8474
D. Rega´s et al. / Tetrahedron Letters 44 (2003) 8471–8474
there is some asynchronicity, with the carbonꢀcarbon
bond formed to a larger extent in the transition state
(42–44%) than the carbonꢀoxygen bond (25–27%). The
introduction of the methyl groups on the allene
enhances this asynchronicity.
mmol) in diethyl ether (2 mL). The reaction was stirred
overnight and then Et3N (1 mL) was added followed by
water. The reaction was extracted with diethyl ether
(3×15 mL), dried and concentrated. After flash column
chromatography (3% EtOAc in hexanes), 8 was obtained
1
as a clear oil (18 mg, 18%). H NMR (400 MHz, C6D6)
In conclusion, we have found that the intramolecular
hetero Diels–Alder reaction of vinyl allenes with alde-
hydes can occur to give polycyclic compounds, pro-
vided that the right substitution pattern and length of
tether are used. The reaction proceeds thermally, with-
out Lewis acid, in several of the examples studied.
l 6.11 (s, 1H), 5.44 (s, 1H), 4.71 (t, J=7.0 Hz, 1H), 4.23
(dd, J=4.5, 11.9 Hz, 1H), 2.27–2.32 (m, 3H), 2.14–2.16
(m, 1H), 1.99–1.79 (m, 4H), 1.58–1.64 (m, 2H), 1.08–1.22
(m, 2H); 13C NMR (100 MHz, C6D6) l 144.5, 139.5,
121.0, 113.9, 77.0, 76.1, 34.5, 33.6, 31.2, 30.0, 28.3, 25.1;
HRMS (EI) m/z calcd for C12H16O 176.1201, found
176.1205.
13. All new compounds reported exhibit spectroscopic data
(1H and 13C NMR, COSY, HSQC and HMBC) consis-
tent with the proposed structures.
Acknowledgements
14. Stonehouse, J.; Adell, P.; Keeler, J.; Shaka, A. J. J. Am.
This research was made possible by grant BQU2001-
3184 from the Spanish Ministry of Science and Tech-
nology. D.R. thanks the M.E.C. for a FPU fellowship.
Chem. Soc. 1994, 116, 6037.
15. Marshall, J. A.; Shearer, B. G.; Crooks, S. L. J. Org.
Chem. 1987, 52, 1236.
16. Other vinyl allenals 17 and 18 with a one carbon atom
shorter and longer tether, respectively, than those studied
in this work were also prepared following the same
strategy and subjected to the same reaction conditions.
As expected from the literature data neither one reacted
to give cyclization products.5
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