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Intramolecular [4 + 4] Photocycloaddition of [2.

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BnoooAc
CHzOAc
CH2-Q
CH20Ac
HBr
N3
N3
(2a). R = H
(la), R = H
( l b ) , R = Bn
(2b). R = Bn
CHz-0
+
@
CHzOAc
AgClOi
BnO
BnO
N3
N3
N3
(5)
Bnowo
(3)
16 i
N3
(7)
R n = CHz-C,H5
according to known methods. Thus a pathway is now available
for selective synthesis of wglycosides of D-galactosamine.
Received: April 26, 1976 [Z 461 c IE]
German version: Angew. Chem. 88,478 (1976)
CAS Registry numbers:
( l a ) , 6893-59-0: ( 2 a ) , 59464-21-0: (261, 59464-22-1; ( 3 ) , 59464-23-2;
( 4 ) , 59464-24-3; ( 5 ) . 59464-25-4; (61, 55682-47-8; (7). 59464-26-5;
(8). 59464-27-6; 1.6-anhydro-P-o-galactose,
644-76-8;
benzyl alcohol, 100-51-6; tetraethylammonium chloride, 56-34-8
lecular excimer. Unlike (3)['1, which undergoes exclusive photochemical deactivation, it emits a very broad structureless
excimer fluorescence(cyc1ohexane:
;;:1 =416 nm; CjFI=0.O21;
acetonitrile: X".",':.=411 nm). Even at - 196°C (ether/
ethanol = 1 :2 ;[;:A
= 420 nm) it remains unstructured and is
far more intense than the phosphorescence of (I ) (
2
:
;
. = 527,
542, 549, 572, 592, 61 5 nm; T P =
~ 0.24 s)['].
H . Paulsen, 0 .Lockhuff, B. Schroder, B. Sumfleth, and W Srenzel, Tetrahedron Lett., in press.
R. Montgomery in W Piyman and D.Horron The Carbohydrates. Academic Press, New York 1970, Vol. IIB, p. 689.
A . Gottschalck: Glycoproteins. Elsevier, Amsterdam 1966.
R. U . Lemieux, K . James, and 7: L. Nagabushan, Can. J. Chem. 51,
42, 48 (1973).
H . Paulseri and W Stenzd, Angew. Chem. 87,547 (1975); Angew. Chem.
Int. Ed. Engl. 14. 558 (1975).
'
Intramolecular [4 +4]Photocycloaddition of [2.2](1,4)Naphthalenophane
By Gerd Kaupp and Inge ZimmermannC']
The twofold intramolecular Diels-Alder reaction occurring
on ten days' irradiation of anti-[2.2](1,4)naphthalenophane
(1) to form dibenzoequinene (2)['] is exceptional. The related
[2.2](9,10)anthracenophane (3) is known to undergo particularly smooth [4 +4]photocycloaddition to give (4)L21, and
numerous naphthalene derivatives suffer intermolecular
[4 + 4]photodimeri~ations[~].
Since the well-proved approach
of empirical conformational analysis with the aid of molecular
models[2.4l also suggest the [4 + 4lreaction to be more favorable geometrically than [4+2]addition in the case of ( I ) ,
we have examined the photodeactivation of (1) by spectroscopic and chemical methods and now report new findings
which confirm the predictions of conformational analysis.
Ethano bridges maintain the internal six-membered rings
of ( I ) [as in (3)]C21 in close proximity. Expectedly, a UV
spectrum is found [cyclohexane: A,, (E)= 238 (39000), 246
(37000), 273 (sh, 6200), 283 (sh, 5600), 302 (sh, SSOO), 310
(6000), 320 (sh, 4850), 327 (sh, 3700), 333 nm (sh, 2400)] which
extends to higher wavelengths (up to ca. 355nm) than that
of 1,4-dimethylnaphthalene['l.Electronically excited ( I ) must
accordingly be regarded, like (3), as an example of an intramo-
I*]
Doz. Dr. G. Kaupp and 1. Zimmermann
Chemisches Laboratorium der Universitat
Albertstrasse 21, 7800 Freiburg (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
[**I
Angew. Chem. lnr. Ed. Engl.
Vol. 15 (1976) No. 7
13)
(4)
Apart from luminescence, a diminution of the UV absorption with concomitant formation of the [4+4]product (5)
is observed on long-wave excitation (above 290nm).
Compound ( 5 ) is thermolabile. At room temperature it
undergoes extremely rapid rearomatization to regenerate ( 1 )
(tl,' = 76 s at 20°C). According to UV analysis this back-reaction is first-order when performed between - 15 and + 2 5 T
in toluene and has an activation energy of E, = 18.65kcal/mol
441
and a frequency factor A = lO"~"s-'.
Thus derivatization
must be performed at as low a temperature as possible. In
order to prepare (6) [m.p. 315°C (dec.)] compound ( I )
(200mg) is irradiated in toluene for 1 h (Philips HPK 125
W, Pyrex filter), then ozonized at -80°C with addition of
methanol and subjected to oxidative work-upr61.
The cyclic process ( I ) % ( 5 ) 4 ( 1 ) proceeds highly uniformly so that at temperatures above 20°C and on prolonged
irradiation the thermally more stable escape product (2) can
be formed (25 %; 10d; 16 fluorescent lamps)['], although there
is no conceivable conformer of ( 1 ) in which [4+2] reactions
giving (2) would be geometrically favored over the kinetically
preferred [4+4] reaction to form ( 5 ) .
Since the presumably [as for (3)
(4)]['l two-step formation of ( 5 ) must compete with relatively intense excimer
luminescence it would appear to be geometrically hindered.
Thus it must be assumed that the internal aromatic rings
of the conformers of (I) which absorb at longer wavelengths
are laterally displaced and not completely parallel to each
other. In this way excessive steric interactions are avoided
between aliphatic and peri H atoms, and photoreaction after
long-wave excitation can only occur subsequent to a slight
conformational change. A thermal activation threshold must
be overcome in the process, for the photochemical [4+4]
reaction of ( 1 ) to form ( 5 ) (313; 334 nm) is no longer observed
at - 190"C.-Excitation at shorter wavelengths leads to
[6+ 6)
Received: April 26, 1976 [Z 462a IE]
German version: Angew. Chem. 88,482 (1976)
CAS Registry numbers:
( I ) , 14724-91-5;(2), 15129-78-9;( 3 ) , 5672-91-9; ( 5 ) , 59473-41-t ; ( 6 ) , 5947348-2
[l] H . H . Wasserman and P . M. Keehn, J. Am. Chem. SOC.91, 2374 (1969);
89, 2770 (1967).
[2] G. Kaupp, Angew. Chem. 84, 259 (1972); Angew. Chem. Int. Ed. Engl.
11, 313 (1972); Justus Liebigs Ann. Chem. 1973, 844.
[3] W H. f. Sasse, 7: Teitei,and D . Wefls in Book of Contributed Papers,
[4]
[5]
[6]
[7]
poration of the conjugated double bonds in largely planar
rings['b]. We now report new photocleavages of the phanes
( I ), ( 3 ) , and (6) which confirm these arguments.
[2.2](2,5)Furanophane (1 )['I exists in the relatively rigid
step-type conformation, as shown by molecular models. Its
223
)=
(15000), 231 (sh,
UV spectrum [cyclohexane: ,I,,(&
10200),238 (sh, 2740), 246nm (sh, 1220)] permits excitation
with a low pressure mercury lamp. Irradiation (20 or - 190°C)
is seen to lead to a very rapid build-up of UV spectra corresponding to those of 2,5-dimethylene-2,5-dihydrofuran(2)['"1
which can be isolated at - 78 "C [ether/ethanol= 1 :2; 25 "C,
(Ere1)=232
1,,,=231 sh, 288sh, 296, 305sh; -190°C: i.,,,
(0.68),278 (sh, OSI), 290 (sh, 0.79),299.5 (1.00), 312nm (0.77)].
These spectra are stable for several hours at 25°C and also
survive brief irradiation with 31 3 nm light. No processes competing with [6 61 photocycloreversion of (1 ), such as fluorescence, can be observed (@F1<10-5);an isosbestic point is
registered at 229 nm.
+
Also in the case of [2.2]paracyclophane (3) conformational
conditions appear favorable for [6 61 photocleavage to give
p-quinodimethane (4). On the other hand, transannular interactions are apparent from the UV
The excimer
character of long-wave excited (3) is revealed also by an
unstructured fluorescence (cyclohexane: A:;=
355 nm, QFI=
0.0081)[4! Substantiation of these concepts comes from
the fluorescence of sterically fixed janusene ( 5 ) r 5 ] having two
parallel benzene rings separated by 2.5A. As for (3) it is
= 343 nm, QF,=0.0025; ether/
unstructured (cyclohexane:2;:
ethanol, - 196°C : 340 nm) and thus supplements observations
made for (6)[6].
+
Euchem Research Conference on Useful Preparative Aspects of Photochemistry, Ghent (Belgium) 1975.
G. Kaupp, lecture at Chemiedozententagung at Regensburg, April 2,
1976. The Woodward-Hoffmann Rules and Thereafter. Universitat Freiburg (Germany), 1974/75.
All the corrected excitation spectra are superposable on the UV spectra
above 270nrn (UV in ether/ethanol=l:2 at -190°C: 2,,,=236, 248,
273,282 sh, 304 sh, 314, 320 sh, 328, 333 sh).
R. Criegee, Angew. Chem. 87, 765 (1975); Angew. Chem. Int. Ed. Engl.
14, 745 (1975); the structure of (6) follows from the analytical and
spectroscopic data of the ester obtained with diazomethane,
G . Kaupp, Angew. Chem. 88, 482 (1976); Angew. Chem. Int. Ed. Engl.
IS. 442 (1976).
[6 + 61 Photocleavage of [Z.Z]Cyclophanes["]
By Gerd Kaupp[*]
Photochemical [6+ 61 reactions are of significance as higher
members of the cyclovinylogous series of two-step multicenter
Their success is tied to important conformational
conditions. Thus both unproductive radiationless deactivation
by conformational changes (such as internal rotation or inversion) and excessive competition from simpler reaction types
in smaller sections of the 12-electron system must be avoided.
With suitable [2.2]cyclophanes these conditions can be satisfied by restriction of the conformational flexibility and incor-
[*I Doz. Dr. G. Kaupp
Chemisches Laboratorium der Universitat
Albertstrasse 21, 1800 Freiburg (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
442
On long-waveexcitation of (3) (300,313 nm) no [6+6]cleavage to give ( 4 ) is observed. Only short-wave excitation leads
to [6 + 63 cycloreversion, albeit significantly more slowly than
in the case of (1 ). At - 190°C in ether/ethanol= 1 :2 this
reaction is manifested directly by the appearance of reproducible UV spectra of (4). The suspected two-step nature of
the reaction is confirmed above all by the structure of openchain alcohol adducts obtained from (3) at room temperatureL71.
The UV spectra of ( 4 ) which can now be conveniently
recorded lie at much longer wavelengths than those recorded
in the gas phase['"'. Nor do they possess the unstructured
bell shape, which has meanwhile been theoretically interpreted,
found from film spectra recorded after vacuum pyrolysis of
Anyew. Chrm. Inr. E d Engl.
/ Vol. 15. (1976) No.
7
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