Porpholactams and chlorolactams: Replacement of a β,β′- double bond in meso-tetraphenyl-porphyrin and -chlorin by a lactam moiety

Article abstract of DOI:10.1039/c1cc12955d

Reaction of meso-tetraphenylporpholactone with hydrazine converts the lactone moiety to an N-aminolactam. It also reduces the opposite pyrrolic moiety of both the starting material and the N-aminolactam, generating chlorin-like chlorolactone and N-aminoch

Full text of DOI:10.1039/c1cc12955d

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Porpholactams and chlorolactams: replacement of a b,b -double bond in
meso-tetraphenyl-porphyrin and -chlorin by a lactam moietywzy
Joshua Akhigbe, John Haskoor, Matthias Zeller and Christian Bruckner*
¨
a
a
b
a
Received 19th May 2011, Accepted 7th June 2011
DOI: 10.1039/c1cc12955d
Reaction of meso-tetraphenylporpholactone with hydrazine
converts the lactone moiety to an N-aminolactam. It also
reduces the opposite pyrrolic moiety of both the starting material
and the N-aminolactam, generating chlorin-like chlorolactone
and N-aminochlorolactam, respectively. Reductive N–N cleavage of
the N-aminoporpholactam generates the parent porpholactam.
Several syntheses of meso-tetraarylporpholactone 4 from
the corresponding porphyrins have been described since their
5
,6
discovery by Crossley and King in 1984. Using a two-step
protocol described by us, porpholactone 4 can be routinely
6
made in gram quantities from meso-tetraphenylporphyrin 1,
allowing its further exploration.
Thus, reaction of porpholactone 4 with hydrazine hydrate
in refluxing THF forms, over the course of several days,
one minor and two major products of the compositions
C H N O (5), C H N O (6) and C H N O (7), respec-
Porphyrin analogues that maintain the principal porphyrinoid
macrocycle structure, but in which one (or two) C or N atoms
were exchanged for C, N, O, S, etc., are part of the canon of
4
3
30
4
2
43 30
6
43 32
6
1
methods toward the fundamental study of porphyrins.
tively (determined by ESI + HR-MS) (Scheme 1).
Examples of such analogues to meso-tetraphenylporphyrin
The composition of product 5 suggests that a two-hydrogen
reduction of the starting porpholactone 4 (C H N O ) had
2
3
1) are heteroporphyrins, N-confused porphyrin 2, imidazo-
(
4
3
28
4
2
4
loporphyrin 3, porpholactone 4, or its carbaporpholactone
5,6
taken place. Indeed, the UV-vis spectrum of this product is, in
7
analogue. Their b-functionalities enable their application in
sensing and molecular recognition. While the chemistry of
contrast to the porphyrin-like spectrum of porpholactone 4,
1
red-shifted and chlorin-like (Fig. 1). The H NMR spectrum
8
,9
3
,10
N-confused porphyrins is particularly rich,
the chemistry of
of 5 identifies four non-equivalent pyrrolidine b-protons
the longer known porpholactones 4 began to be explored only
1
more recently.
1,12
a
Department of Chemistry, University of Connecticut, Storrs,
CT 06269-3060, USA. E-mail: c.bruckner@uconn.edu;
Fax: +1 (860) 486-2981; Tel: +1 (860) 486-2743
Department of Chemistry, Youngstown State University,
One University Plaza, Youngstown, OH 44555-3663, USA
b
w Electronic supplementary information (ESI) available: Details of the
preparation of all novel compounds. CCDC 821398–821400. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c1cc12955d
z Oxazolochlorins 5. Oxazolochlorins 4: ref. 12
y Dedicated to Prof. Gerhard Bringmann on the occasion of his 60th
birthday.
Scheme 1 Reaction conditions: (i) B1 : 2 NH
D, 5 d. (ii) /SmI , o-Cl , D.
2
NH
2
ꢀ2H
2
O/THF (v/v),
2
2 6 4
C H
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Chem. Commun., 2011, 47, 8599–8601 8599

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Fig. 2 Stick representation of the single crystal X-ray structure of 6,
2
, and 8. All disorder, solvates and hydrogens bound to sp -carbons
7
removed for clarity. For details, see ESI.w
Fig. 1 UV-vis spectra of porpholactone 4, chlorolactone 5, and
porpholactam 8 (top) and N-aminoporpholactam 6 and N-amino-
2
the sp -hybridized b-carbon was linked to the porphyrin-like
chlorolactam 7 (bottom), all in neutralized CH
2 2
Cl .
1
1
spectrum of porpholactone 4, it does not surprise that the
O-to-N exchange retains the porphyrin-like spectrum. We will
refer to the 2-aza-3-oxo-porphyrin framework structure as
porpholactam, and to compound 6 as N-aminoporpholactam.
Product 7 proved to be the N-aminolactam analogue to
chlorolactone 5 (Fig. 2). The UV-vis spectrum of compound 7
is also chlorin-like, albeit somewhat (B10 nm) red-shifted
(Fig. 1). We name this framework chlorolactam. The origin
of this product from 5 can be confirmed by reaction of isolated
5 with hydrazine over the course of several days.
(
4.06–3.98 ppm), while the retention of the lactone moiety was
ꢁ
1
13
indicated in its IR (1757 cm ) and C NMR (170 ppm) spectra.
The absence of isomers of this novel chlorolactone and the
2
chemical shift similarity of the four sp b-protons suggest that a
reduction had taken place at the pyrrolic moiety opposite to the
oxazolone moiety. There is precedence for a hydrazine-induced
13
reduction of a porphyrin to a chlorin. Interestingly, product 5
is not accessible through a traditional diimide reduction of
14
porpholactone 4. Reflecting the structural and optical properties
of 5, we suggest to name this chromophore chlorolactone.
The compositions of the major products 6 and 7 are
suggestive of the takeup of hydrazine by porpholactone 4
and chlorolactone 5, respectively, with concomitant loss of
Hydrazine derivatives are susceptible to reductive N–N
1
6
cleavage using SmI
.
This reaction can also be applied to
2
N-aminolactam 6, generating the parent porpholactam 8,
though this reduction proceeds only at elevated temperatures
(o-dichlorobenzene, reflux, bp = 180.5 1C) (Scheme 1). Most
1
13
water. H and C NMR spectroscopic data of the products
were indecisive whether a hydrazone or an N-aminolactam
had formed, while IR spectroscopy supported the lactam
1
diagnostic in the H NMR spectrum of this compound is the
2
replacement of the signals assigned to the NH -group protons
ꢁ
1
ꢁ1
formulation (nCQO at 1686 cm and 1678 cm , respectively).
The definitive structural assignment of products 6 and 7 was
at 4.13 ppm in 6 by a signal at 9.64 ppm, assigned to the lactam
NH group. X-Ray diffractometry also confirms this trans-
formation (Fig. 2). Structurally porpholactam 8 is a hybrid
between porpholactone 4 and imidazoloporphyrin 3, or the
1
5
provided by single crystal diffractometry (Fig. 2).
The connectivity of 6 confirmed the presence of the
N-aminolactam moiety. As could be expected based on the
similar steric requirements of the imidizalone, oxazolone, and
pyrrole moieties, the replacement of the lactone by a lactam
moiety does not disturb the overall planarity of the system.
The replacement of a b,b-bond in 1 by a lactone (in 4) has
1
7
aza-analogue to 3-oxo-2-aza-21-carbachlorin 9.
5
minimal effects on its optical spectra. Likewise, the lactone-to-
lactam replacement has only minor effects (Fig. 1). Save
for a general minor bathochromic shift, the optical spectrum
of 6 is very similar to that of lactone 4. As the presence of
8
600 Chem. Commun., 2011, 47, 8599–8601
This journal is c The Royal Society of Chemistry 2011

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2
L. Latos-Grazynski, in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, San Diego, 2000,
pp. 361–416.
3
4
A. Srinivasan and H. Furuta, Acc. Chem. Res., 2005, 38,
1
0–20.
S. Kai, M. Suzuki and Y. Masaki, Tetrahedron Lett., 1998,
9, 4063–4066; J. Akhigbe, G. Peters, M. Zeller and C. Bruckner,
Org. Biomol. Chem., 2011, 9, 2306–2313.
M. J. Crossley and L. G. King, J. Chem. Soc., Chem. Commun.,
984, 920–922; M. Gouterman, R. J. Hall, G.-E. Khalil,
3
¨
5
1
P. C. Martin, E. G. Shankland and R. L. Cerny, J. Am. Chem.
Soc., 1989, 111, 3702–3707; K. Jayaraj, A. Gold, R. N. Austin,
L. M. Ball, J. Terner, D. Mandon, R. Weiss, J. Fischer, A. DeCian,
E. Bill, M. Mu
Chem., 1997, 36, 4555–4566.
J. R. McCarthy, H. A. Jenkins and C. Bru
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M. Pawlicki and L. Latos-Grazynski, J. Org. Chem., 2005, 70,
123–9130.
¨ ¨
ther, V. Schunemann and A. X. Trautwein, Inorg.
6
7
8
¨
ckner, Org. Lett., 2003,
5
Fig. 3 UV-vis spectra of N-aminoporpholactam 6 and porpholactam
in CH Cl /0.5% TFA.
8
2
2
9
M. Gouterman, J. Callis, L. Dalton, G. Khalil, Y. Mebarki,
K. R. Cooper and M. Grenier, Meas. Sci. Technol., 2004, 15,
The removal of the N-amino group from 6 causes only a
1
986–1994; G. E. Khalil, P. Daddario, K. S. F. Lau, S. Imtiaz,
M. King, M. Gouterman, A. Sidelev, N. Puran, M. Ghandehari
and C. Bruckner, Analyst, 2010, 135, 2125–2131.
9 Y. Xie, T. Morimoto and H. Furuta, Angew. Chem., Int. Ed., 2006,
5, 6907–6910.
0 H. Maeda and H. Furuta, Pure Appl. Chem., 2006, 78,
9–44.
1 C. Bru
minor (B2–3 nm) blue-shift of the UV-vis spectrum of the
resulting product 8 (Fig. 1). However, upon addition of acid,
the behavior of porpholactam 8 and its N-amino-derivative 6
vary significantly from each other. While protonation of 8
shows the expected behavior of porphyrins and porpholactones
¨
4
1
1
2
(
reduction of the number of side bands, hypsochromic shift
¨
ckner, J. R. McCarthy, H. W. Daniell, Z. D. Pendon,
of the Soret band, and a minor shift of lmax), protonation of
N-aminoporpholactam 6 results in a further red-shift and
intensification of the side bands (Fig. 3). We interpret this as
an indication that N-aminolactam 6 gets protonated at the
N-amino group and the inner nitrogen(s), whereas lactam 8 is
being protonated solely at the inner nitrogens.
R. P. Ilagan, T. M. Francis, L. Ren, R. R. Birge and
H. A. Frank, Chem. Phys., 2003, 294, 285–303.
1
1
2 J. Ogikubo and C. Bru
3 A. R. Genady and D. Gabel, Tetrahedron Lett., 2003, 44,
915–2917.
¨
ckner, Org. Lett., 2011, 13, 2380–2383.
2
1
4 The multiple products formed in the diimide reduction
(H. W. Whitlock Jr, R. Hanamer, M. Y. Oester and B. K. Bower,
J. Am. Chem. Soc., 1969, 91, 7485–7489.) of porpholactone 4 could
not be identified.
In conclusion, we have shown that it is possible, using a
step-wise approach, to replace a pyrrolic building block in
meso-tetraphenyl-porphyrin or -chlorin by an imidazolone
moiety. These are the first examples of a direct O-to-N exchange
in a pyrrole-modified porphyrin that amount to a formal
exchange of an oxazolone moiety by an imidazolone moiety.
1
30 6 2
5 Crystal structure data: (6) C43H N O, 0.37 (H O), M = 653.34,
˚
triclinic, a = 11.737(4), b = 12.257(4), c = 13.154(4) A,
3
˚
a = 76.707(4), b = 78.360(4), g = 65.649(4), V = 1665.6(9) A ,
T = 100 K, space group P 1% (no. 2), Z = 2, 12 566 reflections
measured, 5846 unique (Rint = 0.0474)—used in all calculations.
Final R value 0.0861, wR(F2) 0.2608 (all data). CCDC 821399 (7)
C43H32N O, 2(C H O), M = 740.88, triclinic, a = 11.805(2),
1
8
While g-lactams have been reported in benziporphodimethene,
calixphyrin, N-confused hexaphyrin, and N-confused
6
2
6
1
9
20
˚
b = 12.627(2), c = 13.460(2) A, a = 107.192(2), b = 95.593(2),
3
˚
%
9
,17
g = 90.383(3), V = 1906.2(6) A , T = 100 K, space group P1 (no. 2),
Z = 2, 25 313 reflections measured, 9008 unique (Rint
.0345)—used in all calculations. Final R value 0.0767, wR(F2)
0.1640 (all data). CCDC 821400 (8) C43 O, M = 631.71,
porphyrin (9),
they were established by means of (often
=
fortuitous) oxidations of a pyrrolic building block. This
lactone-to-lactam replacement does not dramatically alter
the UV-vis spectroscopic properties of the porpholactams.
This is also the first report of chlorolactones and chlorolactams.
The differing optical response of the N-aminolactams upon
protonation compared to lactones and regular porphyrins
provides a first glimpse of the potential of porpho- and
chlorolactams in, for instance, sensing applications.
0
29 5
H N
˚
triclinic, a = 6.3503(15), b =10.384(3), c = 12.353(3) A,
˚
3
a = 94.720(4), b = 99.884(4), g = 100.532(4), V = 783.5(3) A ,
T = 100 K, space group P 1% (no. 2), Z = 1, 8429 reflections
measured, 3844 unique (Rint = 0.0367)—used in all calculations.
Final R value 0.0564, wR(F2) 0.1591 (all data). CCDC 821398. For
further details, see ESIw.
1
2
6 For reviews of the use of SmI as reductant: D. B. G. Williams,
K. Blan and J. Caddy, Org. Prep. Proced. Int., 2001, 33, 565–602;
G. A. Molander, In Organic Reactions, ed. L. Paquette, Wiley,
New York, 1994, vol. 46, pp. 211–367.
Support from the NSF (CHE-0517782 and CMMI-0730826
to C.B.) is gratefully acknowledged. The diffractometer was
funded by NSF grant 0087210, Ohio Board of Regents grant
CAP-491, and by YSU.
1
1
1
7 I. Schmidt and T. L. P. J. Chmielewski, Tetrahedron, 2001, 42,
6
389–6392.
8 B. Ward, C. K. Chang and R. Young, J. Am. Chem. Soc., 1984,
06, 3943–3950.
1
Notes and references
9 H. Furuta, T. Ishizuka, A. Osuka, Y. Uwatoko and Y. Ishikawa,
Angew. Chem., Int. Ed., 2001, 40, 2323–2325.
1
The Porphyrin Handbook, Vol. 2-Heteroporphyrins, Expanded
Porphyrins and Related Macrocycles, ed. K. M. Kadish, K. M.
Smith and R. Guilard, Academic Press, San Diego, 2000.
20 A. Srinivasan, T. Ishizuka, A. Osuka and H. Furuta, J. Am. Chem.
Soc., 2003, 125, 878–879.
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 8599–8601 8601