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Enantiomerically Pure УWingedФ Spirane Porphyrazinoctaols.

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Enantiomerically Pure "Winged" Spirane
Porphyrazinoctaols""
Andrew S. Cook, D. Bradley G. Williams,
Andrew J. P. White, David J. Williams, Steven J. Lange,
Anthony G. M. Barrett,* and Brian M. Hoffman*
Dedicated to Professor Dieter Seebach
on the occasion of his 60th birthday
Herein we report the first synthesis of porphyrazinoctaol
derivatives-the enantiomerically pure, "winged" spirane porphyrazines-through the use of a simple, reliable strategy based
on the Ley dispoke protection procedure.['] We earlier described
the synthesis of porphyrazinoctathiol derivatives by macrocyclization of 2,3-bis(benzylthio)maleonitrile with magnesium
propoxide in propanol,121their transmetalation, and reductive
deben~ylation.[~]
The octathiol thus obtained exhibited diverse
coordination chemistry. Complexes were isolated with four
metal cations peripherally bonded to the eight thiolate residues
by either bidentate (S-S) or tridentate (S-meso-N-S) coordination, in addition to internal metal- ion complexation. These star
porphyrazines readily lend themselves to the study of indirect
metal-metal interactions through the porphyrazine 7~ system
and are unique in that the binding mode may be selected at will.
We subsequently reported the synthesis and characterization of
various porphyrazinoctamine derivatives as well as the formation of charge-transfer complexes with tetracyanoquinodimethane (TCNQ) and C,, .I4]This paper presents the synthesis of chiral porphyrazines 5 and 6.15)
Reaction of excess L-( +)-dimethyl tartrate (1) with 3,3',4,4tetrahydro-6,6'-bi-2H-pyran (bis-DHP)['. 61 in diethyi ether in
the presence of hydrogen chloride gave the dispiroketal 2 in a
60 YOyield (Scheme 1). Strong anomeric effects dominate the
""I(""
a)
MeOOC
COOMe
1
~
2
4
o
w
0
MeOOC
Ad,
0
0
4
5M=Mg
6M=2H
Scheme 2
d)
3
b)
(PrO),Mg, PrOH, 100 C. 14 h, 45%, b) AcOH. 20 C, 16 h, 78%
Confirmation of structure was obtained from a single crystal
X-ray determination of 6 (Figure I).[*] The molecule has noncrystallographic D,symmetry; the central core is planar to with-
b)
MeooTOO
stereochemical outcome of the reaction under thermodynamic
conditions, which gives rise to only one diastereoisomer of
2.". The chirality inherent in the tartrate induces sterogenicity
at the ketal centers and results in a product in which the
methoxycarbonyl moieties are equatorial. Monoiodination, followed by base-mediated anti-dehydroiodination, afforded chiral alkene 3 (53 %). Amide formation and dehydration proceeded smoothly to give dinitrile 4 in 77 O/O overall yield. A solution
of 4 and magnesium propoxide in propanol under reflux provided the magnesium porphyrazine 5 in 45% yield. Strong acids
such as trifluoroacetic acid rapidly demetalated 5 ; unfortunately these conditions also caused degradation of the macrocycle.
However, reaction with glacial acetic acid resulted in clean
demetalation without epimerization and production of the D,symmetric, enantiomerically pure porphyrazine 6 (Scheme 2).
COOMe
3
O H 0
NC
4
CN
-
Scheme 1 a) Bis-DHP, HCI, Et,O, O'C, 16 h; b) lithium 2,2,6.6-tetramethylpiperidide. TH E - 78 'C. then I, in THF. - 78 'C
0°C. c) NH,, MeOH. 20 'C.
4 d ; d j (CF,CO),O, pyridine, -30'C + 20"C, 3 h.
I*] Prof Dr. A. G. M. Barrett. A. S. Cook, Dr D. B. G. Williams.
Dr. A. J. P. White, Prof. Dr. D. J. Williams
Department of Chemistry
Imperial College of Science, Technology, and Medicine
South Kensington, London SW72AY (UK)
Fax Int. code +(171)594-5805
e-mail: m.stow(u ic.ac.uk
Prof. Dr. B. M. Hoffman, S. J. Lange
Department of Chemistry, Northwestern University
Evanston, 1L 60208 (USA)
Fax. Int. code +(847)491-7713
e-mail. bmh(u mercury.chem.nwu.edu
[**I
Figure 1. Crystal structure of 6
A.
We thank Glaxo Group Research Ltd. for the generous endowment
(A.G.M.B.), the Wolfson Foundation for establishing the Wolfson Centre for
Organic Chemistry in Medical Sclenceat Imperial College, the Engineering and
Physical Sciences Research Council, the National Science Foundation, NATO,
the Foundation for Research and Development (South Africa). and Zeneca for
generous support of our studies.
760
0 VCH Veriug.FReseNsrhuftmhH, 0-69451
Weinhein?,1997
in 0.08
The presence of hydrogen atoms on the nitrogen
centers distorts the potential D, symmetry of the non-hydrogen
atoms: the transannular porphyrin N . . N distances differ by
about 0.15 A.Spectroscopic data for 6 reflect this distortion:[91
its electronic absorption spectrum exhibits a split Q band with
peaks at 632 and 554 nm in addition to a less intense peak at
427 nm and the Soret band["] at 338 nm.
OS70-0833iY7:3607-0760 $ 17.50+ .SO/O
Angew. Chem. I I I I . Ed. Engl. 1997. 36, N o . 7
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The electrochemical properties of 5 and 6 were studied by
cyclic voltammetry in dichloromethane.llll The freebase porphyrazine 6 exhibits one reversible oxidation at Eli, = 0.73 V
(vs. Fc+/Fc, Fc = ferrocene; Figure 2). Comparison ofthe elec-
+
I
I
I
0
-1
-2
Figure 2 Cyclic holtammograms of 6 and other porphyrazines (potential vs
Fc+ :I+).
1
trochemical properties of 6 with those of H2[pz(S-Et),lr1*]and
H , [ ~ z ( P ~ ) , ] [reveals
' ~ ~ that all have similar first oxidation
potentials ( + 0.65-0.73 V vs. Fc+/Fc). In contrast, the
H,[~Z(N-M~,),][~I
macrocycle is more easily oxidized by 1.00 V.
This is consistent with the primary function of 0-alkyl and
S-alkyl substituents being o donors, but of N-alkyl substituents
being strong x donors. Compound 6 exhibits reversible ring
reductions at E,,, = - 1.22 and - 1.66 V (vs. Fc+/Fc). Incorporation of a Mg" ion in the porphyrazine core (5) broadens the
first reduction wave and shifts it by 300 mV to a more negative
potential; any second ring reduction is shifted out of the
solvent potential window. The ease of reduction of the differently functionalized porphyrazines follows the order: H,[pz(SEt),], -0.95 V>H,[pz(O-alkyl),],
- 1.22 V>H,[pz(Pr),],
-1.37 V>H,[pz(N-Me,),], -1.61 V. These data are summarized in Table 1.
Table 1. Electrochemical data for 6 and other porphyrazines in dichloromethane
(potential vs Fc+:Fc)
5
6
H,[pz(S-Et),l
H,[pz(N-Me,),l
H,[pz(W,I
+101[a]
+1.09[a]
+ 1 361al
-0 06 (76)
-
+0.46(115)
+0.73(90)
+0.65 (80)
-0.27 (72)
+0.68 (100)
-1.53(210)
-1.22(100)
-0.95 (SO)
- 1.61 (80)
-1.37(70)
~
-1.66(125)
-1.27 (90)
-
[a] A coupled chemical reaction follows the electrochemical step.
We have established a rapid, reliable approach for preparing
porphyrazinoctaol derivatives. The simple, high-yielding synthesis represents a convenient entry to enantiomerically pure
porphyrazine systems. We are presently investigating the use of
such porphyrazines in organic and coordination chemistry.
Studies on deprotection and metal-ion complexation of 6 (and
related compounds) will be reported in due course.
Received: October 21. 1996 [Z9676IE]
German version: Angew Chem 1996, 109,806-807
Angew. C h ~ n lIn/.
. Ed. Engl. 1997. 36. No 7
C
Keywords: chirality . cyclic voltammetry
protecting groups spiro compounds
*
porphyrinoids
*
[I] S. V. Ley. M Woods. A. Zanotti-Gerosa, S ~ w i h e . ~1992.
~ . ~ 52. S. V. Ley, R
Leslie, P. D. Tiffin. M. Woods. Tetrahedron Luri. 1992.33.4767: R Downham.
K. S. Kim. S. V. Ley. M. Woods, ihid. 1994. 35. 769; D A. Entwistle. A B.
Hughes. S. V. Ley. G. Visentin, ihrd. 1994. 35. 777
[2] C. J. Schramm, B M. Hoffman, Inorg. CIwn. 1980. 1Y. 383
131 C. S. Velazquez. W E. Broderick. M. Sabat, A. G. M. Barretl. B. M. Hoffman.
J Am Cliem Sot. 1990, 112. 7408, C. S. Velazquez. G . A. Fox, W E. Broderick. K. A. Andersen. 0 . P. Anderson. A G. M. Barrett. B. M. Hoffman. ihid
1992, lf4.7416; C. S. Velazquez. T F Baumann. M M Olnistead. H . Hope,
A. G. M. Barrett, B. M. Hoffman, ihid. 1993, 115. 9997.
[4] N. S. Mani, L. S. Beall. T. Miller, 0 . P. Anderson. H. Hope. S R. Parkin, D. J.
Williams, A. G. M. Barrett, B. M Hoffman, J Chew Soc. Clieni. Comnrun.
1994. 2095; D. M. Eichhorn. S. Yang, W. Jarrell, T. F. Baumann, 1.S. Beall.
A. J. P. White, D. J. Williams. A. G. M. Barrett. B. M. Hoffman. /hid 1995.
1703.
[5] Kopranenkov et al. have reported a synthesis of 2,3-di(alko~y)-and 2.7.12.17tetra(a1koxy)porphyrazines. However, in our hands, this procedure failed to
provide characterizable pigments V. N. Kopranenkov. L S. Goncharova.
E. A. Luk'yanets, J Org. Cheni. USSR 1979, IS, 962; V. N. Kopranenkov. L. S.
Goncharova, L. E. Marinina. E. A Luk'yanets, Clieniisrri. of Heterocjclic
Compounds U S S R 1982,18,1269 The synthesis of some cron n ether annulated
porphyrins has been reported: H Uno, T. Ogawa. N Ono. liwuliedron Lert.
1996, 37. 3133.
161 S. Ghosal, G. P. Luke. K. S. Kyler. J. Org. Chem. 1987. 52. 4296.
[7] P. Deslongchamps, S/ereoe/erfronrcEflecrs in Orgmic SJnihesic. Pergamon,
Oxford. 1983.
[8] Crystal data for 6 - C,,H,,N,O,,.
M, =1107.2, orthorhombic. space group
V = 5768(2) A3. Z = 4,
P2,2,2, u = 16.895(5), h = 23.715(4). c = 14.396(2)
pralcd=1.28gcm-3. p(Cux,) = 7 . 9 c m - ' . F(OO0) = 2344, T = 173 K. A flaky,
iridescent, green plate of dimensions 0.27 x 0 27 x 0 03 mm nas used. The 3973
independent reflections were measured on a Siemens P4. RA diffractometer
with Cu,, radiation (graphite monochromator) and w scans. The structure was
solved by direct methods. Despite collecting the data with copper radiation and
a rotating anode operating at 14 kW over a period of several days at reduced
temperature, the diffracted intensities were still very weak. and the number of
observed data severely limited. Consequently. the 24 non-hydrogen atoms of
the porphyrazine core, which are not normally subject to significant anisotropic vibration. were refined isotropically, and only the non-hydrogen atoms ofthe
peripheral substituents were treated anisotropically Refinement by full-matrix
least squares based on F 2 gave R , = 0 078 and W R , = 0.191 for 2710 independent observed reflections []&I >4u(IF,I). 205110 ] and 602 parameters. The
absolute chirality of the structure could not be determined crystallographically
and was assigned on the basis of the known absolute stereochemistry of 1 and
the expected stereochemical bias of dispoke protections [ I , 71 Crystallographic
data (excluding structure factors) for the strncture reported in this paper have
been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-100184. Copies of the data can be obtained
free of charge on application to The Director, CCDC. 12 Union Road,
Cambridge CB21EZ. UK. (fax: Int. code +(1223)136-033; e-mail:
deposit@chemcrys.cam.ac.uk).
[9] Selected data for 6. m.p. = 300°C (Et0Ac;hexane. decomp.); IR (CHCI,):
= 3313,2953, 1662, 1619, 1216, 1185, 1103. 971. 894. 755 c m - l : UV,'Vis
(CHCI,): i,,, (log E ) = 338 (4.20), 427 (3.68). 554 (3.75). 632 (3.83) nm;
' H N M R (300 MHz, CDCI,). 6 = 4.27 (td, J = 10.8 and 4.7 Hz. XH). 3.72 (d,
J = 9.5 Hz, XH), 2.76 (dd, J = 12.0 and 4.1 Hz, 8 H). 2.62 (d. J = 13.3 Hz, 8 H).
2.21 (dd,J=13.2and4.5Hz,8H),2.09(d,J=12.8Hz,XH).1.90-1.77(m,
16H). -3.51 (br.s.2H); "CNMR(75 MHz,CDCI,):6 = 143.3.137.6, 100.1.
62.5, 28.9, 24.9, 18 3: HRMS: calcd m:; for C,,H,,N,O,,.
1107.4675 ( M
+ H + ) ; found: 1107.4706.
[lo] M. Goutermann in The Porph!rrns, Vol. 2 (Ed.: D. Dolphin). Academic Press,
New York. 1978, chap. I
[l I ] Cyclic voltammetric measurements were carried out with a Cypress Systems CS-1087 computer-controlled potentiostat. A single compartment cell
was used with a platinum disk working electrode, AgiAgCl reference electrode,
and silver wire auxiliary electrode. Measurements were made in dichloromethane. freshly distilled from calcium hydride, with recrystallized tetra-nbutylammonium hexafluorophosphate as supporting electrolyte. Solutions
containing approximately lo-' M analyte (0.1 M Bu,NPF,) were deaerated for
several minutes by purging with nitrogen. Ferrocene was added as an internal
reference for all measurements, and all E , values were calculated from
(Ens Ep,)/2at a scan rate of 110 mVs-'
[12] For electroreduction of octakis(methy1thio)porphyrazines in pyridine. see
L. A. Bottomley, W. J. H. Chiou, J. Eleclrounul. Climi. 1986. 198,331
[13] This macrocycle was synthesized by a slight modification o f t h e procedure of
Fitzgerald and co-workers: J. Fitzgerald. W Taylor, H. Owen. Synthesis 1991.
686.
A,
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