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Synthesis of the First -Methylene--peroxylactoneЧRegiospecific Ene Reaction of 1O2 with -Unsaturated Carboxylic Acids.

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upon thermolysis of I , R = tBu,['] we were unable to isolate
a complex of type 2 . At 100"C, decarbonylation led to formation of the cluster 3.['l
21 1.2(3), Cr-P(diphospheneJ228.7(2)-232.4(2). Further details of the crystal structure investigation are available on request from the Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-7514 EggensteinLeopoldshafen 2, on quoting the depository number CSD-51546, the
names of the authors, and the full citation of the journal.
161 G. Huttner, G. Mohr, P. Friedrich, H. G. Schrnid, J . Organomer. Chem.
160 (1978) 59: G. Huttner, G. Mohr, P. Friedrich, Z. Naturforsch. 333
(1978) 1254.
[71 H. Vahrenkamp, D. Wolters, A n g e w . Chem. 95 (1983) 1 5 2 ; Angews. Chem.
Int. Ed. Engl. 22 (1983) 154: M. M. Olmstead, P. P. Power, J . Am. Chem.
Soc. 106 (1984) 1495.
[XI A. Albini, H. Kisch, J. Organomet. Chem. 94 (1975) 7 5 : P. Mastropasqua,
P. Lahuerta, K. Hildenbrand, H. Kisch, rhrd. 172 (1979) 57; H. Kisch, C.
Kriiger, A. Trautwein, Z. Naturforseh. 8 3 6 (1981) 205; G. Fischer, G .
Sedelmeier, H. Prinzbach, K. Knoll, P. Wilharm, G. Huttner, 1. Jibril, J.
Organornet. Chem.. in press.
Synthesis of the First a-Methylene-p-peroxylactoneRegiospecific Ene Reaction of 'OZwith
a$-Unsaturated Carboxylic Acids**
By Waldemar Adam* and Axel Griesbeck
3 is the second example of a triangulo-trichromium cluster"] whose structure has been confirmed by X-ray analysis."] It contains a p3-PR bridge, which hitherto has only
been observed in clusters containing at least two metals of
the eighth subgroup.['] 3 is the first example of a cluster
containing a Z-diphosphene moiety RP=PR as side-on
and end-on coordinated ligand.
Whereas diphosphenes have already been observed as
building blocks of complexes with metal-metal bonds in
other types of coordination,['] the type of bonding found
for 3 was hitherto unknown. It corresponds to a mode of
coordination of 2-diazenes in clusters['] and thus substantiates the analogy between the bonding in R N = N R and
Received: August 5 , 1985 [Z 1414 IE]
German version: Angew. Chem. 97 (1985) 1069
CAS-Registry-numbers :
1, 90443-62-2; 3, 99034-13-6; P, 7723-14-0; Cr, 7440-47-3.
[I] H. Behrens, W. Haag, Chem. Ber. 94 (1961) 320; M. Hoefer, K.-F. Tebbe,
H. Veit, N . E. Weiler, J . Am. Chem. Soc. I05 (1983) 6338; D. J. Darensbourg, D. J. Zalewski, OrganometaNics 3 (1984) 1598.
121 G. Huttner, J. Borm. L. Zsolnai, J. Organomet. Chem. 263 (1984) C33.
131 J. Borm, L. Zsolnai, G. Huttner, Angew. Chem. 95 (1983) 1018; Angew.
Chem. Int. Ed. Engl. 22 (1983) 971; Angew. Chem. Suppl. 1983. 1477.
[4] 1 (200mg, 0.42 mmol), R=tBu 121, was melted at 100°C. Within 30 rnin
the melt turned brown in color and Cr(CO)6 sublimed off. The brown
residue was dissolved in CH2C12( 5 mL), treated with silica gel (1 g), and
evaporated to dryness. Chromatography o n silica gel (30°C; 15 x 2.5 cm)
with n-pentane/CH2C12 ( I : I ) furnished an orange-brown zone from
which 3 was separated from a yellow, still unidentified byproduct by
fractional crystallization in the form of brown crystals. 3 is also slowly
formed from crystalline 1 upon storage at 20°C for several months.
Yield: 20 mg of 3 (20% based on 1); correct elemental analysis. IR (npentane): v=2034 (w), 1983 (vs), 1968 (s), 1955 (m), 1946 (w), 1836 (w).
' H NMR (CDCI,): fi= 1.74 (pseudotriplet, 'J(PH)= 10 Hz, I8 H); 2.46 (d,
'J(P€f)= 19 Hz, 9 H ) . " P / ' H J NMR (CHZCIZ): 6=352 (s, 2P); 659 ( s , I P).
MS: m / i 700 (%), 672 ( I ) , 644 (3), 616 ( I ) , 588 (3), 560 (7), 532 ( 3 ) , 504
(lo), 476 (S), 448 ( S ) , 420 ( S ) , 392 (2), 364 (6), 336 ( I ) , 308 (20), 251
( M + - I O CO-Ru, 32). 137 ( M + - I 0 CO-3 Bu, 3), 57 (Bu', 60). 52
(Cr*. lo), 41 ( f , H : , 100). 39 (C%H:, 51). 3 is stable up to 250°C in the
wlid atate.
[ S ] P?,/c. Z = 4 , p',,,' = 1.62 g cm-', a = 1648.5(7), b=924.8(3), c = 1888.9(7)
pm: V=2879x 10" pm', ,u(MoKa)= 13.8 crn- I , T=20"C, 2856 independent reflections (1>2a(O), R , =0.051, R,=0.054. Important bond
lengths [pm]: Cr-Cr 281.4(2)-285.1(2), Cr-p3-P 224.0(2)-230.1(2), P-P
0 V C H Verlagsgesellschaji m b H , 0-6940 Weinheim, I985
Alkyl-substituted p-peroxylactones have long been
known,"-'] and their behavior upon thermolysis and upon
direct or triplet-sensitized photolysis has been investigated
in detail.l4I We report here on an entry to 5-methyl-4-methylene 1,2-dioxolan-3-one 4, the first u-methylene-p-peroxylactone. The key step of the synthesis is the regiospecific photooxygenation of an a,D-unsaturated carboxylic
acid (Scheme I).
Scheme I
Irradiation (A: 150-W sodium lamp, unfiltered) of a solution of tiglic acid l in CCI, (concentration: 0.25 mol/L)
in the presence of traces of tetraphenylporphine at 10°C
affords the allylic hydroperoxide 2 (yield: 92%). The isomeric ene product is not formed. 2 can also be synthesized
by photooxygenation of angelic acid 3, but three- to fourfold longer reaction times are required.
This 'O,-reaction is remarkable, for two reasons: a) as
shown by competition experiments,"] the addition of a carboxyl group in 2-butene does not lead to appreciable diminution in the reactivity, i.e. trans-2-butene reacts only ca.
twice as fast as tiglic acid 1 with '0'; b) both the ene reaction of 1 as well as that of 3 proceed regiospecifically to
give the 0-hydroperoxy-a-methylenecarboxylic
acid 2 .
Acid-catalyzed dehydration with H2S04 in CHC& at
0°C affords the a-methylene-p-peroxylactone 4, which can
Prof. Dr. W. Adam, Dr. A. Griesbeck
Institut fur Organische Chemie der Universitat
Am Hubland, D-8700 Wiirzburg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft
(Sonderforschungsbereich No. 172 "Molekulare Mechanismen kanzerogener Primarveranderungen"), the Stiftung Volkswagenwerk, and the
Fonds der Chemischen Industrie.
0570-0833/85/12/2-1070 $ 02.50/0
Angew. Chem. In/. Ed. Engl. 24 (1985) No. I 2
be isolated in 61% yield by short-path distillation at 3236"C/0.08 torr as a colorless oil having an unpleasant
odor. 4 gives with potssium iodide a distinct peroxide spot
on the thin-layer chromatogram (R,= 0.70; S O z , CH2CIZ).
The titrimetrically determined peroxide content amounted
to 27.65"O (calc. 28.04%), corresponding to a purity of
9 8.6%.
[ I ] F. D. Greene, W. Adam. G. A. Knudsen, J . Org. Chem. 31 (1966) 2087.
[2] W. Adam, C . I. Rojas, Syn/hesis 1972. 616.
131 W. Adam, Acr. Chern. Res. 12 (1979) 390.
[4] W. Adam, 0. Cueto, L. N. Guedes, J. A m . Chem. Soc. 102 (1980) 2106.
[ S ] k(cis-2-butene)/k(l) = 8.0; k(trans-2-butene)/k(3) =7.7; k( l ) / k ( 3 ) =3.8
(in CCI, at 10°C).
[6] W. G. Dauben, L. Salem, N. J. Turro, Arc. Chrm. Res. 8 (1975) 41.
Table I . ' H dnd "C-NMR data and selected IR data of 2 and 4.
Sensitized UV/Laser Photolysis of Azoalkanes:
Conformational Influences on Intersystem-Crossing
and Lifetimes of Triplet Diradicals**
1.38 (d, 3 H , J = 6 . 2 Hz)
(li values) [a]
4.95 (4,I H, J=6.2 Hz)
6.02 (s, I H)
6.48 (s, I H )
9.67 (br. s, 2 H)
values) [a]
IR [cm
18.34 (4)
79.13 (d)
128.32 (t)
139.91 (s)
171.90 (s)
3300 (s), 2990 (m),
1700 (s), 1628 (m),
I272 (m), I178 (m)
1.83 (d, 3 H , J = 6 Hz)
5.42 (ddd, H,, ' J = 6 Hz,
Jh,=2.8 Hz, J,%,=3.0 Hz)
5.77 (dd, Hh, Jh,,=0.7S Hz,
J,,=2.S Hz)
6.30 (dd, H,,, J,,,=O.75 Hz,
J.,,'= 3.0 Hz)
17.76 (4)
81.27 (d)
122.11 (t)
138.66 (5)
168.48 (s)
2990 (w). 1790 (s),
1672 (w), 1410 (s),
1246 (s), 1132 (s)
[a] 400 MHz, CDCI,, S values referred to TMS. [b] Film (NaCI plates). [c]
Correct elemental analyses. [d] Molecular weight: experimental, 116 (osmometric): theoretical, 114.
A comparison of the IR and of the ' H - and I3C-NMR
data of 2 and 4 (Table 1) lends support to the proposed
structures. A striking feature of the 'H-NMR spectrum of
4 is the additional 4JHH-couphg between H, and H, and
between H h and H,, which d o not occur in the open-chain
compound 2. 4 can be stored without deterioration at
-2O"C, but on heating to 70-80°C it undergoes complete
4 proves to be exceptionally stable upon flash photolysis: Even on passage through a quartz tube (60-cm long,
14-mm diameter, unpacked) heated to 1000°C at 0.08 torr
only 15"'o of the substance polymerizes; 85% thereof can be
recovered in the cold trap. This finding can be explained in
terms of the diradical state 5,16]which is proposed as intermediate.
By Waldemar Adam,* Klaus Hannemann, and
R . Marshall Wilson
Dedicated to Professor Rolf Huisgen on the occasion of
his 65th birthday
The importance of diradicals in chemical reactions is reflected in the large number of studies devoted to the detection and determination of the lifetime of these short-lived
intermediates."] Although their behavior is qualitatively
well understood,['] experimental data essential for testing
theoretical models are still greatly lacking. For example,
the law of conservation of total angular momentum for triplet-singlet intersystem-crossing requires a conformational
arrangement of the radical orbitals in which the radical orbital axes are oriented orthogonally to one another and
also to the axis about which the orbital angular momentum
is generated (Fig. la). In contrast, a parallel arrangement
(Fig. lb) of the radical orbitals proves to be unfavorable
for spin-orbital coupling.['l To our knowledge no experimental evidence has hitherto been put forward in support
of this theoretical prediction. Either the geometrical prerequisites are not given or the diradical is so strongly perturbed by substituents that no influences of the conformation on intersystem-crossing and, thus, on the lifetime of
the triplet diradical, can be recognized."'
Fig. I . Optimal orthogonal (a) and unfavorable parallel (b) arrangements of
the radical orbital axes for intersystem-crossing in triplet diradicals.
0 -5
Since the relative energies of TI-5and 0-5 are unknown,
it is impossible to make any definite statement about the
electronic nature of the diradical. Decarboxylation of TI-5
should lead to a n,n*-excited C02-molecule-an energetically very expensive fragmentation path. The cleavage of
C 0 2 from 0 - 5 would lead to a vinyl radical or, at least,
require a concomitant 1,2-methyl shift to an olefinic Catom, both of which are unfavorable for stereoelectronic
Received: August 8. 1988;
supplemented: October I , 1988 [Z 1416 IE]
German version: Angew. Chem. 97 (1988) 1071
Anqew. Chrm. Inr. Ed. Engl. 24 (1985) No. 12
Using the localized diradicals 1,3-cyclopentadiyl l a , 1,4cyclohexadiyl l b , and 2,7-bicyclo[2.2. Ilheptadiyl l c ,
which are not perturbed by substituents, as examples, we
show that the arrangement of the radical orbitals considerably influences the lifetimes of these transient speciesthey differ by more than four orders of magnitude. The di[*I
Prof. Dr. W. Adam, Dr. K . Hannemann
lnstitut fur Organische Chemie der Universitat
Am Hubland, D-8700 Wiirzburg (FRG)
Prof. Dr. R. M. Wilson
Department of Chemistry, University of Cincinnati
Cincinnati, OH 48221 (USA)
This work was supported by the Deutsche Forschungsgemeinschaft, the
Fonds der Chemischen Industrie, the National Science Foundation
(USA), and the North Atlantic Treaty Organization.
0 VCH Verlagsgesellschaft mbH. 0-6940 Weinherm. I985
0570-0833/85/1212-1071 !$ 02.50/0
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acid, synthesis, methylene, reaction, first, 1o2, peroxylactoneчregiospecific, carboxylic, ene, unsaturated
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