammer, P.; Torkewitz, N.; Hofmann, D.; Kempf, H.; Pee, K.
Pest. Manag. Sci. 2000, 56, 688–695.
13. Muller, M.; Sorrell, T. Prostaglandins Other Lipid Mediat.
1995, 50, 301–311.
14. Rewcastle, G.; Denny, W.; Baguley, B. J. Med. Chem. 1987,
30, 843–851. (b) Funayama, S.; Eda, S.; Komiyama, K.;
Omura, S. Tetrahedron Lett. 1989, 30, 3151–3154. (c) Wang,
S.; Miller, W.; Milton, J.; Vicker, N.; Stewart, A.; Charlton, P.;
Mistry, P.; Hardick, D.; Denny, W. Bioorg. Med. Chem. Lett.
2002, 12, 415–418. (d) Vicker, N.; Burgess, L.; Chuckowree,
I.; Dodd, R.; Folkes, A.; Hardick, D.; Hancox, T.; Miller, W.;
Milton, J.; Sohal, S.; Wang, S.; Wren, S.; Charlton, P.;
Dangerfield, W.; Liddle, C.; Mistry, P.; Stewart, A.; Denny,
W. J. Med. Chem. 2002, 45, 721–739. (e) Gamage, S.; Spicer,
J.; Rewcastle, G.; Milton, J.; Sohal, S.; Dangerfield, W.;
Mistry, P.; Vicker, N.; Charlton, P.; Denny, W. J. Med. Chem.
2002, 45, 740–743.
Acknowledgements
This work has been funded by Spanish MCYT (SAF2003-
04200-C02-02) and by ICIC (Instituto Canario de Investi-
´
gaciones del Cancer). E.P.S. thanks the ICIC for a
postdoctoral fellowship. The authors thank Dr. J. Platas
for valuable discussions regarding the structures of lower-
energy conformers.
´
´
15. (a) Ravelo, A.; Estevez-Braun, A.; Perez-Sacau, E. In Atta-Ur-
Rahman, Ed.; Studies in Natural Products Chemistry; Elsevier
Science: Amsterdam, 2003; Vol. 29 (part J), pp 719–760; and
´
references cited therein. (b) Ravelo, A.; Estevez-Braun, A.;
´ ´
Chavez, H.; Perez-Sacau, E.; Mesa-Siverio, D. Curr. Top.
Med. Chem. 2004, 4, 241–265.
´
´
16. Perez-Sacau, E.; Estevez-Braun, A.; Ravelo, A.; Ferro, E.;
Tokuda, H.; Mukainaka, T.; Nishino, H. Bioorg. Med. Chem.
2003, 11, 483–488.
References and notes
1. Stratmann, K.; Burgoyne, D.; Moore, R.; Patterson, G. J. Org.
Chem. 1994, 59, 7219–7226. (b) Tanaka, J.; Higa, T.
Tetrahedron Lett. 1996, 37, 5535–5538. (c) Mulzer, J.;
17. Nair, V.; Treesa, P. Tetrahedron Lett. 2001, 42, 4549–4551.
18. Kobayashi, K.; Mori, M.; Uneda, T.; Morikawa, O.; Konishi,
K. Chem. Lett. 1996, 451–452. (b) Sun, J.; Geiser, A.;
Frydman, B. Tetrahedron Lett. 1998, 39, 8221–8224.
19. Woo, G.; Snyder, J.; Wan, Z. Prog. Heterocyclic Chem. 2002,
14, 279–309.
¨
Ohler, E. Chem. Rev. 2003, 103, 3753–3786. (d) Labro, M.
In Macrolide Antibiotics; Schoenfeld, W., Kirst, H., Eds.;
Birkhaeuser: Basel, Switzerland, 2002; pp 37–52. (e)
Kobayashi, J.; Tsuda, M. Nat. Prod. Rep. 2004, 21, 77–93.
2. D’Ambrosio, M.; Guerriero, A.; Debitus, C.; Pietra, F. Helv.
Chim. Acta 1996, 79, 51–60.
20. Burton, S.; Kaye, P.; Wellington, K. Synth. Commun. 2000, 30,
511–522. (b) Huh, T. Bull. Korean Chem. Soc. 2000, 21,
369–370. (c) Huang, W.; Chen, C.; Lee, S. Heterocycles 2003,
60, 1573–1588.
3. Nicolaou, K.; Sasmal, P.; Rassias, G.; Reddy, M.; Altmann,
K.; Wartmann, M.; O’Brate, A.; Giannakakou, P. Angew.
Chem., Int. Ed. 2003, 42, 3515–3520.
´
21. Nazare, M.; Waldmann, H. Angew. Chem., Int. Ed. 2000, 39,
1125–1128. (b) Ohara, T.; Kume, M.; Narukawa, Y.;
Motokawa, K.; Uotani, K.; Nakai, H. J. Org. Chem. 2002,
67, 9146–9152. (c) Nicolaou, K.; Kim, D.; Baati, R. Angew.
Chem., Int. Ed. 2002, 41, 3701–3704. (d) Pilli, R.; Victor, M.
Tetrahedron Lett. 2002, 43, 2815–2818. (e) Williams, D.;
Patnaik, S.; Plummer, S. Org. Lett. 2003, 5, 5035–5038. (f)
Colby, E.; O’Brien, K.; Jamison, T. J. Am. Chem. Soc. 2004,
4. Kudoh, S.; Azuma, A.; Tamaoki, J.; Nakata, K.; Takizawa, H.;
Goto, H. In Macrolide Antibiotics, 2nd ed.; Omura, S., Ed.;
Academic: San Diego, CA, 2002; pp 533–569.
5. Yet, L. Chem. Rev. 2003, 103, 4283–4306.
6. Handa, M.; Ui, H.; Yamamoto, D.; Monma, S.; Iwai, Y.;
Sunazuka, T.; Omura, S. Heterocycles 2003, 59, 497–500.
¨
7. Kunze, B.; Jansen, R.; Sasse, F.; Hofle, G.; Reichenbach, H.
J. Antibiot. 1998, 51, 1075–1080. (b) Jansen, R.; Kunze, B.;
¨
126, 998–999. (g) Bulusu, M.; Waldstatten, P.; Tricotett, T.;
Schulz, G. Tetrahedron Lett. 2004, 45, 2527–2530. (h)
Schmidt, D.; Kwon, O.; Schreiber, S. J. Comb. Chem. 2004,
6, 286–292.
¨
Reichenbach, H.; Hofle, G. Eur. J. Org. Chem. 2000, 913–919.
8. Chu, M.; Mierzwa, R.; Xu, L.; He, L.; Terracciano, J.; Patel,
M.; Gullo, V.; Black, T.; Zhao, W.; Chan, T.; McPhail, A.
J. Nat. Prod. 2003, 66, 1527–1530.
22. Garcia-Rubio, S.; Meinwald, J. J. Org. Chem. 2001, 66,

´
E. Perez-Sacau et al. / Tetrahedron 61 (2005) 437–445
445
1082–1096. (b) Lazarova, T.; Binet, S.; Vo, N.; Chen, J. Org.
Lett. 2003, 5, 443–445.
6, 1175–1178. (c) Torii, S.; Inokuchi, T.; Kondo, K. J. Org.
Chem. 1985, 50, 4980–4982. (d) Grant, P.; Hanton, L.; Tsai, S.
Aust. J. Chem. 1985, 38, 1461–1470. (e) Moricz, A.; Gassman,
E.; Bienz, S.; Hesse, M. Helv. Chim. Acta 1995, 78, 663–669.
25. Hunt, K.; Gireco, P. Org. Lett. 2000, 2, 1717–1719.
26. PC-Model version 7.0 was used to carry out the GMMX
calculations.
23. Borowitz, I.; Gonis, G.; Kelsey, R.; Rapp, R.; Williams, G.
J. Org. Chem. 1966, 31, 3032–3037.
24. Goulart, M.; Cioletti, A.; de Souza, J.; de Simone, C.;
Castellano, E.; Emery, F.; de Moura, K.; Pinto, M.; Pinto, A.
Tetrahedron Lett. 2003, 44, 3581–3585. (b) Baskaran, S.;
Islam, I.; Raghavan, M.; Chandrasekaran, S. Chem. Lett. 1987,
27. Wiberg, K. J. Org. Chem. 2003, 68, 9322–9329.