1. Art and Diseño

Tetrahedron Letters No. 29, pp 2495 - 2496, 1977.
Pergamon Press. printed in Great Britain.
THE CARBONn INSERTION REACTIONS OF MIXED
TERVALENT PHOSPHORUS-ORGANOSILICONREAGENTS
D. A. Evans,* K. M. Hurst, L. K. Truesdale and J. M. Takacs
Contribution No. 5593 from the Laboratorfes of Chemistry
California Institute of Technology, Pasadena, California 91125
(Received in USA 1 Nay 1977; received in UI( for publication 8 June 1977)
In conjunction with our general interest in the development of synthetic operations which
1
reverse the normal polar reactivity patterns of the carbonyl function, we have been focusing
our attention on carbonyl derivatives which could serve as operational equivalents to the hypothetical carbanions 1 and 2.2,3 In this regard we have been engaged in the development of
organosilicon reagents 2 containing potential carbanion-stabilizingfunctions, A, which will
In principle, such carbonyl derivatives, upon
undergo facile carbonyl addition (eq. 1).
metalation, should serve as valuable carbon nucleophi.lesin organic synthesis. During the
course of this study, a series of brief notes appeared on the reaction of tervalent phosphorus
reagents &
and G
with saturated aldehydes and ketones (eq. 2) to give phosphonates k4
phosphonamidesz5
respectively (Method A).
and
A complementary method for converting aliphatic
and aromatic aldehydes into Wsiloxyphosphonates (eq. 3) has been described in tl..:
patent
literature (Method B),6
8
R-C:-
R
-:CH2CH2C-R
Rl\C=O
/
R2
8
R-C-H
OSiR’3
+ R’3SiA
--c
R-#-A
(1)
~SiMe3
+
Me3SiOPX2
&
Rl-y-p2
%
2, X = 0-Alkyl
Method A
(2)
Method B
(3)
RZO
k, X = NEt2
RI\C=O
QSiR3
+ PX3 + R3SiCl
&
R1-F-f;X2
H 0
H/
2495
No.
2496
29
The purpose of this connnunicationis to report our observations on the scope of these
carbonyl addition processes with a,B-unsaturated ketones and aldehydes. Of particular interest
in this study has been the regiochemistry (1,2 vs 1,4-addition) and probable mechanism of these
addition processes, a point which has not been dealt with in previous studies (Scheme I).
pSI$
RlCH=CH-_F-$X2
x
Rz O
R
RICH=CHC-R2
+
ymg
X2fj-r-CH=C-R2
Method
B
5
1
Three silicon-phosphorusreagents 5 were prepared for study. Dimethyl trimethylsilyl phosphite [TMSOP(OMe),land dimethyl triethylsilyl phosphite [TESOP(OMe)2]were
4b
prepared by known procedures.
Triethylsilyl N,N,N',N'-tetramethylphosphorodiamidite
[TFSOP(NMe2)21was prepared from N,N,N',N'-tetramethylphosphorodiamido
chloride7 and
triethylsilanol in ether/triethylamine(bp 66-74"c, 0.02 mm;
55% yield).* The reactions
of the mixed silicon-phosphorusreagents 2 (Method A) with a series of CT,&unsaturated
aldehydes and ketones were carried out with one equivalent of each reagent either neat or in
THF under an inert atmosphere. The aldehyde addition reactions generally proceeded at a convenient rate at ambient temperatureswhile ketonic substrates required heating. The complementary addition reac'ions employing the phosphite esters, PX.,,and chlorosilanes (Method B),
6
as described by Birnum, were carried out with stoichiometric quantities of each reagent, neat,
at the indicated temperatures in sealed ampules (Table). Qualitatively, the relative reactivities
of the tervalent phosphorus reagent, PX3, followed the general order: ROP(NMe2)2 >> ROPPh2 >
(R0)3P (c.f. Entries 10-12). This trend is consistent with the relative nucleophilicities of
9
related phosphorus derivatives towards alkyl halides. The possibility that the 1,2 and 1,4adducts L and 8 might be interconverted thermally was eliminated by the following experiment:
The crotonaldehyde 1,2 and 1,4-adducts (Entry 5, Table) were individually heated (200°c, 24 h),
and no interconversionwas detected. The high thermal stability observed in this instance
suggests that the 1,2:1,4-adductratios reported in the Table are a consequence of kinetic
control during the addition process. From a mechanistic standpoint the two methods reported
herein differ in that Method A involves intramolecular silicon transfer during t..eaddition
pr0cess.l' Furthermore, we have determined that under the conditions employed for Method B,
the mixed silicon phosphorus reagent 5 is not an intermediate. One rational mechanism for the
1,2-addition of the tervalent phosphorus-siliconreagent 5 to carbonyl substrates is illustrated
in Scheme 11.10 In those cases where 1,4-addition is possible, several observations suggest
that addition proceeds e
the oxaphospholenesg (Method A) and 2 (Method B). First, the
2497
No. 29
a.
Addttion Reactions of Mixed Phosphorus Reagents to Carbonyl Substrates (Scheme I).8
Entry
Substrate
PX3 (Method)
Conditionsa
7.Yiel&
Ratio (z:g)
1,2:1,4_addition
47~53
1
CH2 = CHCHO
TMSOP(OMe), (A)
25", 12 h
aa
2
CH2=CHCH0
(MeO)3P/TMSCl (B)
2S", 4 h
JO
> 99:l
3
CH2=CHCH0
TESOP(NMe2)2 (A)
00, l/4 &
90
> 99:l
4
CH2=CHCH0
Ph2PoMe/T&
loo", l/2 h
5
CH3CH=CHCH0
TMSOP(OMe)2 (A)
550, 18 h
90
6
CH3CH=CHCH0
(MeO)3P/TkfSCl
(B)
55", 3 h
62
> 99:l
7
CH3CH=CHCIIO
TESOP(NMe2)2 (A)
00, l/2 fi
95
> 99:l
8
PhCH=CHCHO
TESOP(NMe2)2 (A)
O", l/2 $
93
> 99:l
9
CH =CH!CH
2
3
SO", 6 h
88
<
1:YY
10
P
CH2=CHCCH3
100°, 2 h
79
<
1:YY
11
P
CH2=CHCCH3
0", l/2 hg
82
c
1:YY
12
P
CH2=CHCCH3
(100)
<
1:YY
(B)
(MeO)3P/TBSCl (B)
Ph2POCH3/TESClg (B)
loo", l/2 h
<
(100)
1:YY
JS:25
sxcept where noted the reactions were carried out in the absence of solvent. ILyieldsreported
are of distilled adducts. Yields in parenthesis were determined by nmr. In suchdcases distillation resulted in decomposition. qhe reaction was carried out 3 M in THF. -Available
from Aldrich Chemical Company.
olefin geometry of the 1,4-adducts$, R = H, Me (Entries 4, 9, 10, 12, Table), is exclusively
i?,a possible consequence of the intervention of oxaphospholenes such as g
and 2.
Second,
CT,B-unsaturated
ketones locked in a transoid geometry such as cyclohexenone fail to undergo
9
detectable 1,4-addition. Finally, we have prepared the known oxaphospholene g
(R = Me)
11
and have demonstrated that it undergoes a rapid exothermic reaction with trimethylchlorosilane
to give the Z-phosphonate 8 (R = Me, X = OMe) in nuantitative yield.
In conclusion, through a judicious choice of the phosphorus reagent one may achieve high
regioselectivity for either 1,2 or 1,4-addition to a#-unsaturated aldehydes, and regiospecific
l&-addition to methyl vinyl ketone and presumably to related enones. The general class of
phosphorus-activatedCLefins 2 and 2 (Scheme I) should prove to be useful carbon nuoleophiles
upon metalation. These studies are now in progress.
2498
No.
29
Scheme II
Rl\,C=O
+ X2POSiMe3
1-
__c
.&Nm
R1 R2 II 2
0
X2+
4
8
CH2=CHCR
S)SiMe3
I\_
8,
OSiMe3
We013P
B.
Research support from the National Science Foundation is gratefully acknowl-
edged. We wish to thank J. Kouba for technical assistance in this project.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
D.A. Evans and G.C. Andrews, Accounts Chem. Res., z, 147 (1974).
For an excellent survey of acyl anionequivalents see O.W. Lever, Jr., Tetrahedron, 32,
1943 (1976).
D.A. Evans, G.C. Andrews and B. Buckwalter, J. Am. Chem. Sot., 9-6,5560 (1974).
(a) For a leading reference, see I.V. Konovalova, L.A. Burnaeva, N. Sh. Saifullina and
A.N. Pudovik, J. Gen. Chem., USSR, 5, 17 (1976); (b) L.V. Nesterov et al., ibid.
41 2655 (1971).
2474 (1971); Z.S. Novikova, ibid., _,
A.N. Pudovik, E.S. Batyeva and V.A. Al'fonsov, J. Gen. Chem., USSR, g, 921 (1975); A.N.
Pudovik, E.S. Batyeva and V.A. Al'fonsov, ibid., 240 (1975).
G.H. Birum and G.A. Richardson, U.S. Patent 3, 113: 139 (1963).
H. Noth and H.-J. Vetter, Chem. Ber., 2, 1505 (1961).
Satisfactory s:ectral and combustion analyses were obtained for all new compounds.
R.G. Pearson, H. Sobel and J. Songstad, J. Am. Chem. Sot., 9&)-319 (1968); G. Aksnes and
D. Aksnes, Acta Chem. Stand., l8, 38 (1964).
Appropriate cross-over experiments testing this point will be detailed in a later publication.
D. Gorenstein and F.W. Westheimer, J. Am. Chem. Sot., 92, 634 (1970).