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Dependence of Anomeric Stabilization on Structure in Acetals.

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The equatorial C O ligands of the two Re(CO), groups are
staggered and as in Re,(CO),o,[161 12,['71and 13,"'I are bent
towards each other.
[(OC),Re-CH ,CH
,-Re(CO),]
[(OC),Re-C= C-Re(CO),]
Dependence of Anomeric Stabilization
on Structure in Acetals**
By Hans-Dieter Beckhaus, Barbara Dogan, Sergej Verevkin,
Johannes Hadrich, and Christoph Riichardt *
12
Dedicated to Paul vnn Rag& Schleyer on the occasion of his
60th birthday
13
Experimental
All operations were carried out in anhydrous solvent under nitrogen
7: A clear orange-colored solution (20'C) of Na[Re(CO),] (prepared from
185 mg (0.285 mmol) of Re,(CO),, and sodium amalgam in 5 mL of THF) was
added with stirring to the violet suspension of 6 [l I ] (150.3 mg, 0.2 mmol) in
l O m L of T H F (-78'C). After 1 h at -78 C, the mixture was warmed to
30 C. stirred for a further 60 min, and the solvent removed in vacuo. The
residue was taken up in CH,CI,, centrifuged, and the solvent again removed in
vdcuo. Subsequent washing of the residue with hexane (three times) and cold
MeOH (once) followed by drying in vacua furnished 7 as a reddish-brown
Crystals from CH,Cl,/hexane.
powder. Yield. 135 mg (51 YO).
IR(KBr): a[cm-'] = 3050- 3020 (w. CH); 2104(m). 2053(m). 2005(s), 1975(s)
(CO): 1595 (m. C = C ) . IR(CH,CI,): vCO[Re(CO),] = 2109 (m, A , ) , 2003 (s.
E). 1970 (s, A , ) ; vCO[Re(CO),] = 2054 (s. E).-'H N M R (270 MHz: CDCI,,
25 C. CDCI, a s standard): 6 = 7.73 (m, 12H). 8 11, 8.36 (m. 8H); 8.86 (s,
8H). -I3C NMR (67.89 MHz; CDCI,, 25 C, CDCI, as standard). d = 120.8,
121.8, 126.8. 127.7, 132.1. 133.6, 141.7, 145.6 (TPP), 178.9 (CO): 211.7 (Carbene-C)
The anomeric effect"] is a well known example of a synergetic interaction of geminal substituents on a saturated
carbon atom. According to this concept the two alkoxy
groups in acetals 1 contribute more to the stabilization of the
molecule than would correspond to a purely additive effect.[''] Although this extra stabilization is thought to be
responsible for a number of phenomena, e.g. the conformational preference and reactivity of glucosides,"'] very few
quantitative experimental data are available[**31 on the
extent of anomeric stabilization and its variation by substituents on the anomeric carbon atom. The generally accepted model [ I d 1 of "negative hyperconjugation" suggests
that alkyl and aryl residues on the central C-atom could alter
the anomeric stabilization.
Received: October 20, 1989 [Z 3598 IE]
German version. Angen. Chem. I02 (1990) 331
Ph,
,ORZ
P
Rl/L'OR3
[I] Review: W. A. Herrmann, A n g m . Chem. 98(1986)57; Angeic. Chem. I n t .
Ed. Engl. 25 (1986) 56.
[2] a) D. Mansuy, J:P. Lecomte, J:C. Chottard, J.-F. Bartoli, Inorg. Chem. 20
(1981) 3119, b) V. L. Goedken. M. R. Deakm, L. A. Bottomley, J. Chem.
Soc. Chem. Commun. 1982,607;c) D. R English, D. N. Henrickson, K. S.
Suslick, Inorg. Chem. 22 (1983) 367.
[3] G. Rossi, V. L. Goedken, C. Ercokani. J Chem. Soc. Chem. Commun. 1988,
46; E N. Bakshi, C. D. Delfs, K. S. Murray. B. Peters, H. Homborg,
h o g . Chem. 27 (1988) 4318;
[4] S. L. Latesky. J. P. Selegue, J. Am. Chem. Soc. I09 (1987) 4731.
[5] R. J. Blau. M. H. Chisholm, K. Folting. R. J Wang, J. Am. Chem. SOC.109
(1987) 4552.
161 C. Zybill. D. L. Wilkinson. G. Muller, Angeiv. Chem. I00 (1988) 574;
Angeiv. Chum. I n / . Ed. Engl. 27 (1988) 583.
[7] W. Gide. E Weiss. J Orgunomel. Chrm. 213 (1981) 451; D . Melzer, E.
Weiss. ihrd. 263 (1984) 67; J. D. Korp. I. Bernal, R. Horlein, R. Serrano,
W. A. Herrmann, Chem. Bur. 118 (1985) 340; W. A. Herrmann, H.-J.
Kneuper, E. Herdtweck, ibid 122 (1989) 433.
[X] W. A. Herrmann, H:J. Kneuper, E. Herdtweck, Chem Ber. 122 (1989)
437.
191 W. A. Herrmann, H.-J. Kneuper. E. Herdtweck, Angew. Chem. 97 (1985)
1060; Angun. Chum. In!. Ed. Engl. 24 (1985) 1062; Chem. Ber. 122 (1989)
445.
1101 Review: W. Beck, Polyhrdron 7 (1988) 2255; W. Beck, B. Niemer, J. Breimair, J. Heidrich, J Orgunornet. Cl~em.372 (1989) 79.
[ l l ] D. Mansuy, M. Lange, I-C. Chottard, P. Guerin, P. Morliere. D. Brault,
M. Rougee. J Chum. Soc. Chem. Commun. 1977, 648; D. Mansuy, M.
Lange, JLC. Chottard. J. F. Bartoli, B. Chewier, R. Weiss. Angew. Chem.
90(1978)828; A n g e x Chem. I n t . Ed. EngI. 17(1978)781;D. Mansuy, Pure
Appl. Cliem. 52 (1980) 681; review on dihalocarbene complexes: P. J.
Brothers. W. R. Roper. Chem. Rev. 88 (1988) 1293.
[12] Compound 6 was also allowed to react with the cdrbonyhnetalates Mn(CO)?, Fe(C0):' and Cr(C0):'. The manganesecompound can, according to the IR spectrum [vCO[cm-'] (CH,CI,): 209S(m), 2033(s), 2004(s),
1970(m)]. be assigned a structure analogous to 7. Analytical and IR
data of the products obtained from 6 and Fe(C0):' and Cr(C0):O are
consistent with the formation of (TPP)Fe=C= Fe(CO), and
(TPP)Fe= C = Cr(CO),. respectively
[13] H Fischer. P. Hofmann, F. R. Kreissl. R. R. Schrock, U. Schubert. K.
Weiss: Curhvne Compkres. VCH Verlagsgesellschaft. Weinheim 1988.
[14] U. Schubert, K. Ackermann, P. Rustemeyer, J. Orgunornet. Chrm. 231
(1982) 323.
[IS] W A. Herrmann, R. A Fischer, E. Herdtweck. Angen. Cliem. 99 (1987)
1286: Angeiv. Chem. Inr. Ed. Engl. 26 (1987) 1263.
[16] L. F. Dahl. E. Ishishi, R. E. Rundle, J. Chem. Phy.s. 26 (1957) 1750; M. R.
Churchill. K . N. Amoh. H. J. Wasserman, Inorg. Chem. 20 (1981) 1609.
[I71 K. Raab, U. Nagel, W. Beck, 2. Na8uforsc-h. B3R (1983) 1466.
[la] J. Heidrich, M. Steimann, M. Appel, W. Beck, J. R. Phillips, W. C. Trogler.
Orgunonwtollics. in press.
320
g.2 VCH Verliigsg~~sellsc./Infr
mhH. 0-6940 Wurnheim. 1990
la:
1b:
lc:
Id:
R'
Ri
=
H, R 2 = R 3 = M e
=
RZ = R 3 = M e
R' = H, RZ, R 3 = -CHzCHzR ' = M e , RZ,R 3 = -CH,CH,l e : R i = H , RZ, R 3 = - C H z C M e z C H z I f : R 1 = Me, R 2 , R 3 = - C H z C M e , C H 2 -
We report here on thermochemical measurements with the
aromatic acetals 1a-f. The standard enthalpies of formation
AH! (g) were obtained from the enthalpies of combustion
AHc(1) and vaporization
(Table 1). The results of earlier measurements on aliphatic acetalsr3] were used in the
calculations.
We determined the extra, anomeric stabilization by comparison of the increments in enthalpy of formation of alkyl
and alkoxy groups with acetal groups. That is, we did not use
the enthalpy of formation of an individual compound in the
otherwise usual process of the isodesmic reaction,[51 but
group increments,"' which were calculated from several homologous structures. The result then has a broader experimental basis. We used the known increments AHalky,for alkanesL6"]and alkylbenzenes [6b1 (Table 2) and determined the
remaining increments according to the least squares method.
Firstly, the increments for the alkoxy groups AH,,, were
calculated from the A H : (8) values of dialkyl ethers. ['I The
division into the ether group 0 [2C] and the groups with C as
key atom and an 0 atom as neighbor CH, [O,C], C H [0,2C],
and C[O,3C] was done by defining the methyl group:
AHP(g) of CH,[O] = AHP(g) of CH,[C] = -10.05 kcal
mol-'. Finally, the increments for the alkyl groups with two
[*] Prof. Dr. C. Ruchardt, Dr. H.-D. Beckhaus, Dr. B. Dogan, Dr. J. Hidrich
Institut fur Organische Chemie und Biochemie der Universitat
Albertstrdsse 21, D-7800 Freiburg (FRG)
Dr. S. Verevkin
Kuibyshew Politechnisches Institut, Kuibyschew (UdSSR)
[**I Geminal Substituent Effects, Part 2. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. S.V. thanks the Deutscher Akademischer Austauschdienst (DAAD)
for an exchange grant.-Part 1 . [4c]
0570-0833/9010303-0320 $O2.S0/0
Angew. Chem. I n / . Ed. EngI. 29 (1990) No. 3
Table 1. Combustion enthalpies AHc(]),vaporization enthalpies AHvand standard enthalpies of formation AH? of la-f, as well as calculated values from
group increments AHc,ca,c6
[kcalmol-'1.
la
lb
Ic
Id
le
If
-1176.42
- 0.39
-1328.31
f 0.42
-1120.26
i0.33
-1267.03
i0.53
+
-1578.90
f 0.30
-1733.76
f 0.55
14.21
i0.17
13.15
k0.30
15.72
k0.23
19.57
f0.12
16.04
i0.19
13.63
k0.28
-79.93
k0.39
-90.41
f042
-67.77
k0.33
-83.37
k0.53
-91.79 [d]
i0.30
-103.74
i0.55
-65.72
i0.42
-77.26
i0.52
-52.05
k0.39
-63.80
k0.54
-75.75
f0.36
-90.11
f0.62
-64.62
1.10
-76.94
0.32
-52.92
-0.87
-65.24
-1.44
-76.32
-0.57
-88.64
1.47
[a] Group increments, see Table 2. [b] Ring strain (7.5 kcalmol-' in the case of
dioxacyclopentane, 2.5 in the case of all other oxacycles) and repulsion of
geminal methyl groups at the quaternary C-atom (2.0 kcalmol-I) were
- AHP(g).
taken into consideration as additive terms. [c] AAH = AHr.calcd
[d] AH, = 4.44.
0-atoms as neighbors (AHdioxy)
were calculated from the enthalpies of formation of the acetals (Table I).['] The goodness of fit is seen from the small differences AAH (see
Table 1 ) between the calculated value AHrqcalcd,
i.e. the sum
of the increments including the strain enthalpy, and AHP(g).
The increments AH,,, for a-CH,, a-CH and a-C atoms in
ethers are clearly smaller than the corresponding AHalky,
values in alkanes (Table2). Since we have allotted the same
Table 2. Increments in enthalpy of formation [kcalmol-'1 for alkyl (AH,,,,,),
alkoxy (AH,,,) and acetal groups (AHd,J [8].
AH,^^^^ PI
AH^^^ 171
AH,,,,,
aliphatic [8]
aromatic [b]
~~~~~
CH,
CH,
CH
C
[C] - 10.05
[2C] -5.13
[3C] -2.16
[4C] -0.30
[O]= - 10.05
[O,C] -8.0
[ 2 0 ] -14.1
[0,2C] -6.3
[ 2 0 , C] -15.6
[0,3C] -4.7 [ 2 0 , 2C] -17.9
-
-
[ 2 0 , C,,]
-18.9
[ 2 0 , C, CpJ -21.2
[a] Neighboring atoms of CH, in square brackets; C,, signifies phenyl-C atom
and C an sp'-C-atom. [b] From the acetals of Table 1.
values to the methyl groups CH,[O] as to the CH,[C]
groups, it follows that C atoms are more strongly stabilized
by a neighboring C-atom. The extent of this stabilization corresponds to the differences AH,,, - AHalkyl
and
AHdioxy
- AH,,, (Table 3). In ethers, this oxygen effect is similar for all groups (AHoxy- AHalkyl
= -2.8 to -4.4 kcal
mol-I). The stabilization on going from the ether to the
acetal, on the other hand, strongly depends on the degree of
substitution of the C-atom; AHdioxy
- AH,,, varies from
-6.1 to -16.5 kcalmol-'.
The extra, anomeric stabilization AAH,,,,,, , i.e. the additional energy gained on introduction of the second oxygen
atom in comparison to the first is given by the difference
(AHdloxy
- AH,,,,) - (AHoxy
- AH,,,,,) (Table 3). Aliphatic
acetals containing the C [20,2C] group are stabilized by
AAH,,,,,, = - 8.8, aliphatic acetals containing the
CH [2O,C]group by - 5.1, and formaldehyde acetals by only
-3.3 kcal mol-'. The anomeric effect increases by 2-4 kcal
mol-' on substitution of the anomeric carbon atom by an
Angen. Chem. I n t . Ed. Engl. 29 (1990) No. 3
0 VCH
alkyl. On replacing an alkyl group by a phenyl group with
the ability to undergo K conjugation the molecule is stabilized by a further 3.3 kcalmol-'. The acetal of an alkyl
phenyl ketone containing the C [2O,C,C,,] group exhibits
Table 3. Anomeric stabilization AAH,,,,.,
of aliphatic and aromatic acetals
from the difference in group increments (cf. Table 2) [kcal mol- '1
AH,,, [a1
- AH,,,,, [cl
C,, present [el
CH,[O,, C, .I
CH[O,, C3.J
C P , , C4-XI
-2.8
-4.2
-4.4
AHdioxy [bl
- AH,,, la1
no
-6.1
-9.3
-13.2
Yes
AAH,,,,,
[dl
no
yes
- 3.3
-12.6
-16.5
-5.1
-8.8
-8.4
-12.1
[a] Number of neighboring 0 atoms x = 1. [b] Number of neighboring 0 atoms
=
x = 2. [c] Number of neighboring 0 atoms x = 0. [d] AAH,,,,,
(AH,,,,, - AH,,,) - (AHaxy- AH,,,,,). [el To differentiate the pure aliphatic
acetals with CH,[2O,C, .,I
groups from aromatic compounds with
CH,[2O,CI -,C,,] groups.
the highest anomeric stabilization (- 12.1 kcal mol- ') detected so far. Current investigations should show whether a
further phenyl group (in benzophenone acetals) would increase the anomeric effect further, and whether an analogous
phenyl effect is effective in benzyl ethers."'
Received: October 26, 1989 [Z 3611 IE]
German version: Angew. Chem. 102 (1990) 313
CAS Registry numbers:
la. 1125-88-8; lb, 4316-35-2; lc, 936-51-6; Id, 3674-77-9; le, 776-88-5; If,
5406-58-6.
[l] a) A. J. Kirby: The Anomeric Effect and Related Stereoelectronic Effects at
Oxygen, Springer, Berlin 1983, and references cited therein; b) R. W.
Franck, Tetrahedron 39 (1983) 3251; c) P. von R. Schleyer, E. D. Jemmis,
G. W. Spitznagel, J. Am. Chem. Soc. I07 (1985) 6393; d) P. von R. Schleyer,
A. J. Kos, Tetrahedron 39 (1983) 1141; e) H.-G. Korth, R. Sustmann, K . S .
Groninger, M. Leisung, B. Giese, .
IOrg. Chem. 53 (1988) 4364.
[2] S. W. Benson: Thermochemical Kinetics, Wiley, New York 1976. p. 274.
[3] a) J. B. Pedley, R. D. Naylor, S. P. Kirby: ThermochemicaIDataqfOrgunic
Compounds, Chapman and Hall, London 1986; b) J. D. Cox, G. Pilcher.
Thermochemistry of Organic and Organometallic Compounds, Academic
Press, London 1970.
[4] a) Synthesis of 1 a-f: J. Hadrich, Dissertation, Universitat Freiburg 1989; b)
combustion in a Lund isoperibolic calorimeter: S . Sunner, M. Manson:
Combustion Calorrmetry. Vol. I , Pergamon Press, Oxford 1979; c) measurement of the enthalpy of vaporization: K. Fritzsche, B. Dogan, H.-D. Beckhaus, C. Riichardt, Thermochim. Acta, in press.
I
Am. Chem. SOC.92
[5] a) W. J. Hehre, R. Ditchfield, L. Radom, J. A. Pople, .
(1970) 4796; b) P. George, M. Trachtman, A. M. Brett, C. W. Bock, J. Chem
SOC.Perkin Trans. 2 1977, 1036.
I
Am Chem. Sot. 92
[6] a) P. von R. Schleyer, J. E. Williams, K. P. Blanchard, .
(1970) 2377; b) H.-D. Beckhaus, Chem. Ber. 116 (1983) 86.
[7] The AHP(g) values[3] ofthefollowingalkylethersenter into thecalculation
of the group increments AH,,, (Table 2): methoxymethane, l-methoxyethane, 1-methoxypropane, I-methoxybutane, 2-methoxypropane. 2-methoxy-2-methylpropane (1.4 kcal mol- l ) , I-ethoxyethane. l-ethoxypropane, di-n-propyl ether, diisopropyl ether (0.5). di-n-butyl ether, diisobutylether (0.5) and di-tert-butyl ether (6.6). The respective steric strains
taken into account in the calculations are quoted in brackets. They were
determined from the structurally analogous alkanes, obtained by replacing
0 by CH,. 0[2C] = -23.8 kcalmol-'.
181 The group increments for aliphatic acetals in Table 2 were derived from
1,3-dioxolane (AH?(g) = -71.10 kcalmol-'), 1Jdioxane (-80.86)
(- 111.32),
1,3,5-trioxacyclohexane
(- 148.24), 1,3,5,7,9-pentaoxacyclodecane(- 186.38). 2-methoxytetrdhydropyran (-95.50). dimethoxymethane (- 83 27). 1,l-dimethoxyethane
(-93 26), 2.2-dimethoxypropane (- 101.89), diethoxymethane (-99.14),
1,l-diethoxyethane (- 108.39), 2,2-diethoxypropane (- 121.08), and
dibutoxymethane ( - 119.81) [3]
[9] AHP(g) values for alkyl benzyl and dibenzyl ethers have not yet been listed
[31.
Verlagsgesellschajt mbH, 0-6940 Wemheim. 1990
0570-ORUiSOj0303-0321 S 02.5010
321
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