4684
S. Sabui et al. / Tetrahedron Letters 50 (2009) 4683–4684
HO
R
R
a
c
10
R
O
O
OH
O
O
R = H 1
R = Br 3
R = Cl 4
R = OH 16
R = OTs 17
2
d
e
1 R = H
3 R = Br
4 R = Cl
b
Scheme 3. Reagents and conditions: (a) LiAlH4, THF, reflux, 5 h, 88%; (b) p-TsCl, Py,
DMAP, 22 h, 91%; (c) NaBH3CN, HMPA, 130 °C, 20 h, 65%; (d) NBS, acetonitrile, rt,
overnight, 98%; (e) NCS, acetonitrile, rt, overnight, 80%.
a
O
OH
N
CO2Et
sodium cyanoborohydride in HMPA furnished helianane 1 in 65%
yield, which was spectroscopically identical with a previous
sample.4b Overnight treatment of helianane with N-bromosuccini-
mide effected quantitative conversion to bromohelianane 3, whose
spectral data were comparable with those reported (Scheme 3).3,8
Similarly, overnight treatment of 1 with N-chlorosuccinimide fur-
nished chlorohelianane 4 in 80% yield whose spectral data also
were comparable with the reported values.3,8
In summary, we have described an expeditious synthesis of
helianane and the C-10 halogenated heliananes employing simple
reagents and readily accessible reaction conditions to furnish the
target molecules in good overall yield.
6
5
b
Mes
Mes
Cl
N
Ru
Pcy3
O
Cl
Ph
7
CO2Et
A
c
d
Acknowledgements
O
O
WesincerelyacknowledgethefinancialsupportfromtheDepart-
ment of Science and Technology, Government of India. S.G. thanks
the Council of Scientific and Industrial Research, New Delhi for a
research fellowship. We thank Professor Fernando Reyes for provid-
ing us copies of the spectra of C-10 bromo- and chloroheliananes.
CO2Et
CO2Et
8
10
O
CO2Et
O
EtO2C
References and notes
9
1. Harrison, B.; Crews, P. J. Org. Chem. 1997, 62, 2646–2648.
2. Macias, F. A.; Varela, R. M.; Torres, A.; Molinillo, J. M. G. Tetrahedron Lett. 1993,
34, 1999–2002.
3. Martín, M. J.; Berrué, F.; Amade, P.; Fernández, R.; Francesch, A.; Reyes, F.;
Cuevas, C. J. Nat. Prod. 2005, 68, 1554–1555.
Scheme 1. Reagents and conditions: (a) K2CO3, ethyl a-bromopropionate, acetone,
reflux, 7 h, 90%; (b) LDA, 1-bromo-3-butene, HMPA, THF, À78 °C to rt, 7 h, 80%; (c)
Grubbs 2nd generation cat. (15 mmol %), dichloro methane, 9 h, 50%; (d) H2/Pd-C
(10%), ethanol, 4 h, 98%.
4. (a) Stefinovic, M.; Snieckus, V. J. Org. Chem. 1998, 63, 2808–2809; (b) Sabui, S. K.;
Venkateswaran, R. V. Tetrahedron Lett. 2004, 45, 9653–9655; (c) Ghosh, S.;
Tuhina, K.; Bhowmik, D. R.; Venkateswaran, R. V. Tetrahedron 2007, 63, 644–
651; (d) Sen, P. K.; Biswas, B.; Venkateswaran, R. V. Tetrahedron Lett. 2005, 46,
8741–8743.
5. Divakar, K. J.; Rao, A. S. Synth. Commun. 1976, 423.
a
6. All new compounds reported here gave spectral data consistent with the assigned
structures. Selected spectral data: For 8: IR 1749 cmÀ1 1H NMR (300 MHz, CDCl3)
;
O
OH
d 1.23 (t, J = 7.1, 3H), 1.52 (s, 3H), 2.02 (s, 3H), 2.14 (dd, J = 7.3, 14.4 Hz, 2H), 2.25
(s, 3H), 2.35 (dd, J = 6.5, 14.2 Hz, 2H), 4.15 (q, J = 7.1 Hz, 2H), 5.83 (t, J = 6.5 Hz,
1H), 6.78 (d, J = 7.8 Hz, 1H), 6.96 (s, 1H), 7.07 (d, J = 7.8 Hz, 1H); 13C (75 MHz,
CDCl3) d 14.5, 21.3, 21.9, 24.4, 30.0 35.1, 61.4, 94.5, 122.2, 124.9, 125.0, 127.1,
11
12
b
132.2, 137.9, 138.4, 154.3, 174.1. For 10: IR 1751 cmÀ1 1H NMR (300 MHz,
;
CDCl3) d 1.30 (m, 3H), 1.47 (s, 3H), 1.55, 1.60 (2s, 3H) 1.72–1.82 (m, 2H), 1.84–
2.07 (m, 4H), 2.29 (s, 3H), 3.10–3.19 (m, 1H), 4.21 (m, 2H), 6.83, 6.93 (2s, 1H),
6.88 (d, J = 7.5 Hz, 1H), 6.99 (d, J = 7.6 Hz, 1H). 13C (75 MHz, CDCl3) d 14.5, 19.6,
19.7, 21.1, 22.8, 25.7, 28.8, 30.0, 33.1, 34.7, 40.8, 61.4, 81.2, 81.6, 124.4, 125.2,
126.2, 126.3, 135.3, 135.5, 136.9, 137.0, 153.3, 153.8, 173.8, 174.4. For 15 (one
c
O
13
O
diastereomer): IR 1752 cmÀ1 1H NMR (300 MHz, CDCl3) d 1.24 (m, 6H), 1.31 (m,
;
CO2Et
CO2Et
3H), 2.19 (s, 3H), 2.23 (m, 1H), 2.69 (m, 1H), 3.75–3.76 (m, 1H), 4.20–4.26 (q,
J = 7.2 Hz, 2H), 5.35 (m, 1H), 5.59 (dd, J = 6.3, 10.8 Hz, 1H), 6.74 (s, 1H), 6.82 (d,
J = 8.4 Hz, 1H), 6.97 (d, J = 7.8 Hz, 1H); 13C (75 MHz, CDCl3) d 14.3, 19.8, 20.9,
22.3, 33.1, 36.1, 61.3, 82.8, 120.7, 120.8, 125.2, 125.7, 126.8, 136.9, 140.3, 153.0,
173.8. For 3: 1H NMR (300 MHz, CDCl3) d 1.23 (s, 3H), 1.26 (d, J = 6.9 Hz, 3H), 1.
40 (m, 1H), 1.41 (s, 3H), 1.55 (m, 4H), 1.75 (m, 1H), 2.31 (s, 3H), 3.15 (m, 1H),
6.77 (s, 1H), 7.31 (s, 1H); 13C (75 MHz, CDCl3) 21.0, d 21.7, 22.5, 26.5, 29.1, 29.7,
38.0, 39.4, 81.4, 119.7, 127.3, 129.9, 134.9, 141.6, 152.3. For 4: 1H NMR
(300 MHz, CDCl3) d 1.23 (s, 3H), 1.26 (d, J = 6.9, 3H), 1.39 (m, 1H), 1.41 (s, 3H),
1.58 (m, 4H), 1.72 (m, 1H), 2.29 (s, 3H), 3.16 (m, 1H), 6.76 (s, 1H), 7.13 (s, 1H);
13C (75 MHz, CDCl3) d 19.8, 21.2, 21.9, 26.6, 29.2, 29.8, 37.6, 39.5, 81.5, 116.2,
126.8, 127.4, 133.1, 141.3, 151.7.
14
d
e
O
O
CO2Et
CO2Et
10
15
7. Sarkar, D.; Venkateswaran, R. V. Synlett 2008, 5, 653–654.
8. We attribute the minor deviations in the spectral values to a change of solvent in
our case (CDCl3) and possibility of conformational isomers (see Ref. 2).
Scheme 2. Reagents and conditions: (a) SnCl4, dichloro methane, 0 °C to rt, 80%; (b)
K2CO3, ethyl -bromopropionate, acetone, reflux, 6 h, 81%; (c) LDA, allyl bromide,
a
HMPA, THF, À78 °C to rt, 8 h, 80%; (d) Grubbs 2nd generation cat. (1.5 mmol %),
dichloro methane, 24 h, 90%; (e) H2/Pd-C (10%), ethanol, 3 h, 98%;