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In-Situ Blocking of an Aldehyde Function by Formation of (-Triphenylphosphoniumalkoxy)-titanium or -niobium Complexes.

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was also achieved in competition reactions of 5-7 with the
substrate pair heptanal/3-pentanone. In non-competition
experiments acetophenone could be dichloromethylated in
good yields with 5-7; but only at 0°C however in the case
of 5 (enolate formation at -78°C).
Grouping
The reagents 5-7 dichloromethylate the a-dimethylaminoketone 11 completely grouping
selectively in the presence of 3-pentanones (Scheme 3,
Table 3), whereas the lithium compound reacts unselectively.
In contrast to 13 and the products of type 9 and 10 obtained according to Scheme 2, 12 has, to our knowledge,
thus far never been described. Spectroscopic data for this
oily, readily decomposable substance, which could not be
obtained in analytically pure form, are listed in Table 4.
In-Situ Blocking of an Aldehyde Function by
Formation of (wTriphenylphosphoniuma1koxy)titanium or -niobium Complexes**
By Thomas Kauffmann,* Thomas Abel, and
Martin Schreer
Investigations of the influence of electron donor compounds on the nucleophilicity of [MeTiC13] 1 toward aldehydes and ketones revealed that the nucleophilicity decreases as shown in Scheme 1,’2,31 i.e. the circumstances are
the reverse to those observed in the case of lithium com-
[MeTiCI,] 1 in CH,C12, Et20, THF, DME, TMEDA
--t decreasing nucleophilicity
AlkylLi in
TMEDA, DME, THF, Et20, C6H12
Table 4. Spectroscopic data of 12
‘H-NMR (300 MHz, CDCI,, TMS): 6 = 1.65 ( s , 3 H ; CCH,), 2.34 ( s , 6 H ;
NCH,), 2.38 (d, 1 H ; CHH), 2.75 (d, I H ; CHH), 5.70 (s, 1 H ; CHCJ2); O H
signal not observed
“C{’H)-NMR (75 MHz, CDCI,): 6=21.3 (CCH,), 47.7 (NCHI), 64.1 (CH&
75.0 (COH), 79.1 (CHCl2)
G U M S : m / z 174 (0.05%), 172 (0.35), 170 (0.55), 149 (0.25), 102 (18), 58 (loo),
44 (lo), 42 (10); an exact determination was made of the mass from the
(M+H)’ peak of a C I (isobutane) measurement (resolving power 5000):
Mexp=186.0442; MClrlLd=
186.045245 for C a H l 4 C l 2 0 N @ .
Received: March 2, 1988 [Z 2643 IE]
German version: Angew. Chem. 100 (1988) 1005
CAS Registry numbers:
1, 2146-67-0; 2, 37555-63-8: 3, 31103-52-3; 4, 2146-66-9; 5, 114885-52-8;
6, 114885-53-9; 7, 114885-54-0; 8, 114885-55-1; 9 (R’= Ph), 2612-36-4;
9 (R’=n-CnHi3), 99706-66-8; 10 ( R 2 = P h , R’=Me), 4773-32-4; 11, 1536456-4; 12, 114838-68-5; 13, 4773-54-0; PhCH(OH)CCI,. 2000-43-3;
(CH>)sC(OH)CCI,,
3508-84-7;
IZCHTi(OiPr),Li,
114885-56-2;
CI2CHTi(OPr),Li,
1 14885-66-4;
Br2CHTi(OiPr),Li.
114885-57-3;
C12CHHf(OEt)4Li,
114885-58-4:
ClzCHHf(OEt),,
114885-59-5;
Cl2CHTi(NEt2),Li,
114885-60-8;
CI2CHTa(OEt),Li,
114885-61-9;
C12CHNb(OEt)iLi,
114885-62-0;
C12CHTi(OEt)4Li,
114885-63-I ;
(C12CH)2CuLi, 114885-64-2; C13CTi(OlPr)3, 114885-65-3: Ti(OiPr),, 546.689 ; Ti(OPr)4. 3087-37-4; Hf(OEt),, 13428-80-3; Hf(OEt),CI, 101803-59-2;
Ti(NEt&, 4419-47-0; Ta(OEt)5, 6074-84-6; Nb(OEt),, 3236-82-6; Ti(OEt),,
3087-36-3; Ti(OiPr),CI, 3712-48-9; MnC12, 7773-01-5; CuCI, 7758-89-6;
benzaldehyde, 100-52-7; heptanal, 11 1-71-7; acetophenone, 98-86-2;
3-pentanone, 96-22-0; cyclohexanone, 108-94-1.
111 T. Kauffmann, T. Abel, M. Schreer, D. Wingbermiihle, Tetrahedron 43
(1987) 2021.
121 G. Kohrich, Angew. Chem. 79 (1967) 1 5 ; Angew. Chem. Inf. Ed. Engl. 6
(1967) 41.
131 According to J. Villieras et al. (J. Villieras, R. Tarhouni, B. Kirschleger,
M. Rambaud, Bull. Sor. Chim. Fr. 1985. 825; ibid. 1986, 470) the addition
of lithium salts to Kobrich carbenoids leads to a reasonable increase in
thermal stability; consequently, better yields are achieved in additions to
carbonyl compounds.
[4] These results are mainly taken from the Dissertation by M. Wensing (Universitat Munster 1987).
15) At - I O T , the ‘H-NMR spectrum (300 MHz) of the hypothetical ate
complex 5 dissolved in [Ds]THF shows a singlet at S=5.31, which disappears at + 10°C and is therefore assigned to the proton of the C12CH
group. In the ‘,C-NMR spectrum (75 MHz; THF; [D,]benzene as internal standard) a singlet appears at 6=91.2 at -30°C; this disappears on
warming to + 1 0 T and IS therefore likewise assigned to the Cl2CH
group. A band at 495 c m - ’ in the IR spectrum (THF, - IO”C), which
disappears at + 10°C. is assigned to a Ti-C vibration, since Ti-C vibrations have already been observed in the range 427-530 c m - ’ for Ti-methy1 complexes (G. L. Karapinka, J . J. Smith, W. L. Carrick, J . Polym. Sri.
SO(1961) 143; G. W. A. Fowles, D. A. Rice, J. D. Wilkins, J . Chem. Sor.
A 1971. 1920).
[6] U p to 85-95% of the unchanged carbonyl compounds was recovered.
171 “Grouping” = combination of functional groups; see T. Kauffmann, T.
Moiler, H. Rennefeld, S. Welke, R. Wieschollek, Angew. Chem. 97 (1985)
351; Angew. Chem. In(. Ed Engl. 24 (1985) 348.
944
0 VCH VerlagsgesellsehaJi mbH, 0-6940 Weinheim, 1988
Me2
MeC13TidN)
YN
Me,L
Za
[MeTiCI3(PPh3)]
2b
[MeTiCL3( PPh3)2]
2c
Scheme 1. 141.
pounds. In these investigations it was found[31that, in reactions with aldehyde/ketone pairs, the triphenylphosphane
complexes 2b and 2c preferably methylate the ketone, that
is in complete contrast to the tmeda-complex 2a, which
methylates aldehydes in CHzClzand is almost inert toward
ketones (Table 1).
Table 1. Reactions of phosphane complexes of the compound 1 as pure substances with substrate pairs in CHCll at -25°C (6 h).
Substrates
A/ B
HeptanaV
2-hexanone
Ligand
Molar ratio
Ligand : 1 : A : B
Methylation
product [%I
ofA ofB
Recovery
[%I
A
B
97
30
-
0:I: I :I
74
PPh,
PPh,
doue
dppe
2:2:1:1
4 : 2 : 1 : 1 [a]
2:2:l:I
2:2:I:l[a]
0.1 : I : I
2 :2 : 1 : I [a]
10
9
4
27
60
4
95
19
89
22
88
87
90
73
30
84
0:I.I:l
2:2:1:1 [a]
89
3
6
69
9
94
90
26
0:1 : I : I
2 :I :1 :I
45
3
I
3
17
30
62
74
95
61
53
94
98
94
81
69
34
25
4
39
Heptanall
cyclohexanone
Cyclohexanecarbaldehydel
2-hexanone
-
Cyclohexanecarbaldehydel
cyclohexanone
PPh,
PPh,
PPh,
dppe
PPh,
-
PPh,
-
4 :2 : I : 1
4 :2 : I : 1 [a]
l:l:l:l
3
67
81
51
5
44
2
70
0
[a] Reaction at 0°C instead of at -25°C (6 h)
An analogous ketone selectivity was found, albeit somewhat less pronounced, in the case of the complex formed
from P.P‘-ethylenebis(dipheny1phosphane) (dppe) and 1
(Table 1).
The ketone selectivity of the complex 2b can be attributed (and the same holds true for 242) to the fact that a
[*I
Prof. Dr. T. Kauffmann, DiplLChem. T. Abel, Dip1.-Chem. M. Schreer
Organisch-chemisches lnstitut der Universitgt
Corrensstrasse 40, 0-4400 Miinster (FRG)
[**I Transition Metal-Activated Organic Compounds, Part 27. This work was
supported by the Deutsche Forschungsgemeinschaft, the Stiftung Volkswagenwerk, and the Fonds der Chemischen 1ndustrie.-Part 26: [I].
0570-0833/88/0707-0944 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 27 (1988) No. 7
tains a five-membered ring, whereas the complex 5 analogous to 3a contains a seven-membered ring.
YPh3
2b
+
O=CH-R
+[MeCL3Ti+O=CH-R]
0
PPh,
+
0
MeCL3Ti-O-AH-R
o/
/
MeCL2Ti-O-CH-R
3a
Mec,3Tidp)
YD
3b
2d
Scheme 2. R
=
\
Ph2P
I
Ph2
n-C6H13-CH0,
LPh2
n-C,H,,-CH
TiC13Me
\ -10
U
Ph2
5
n-hexyl.
phosphoniumalkoxy complex of type 3a o r 3b is formed
in reactions with aldehydes according to Scheme 2,
whereby the aldehyde function is blocked. In the case of
ketones, on the other hand, it is not the phosphane ligand
but the methyl group that is transferred. Since 2-hexanone
is still methylated to the extent of 28% in the reaction of 2b
with heptanaW2-hexanone in the molar ratio 1 : 1 : 1 (instead of 2 : 1 :1) it can be assumed that not only 2b but also
the phosphoniumalkoxy complexes 3a or 3b formed
therefrom are effective methylating agents.
The assumption of phosphoniumalkoxy compounds
such as 3a or 3b as intermediates is supported by the following findings:
a) In the IR spectrum of the complex prepared from 2b
and heptanal in CH,CI, the carbonyl band expected to appear at ca. 1720 cm-’ is absent, but several strong bands
are observed at ca. 1120 cm-’ that can be assigned t o C-0
vibrations, since transition metal alkoxides strongly absorb
in the 1000-1200 c m - ’ region.
b) The ”P-NMR signal of the complex formed from 2b
and heptanal in CDCl3 is shifted markedly downfield
(6=20.0) compared to that of PPh3 (6= -6.0) and 2b
(S= 10.0), clearly indicating a triphenylphosphonium
group (for comparison: 4b: 6 = 17.6).
Complexes analogous to 3af3b have also been detected
spectroscopically in reactions of [MeNbClr(PPh3)] 6,
[TiCl4(PPh3)] 7, and [NbCl,(PPh,)] with aldehydes. The
niobium complex 6 blocks the aldehyde group of heptanal, but (in contrast to 2b) not that of benzaldehyde. This
enabled the selective methylation of benzaldehyde according to Scheme 3. The complexes analogous to 6 with NPh3
or AsPh, instead of PPh3 did not block the aldehyde group
of heptanal.
n-CsHI 1 -CH(OH)CH3
+ Ph-CH(CI)CH,
79%
7%
Scheme 3. [7].
Methylation according to Scheme 4 could be achieved
with the complex 7.The scope of application of this particularly convenient ketoselective alkylation method is presently under investigation.
heptanal
+ 2-hexanone
127;t:$:2
)
2-octanol
14%
+ 2-methyl-2-hexanol
59%
Scheme 4 [31.Reaction temperature 0 ° C ( 6 h)
4a, R = ALkyl
b. R = OMe
C , R = CL
I
OCH2R
c) In the I3C-NMR spectrum of the complex formed
from 2b and heptanal in CDCI, the 6 values for the phenyl
C-atoms are very similar to those for the phosphonium salt
4.15]The same holds true for the coupling constants ’ J , i p ~ , c
(Table 2).
Reetz et al.[’] reported comparable possibilities of the reversal of selectivity by in-situ blocking of aldehyde groups:
The reagent [(allyl)Ti(NMe2)4MgC1]can be used for the selective allylation of a keto function in presence of an aldehyde function (one step method), whereas in the corresponding alkylations the aldehyde function must be chemoselectively blocked by addition of [Ti(NEt,),] and the keto
function must be alkylated with moderately nucleophilic
reagents (two-step method). The reversal of selectivity by
use of phosphane complexes described here could be preparatively attractive because of the very easy access of the
reagents.
Table 2. 6(”C) and coupling constants ’J(”P,’3C) [Hz](in brackets) of the
complex 3 formed from 2b and heptanal in CDCI, (20°C)and of the compounds 4 [5]Compound
“C
Complex 3a/3b
4a
4b
4c
116.9
(80.0)
i17-ii9
(80-89)
117.0
(85.9)
116.5
(88.3)
Indexing according t o 3b and 4
bC
‘C
dC
134.0
(9.0)
134
(9-11)
136.6
(10.0)
134.6
(10.2)
130.0
(12.0)
131
(12-13)
131.1
(12.8)
130.9
(13.0)
135.0
135
(3)
135.9
(3.1)
136.0
(3.0)
‘C
85
(56)
11-35
66.2
(69.4)
33.8
(56.8)
Table 1 shows that on using 1 f d p p e (the known complex 2dI6]may be formed thereby) aldehyde groups are less
effectively blocked. This is understandable since 2d conAngew. Chem. Int. Ed. Engl. 27/1988) No. 7
Received: March 7, 1988 [Z 2650 IE]
German version: Angew. Chem. 100 (1988) 1006
[I] T. Kauffmann, R. Fobker, M. Wensing, Angew. Chem. I00 (1988) 1005;
Angew. Chem. Int. Ed. Engl. 27 (1988)943.
[2] T. Kauffmann, T. Abel, M. Schreer, D. Wingbermuhle, Tetrahedron 43
(1987)2021, footnote [7b].
131 T.Abel, T. Kauffmann, unpublished.
141 The decreasing nucleophilicity of 1 in the given sequence is due to the
increasing blocking of coordination sites without heterolysis of the TiCH, bond taking place.
[5] C.A. Gray, J. Am. Chem. SOC.95 (1973)7736.
[6]G. W. A. Fowles, D. A. Rice, J. P. Wilkins, J . Chem. Soc. A 1971. 1920.
[7] As observed in the reaction of Me2NbCI, with benzaldehyde (J. D. Wilkins, J. Organomet. Chem. 80 (1974)357), the reaction of 6 with benzaldehyde causes, besides methylation, the exchange of the oxygen function
for chlorine. This chlorination process occurs via radicals: M. Schreer. T.
Kauffmann, unpublished.
181 M. T. Reetz, B. Wenderoth, Tetrahedron L e f f . 23 (1982) 5259; M. T.
Reetz, B. Wenderoth, R. Peter, J . Chem. SOC.Chem. Commun. 1983. 406;
M.T.Reetz, Top. Curr. Chem. 106 (1982) I.
0 VCH Verlagsgesellschafl mbH. 0-6940 Weinheim. 1988
0570-0833/88/0707-0945 S 02.5010
945
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aldehyde, titanium, formation, niobium, triphenylphosphoniumalkoxy, complexes, function, blocking, situ
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