the benzazaphosphol moiety is more sterically demanding than
the phenyl ring linked to the phosphorus and the larger steric
interaction with the phenyl ring on C4 accelerates the opening
of the oxaphosphetane 5e-trans compared to its isomer 5e-cis.
These results support the participation of oxaphosphetanes in
the olefin synthesis through phosphazenes.
In summary, a new type of bicyclic oxaphosphetane system
has been obtained and characterized in a tandem process
involving the first ortho and a dimetallation of P-alkyl-P,P-
(
diphenyl)(N-methoxycarbonyl)phosphazenes and subsequent
addition of aldehydes and ketones. When heated in toluene, they
afford olefins quantitatively and stereospecifically.
This research was partially supported by the European
Community (FEDER Project 1FD97-1651), CICYT
(BQU2000-0219) and FICYT (PR-01-GE-4).
Notes and references
‡
C
Crystal data for 5a: Data for the X-ray structure analysis of 5a-trans:
24NO P (Mr 341.37); monoclinic, space group C2/c, a
Fig. 1 Crystal structure of 5a-trans (ORTEP). Selected bond lengths (Å)
and bond angles (°): P2–O1 1.725(2), P2–N5 1.812(2), P2–C3 1.862(2),
P2–C8 1.824(2), P2–C13 1.833(2), C3–C4 1.547(3), O1–C4 1.433(3), O1–
P2–N5 166.09(9), O1–P2–C3 77.25(9), P2–C3–C4 87.6(1), O1–C4–C3
20
H
2
=
=
13.6367(3), b = 15.4090(3), c = 18.5552(3) Å, b = 108.422(1)°, V =
3
23
21
3699.2(1) Å , Z = 8, Dx = 1.226 Mgm , m(Cu Ka) = 1.400 mm . Data
collection at 200(2) K. A total of 28833 reflections were collected, 3462
unique reflections, Rint = 0.069. 2486 reflections were observed with
97.4(2), C3–P2–C8 132.0(1), C3–P2–C13 115.0(1), C8–P2–C13
2
2
2
2
112.8(1).
I > 2s(I). Final value of R1 (F > 2s(F )) = 0.0484, wR2 (F > 2s(F )) =
3
2
0
.1199. Residual electron density 0.191/20.388eÅ . CCDC reference
number 181221. See http://www.rsc.org/suppdata/cc/b2/b212708c/ for
crystallographic files in CIF or other electronic format.
Table 1 Yields (%) and dr of the oxaphosphetanes 5 obtaineda
Comp.
R1
R2
R3
R4
Trans+cis
Yield
1
(a) H. Schmidbaur and G. Jonas, Chem. Ber., 1967, 100, 1120; (b) F.
López-Ortiz, E. Peláez-Arango, B. Tejerina, E. Pérez-Carreño and S.
García-Granda, J. Am. Chem. Soc., 1995, 117, 9972; (c) K. Izod, Coord.
Chem. Rev., 2002, 227, 153.
(a) C. G. Stuckwisch, J. Org. Chem., 1976, 41, 1173; (b) A. Steiner and
D. Stalke, Angew. Chem., Int. Ed. Engl., 1995, 34, 1752.
(a) A. W. Johnson, Ylides and Imines of Phosphorus, John Wiley, New
York, 1993, p. 403; (b) J. M. Álvarez-Gutiérrez and F. López-Ortiz,
Chem. Commun., 1996, 1583; (c) J. M. Álvarez-Gutiérrez, E. Peralta-
Pérez, I. Pérez-Álvarez and F. López-Ortiz, Tetrahedron, 2001, 57,
5
5
5
5
5
5
a
a
b
c
d
e
f
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
Bu
Me
H
H
H
(CH
Me
Me
Pri
Bu
4-MeO-C
49+51
23+73
40+60
95+5
93
87
93
82
62
89
t
6 4
H
2 2
2
3
2
CH CH CH CH )
2
2
n
b
Ph
Ph
76+24
10+90
The diastereoisomers were separated by precipitation in diethyl ether or
b
column chromatography. Trans/cis descriptors indicate the orientation of
the methyl groups, in both stereoisomers the phenyl rings are cis.
3
075; (d) C. M. Andújar, I. Pérez-Álvarez and F. López-Ortiz,
Tetrahedron, 2002, 58, 2569.
4
F. Baier, Z. Fei, H. Gornitzka, A. Murso, S. Neufeld, M. Pfeiffer, I.
Rüdenauer, A. Steiner, T. Stey and D. Stalke, J. Organomet. Chem,
2002, 661, 173and references therein.
oxaphosphetane was the required intermediate previous to the
11
carbon–carbon double bond formation step. Several isolable
12
5 (a) A. Müller, B. Neumüller and K. Dehnicke, Z. Anorg. Allg. Chem.,
1997, 623, 1306; (b) C. M. Ong and D. W. Stephan, J. Am. Chem. Soc.,
1
,2-oxaphosphetanes have been reported. Those having a
13
bicyclic structure showed increased stability.
1
999, 121, 2939; (c) A. Kasani, R. P. Kamalesh Babu, R. McDonald and
Heating oxaphosphetanes 5c–e to 90–115 °C in toluene-d
8
R. G. Cavell, Angew. Chem., Int. Ed., 1999, 38, 1483.
gave quantitatively olefins 6 and benzazaphosphol 7 (Scheme 2,
see electronic supplementary information†). It is worth noting
the stereospecific thermolysis of 5e-cis and 5e-trans afforded
the olefins 6c and 6d, respectively. 31P NMR monitoring of the
olefin formation showed a first order kinetic with respect to 5.14
The highest rate of decomposition was observed for 5d, a fact
that might be a consequence of the ring strain imposed by the
tricyclic system involving the oxaphosphetane moiety. 5e-trans
was less resistant than 5e-cis to thermolysis, which suggests that
6
P. B. Hitchcock, M. F. Lappert and Z-X. Wang, Chem. Commun., 1997,
1
113.
7 The descriptors trans/cis, indicate the spatial relationship between the
P-phenyl ligand and the highest rank substituent linked to the
stereogenic carbons C3 or C4 of the oxaphosphetane.
8
9
E. Vedejs and C. F. Marth, J. Am. Chem. Soc., 1989, 111, 1519.
The structure of all compounds was determined by performing the same
NMR analysis described for 5a-trans.
1
1
1
0 E. Peralta-Pérez and F. López-Ortiz, Chem. Commun., 2000, 2029.
1 E. Vedejs and M. J. Peterson, Adv. Carbanion Chem., 1996, 2, 1.
2 (a) T. Kawashima and R. Okazaki, Synlett, 1996, 600; (b) O. I.
Kolodiazhnyi and R. Schmutzler, Synlett, 2001, 1065; (c) M. Appel, S.
Blaurock and S. Berger, Eur. J. Org. Chem., 2002, 1143.
1
3 (a) H. A. E. Aly, J. H. Borlow, D. R. Russell, D. J. H. Smith, M.
Swindles and S. Trippett, J. Chem. Soc., Chem. Commun., 1976, 449;
(b) T. Kawashima, K. Kato and R. Okazaki, J. Am. Chem. Soc., 1998,
1
20, 6848; (c) I. V. Shevchenko, R. N. Mikolenko, E. Lork and G. V.
Röschenthaler, Eur. J. Inorg. Chem., 2001, 2377; (d) S. Kojima, M.
Sugino, S. Matsukawa, M. Nakamoto and K-Y. Akiba, J. Am. Chem.
Soc., 2002, 122, 7674.
1
4 Rate constants k, of the decomposition reactions: 5a, k(115 °C) = 1.27
25
21
24 21
3
10
s
; 5b, k(90 °C) = 7.8 3 10
s
; 5c, k(115 °C) = 1.8 3
(see electronic supporting
5
25 21
1
02 s21; 5d, k(115 °C) = 4.22 3 10
s
Scheme 2 Synthesis of olefins 6 through thermolysis of 5.
information†).
CHEM. COMMUN., 2003, 856–857
857