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Isolation and Decomposition of the Intermediate of an ElcB Elimination.

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evidence based on ORD and CD data for (-1) and a variety
of sulfoxides, including ( + 3 ) , which is in complete accord with
our present finding of an ( R ) configuration for ( + 3 ) .
Thus, the evidence is now complete for rigorous formulation
of the Grignard synthesis of optically active sulfoxides as
proceeding with inversion of configuration at asymmetric
sulfur.
(-2),
x=1
(+3)
On the basis of ORD and CD evidence for (+)-phenyl p-tolyl
sulfoxide ( + 4 ) , Mislow e t at. [2J have assigned the ( R ) configuration to this substance as derived from (-1) by an inversion path in the Grignard synthesis. We have extended
this synthesis of (+4) to include organometallic reagents
other than the Grignard (Table 1). It is of considerable
interest that rather drastic changes in the nature of the
organometallic reagent leave both the stereochemical path
and the stereospecificity unchanged. In the case of methylmethoxy-a-naphthylphenylsilane,sensitivity of stereochemistry to the nature of the organometallic reagent has been
demonstrated for nucleophilic displacement of methoxy.
Table 1. Phenyl p-tolyl sulfoxide from (-)-menthy1 (-)-(S)-p-toluenesulfinate (-1) Ial.
CaHsMgBr
(CaHsfzZn [C]
(CsHs)zCd[cI
1
(R)- (+)
(R)- (+)
(R)
-
(+)
1 1:;:; 1 1
+21.2
90-92
90-92
90-92
[4] International Tables for X-ray Crystallography. Vol. 111,
Kynoch Press, 1962.
[5] W. H . Zachariusen, Acta crystallogr. 16, 1139 (1963).
[6] W. C . Hamilton, Acta Crystallogr. I S , 502 (1965).
[7] It appears that in many cases absolute configurations can be
determined by X-ray methods both more rigorously and at lower
cost than by the use of the more usual methods of organic chemistry.
[S] L. H . Sommer and W.D . Korte, J. Amer. chem. SOC.89, 5802
(1967). Some of the data reported in this reference furnished
motivation for our present rigorous demonstration of inversion
for reaction (1)+(3).
[9] L . H. Summer: Stereochemistry, Mechanism and Silicon.
McGraw-Hill, New York 1965.
[lo] See, for example, C. R . Johnson and D. McCants, Jr., J.
Amer. chem. SOC.87, 5404 (1965) and earlier references cited
therein; A . Nudelman and D. J. Cram, J. Amer. chem. SOC.90,
3869 (1968).
Isolation and Decomposition of the Intermediate
of an ElcB Elimination
By A . Berndt [*I
ElcB reactions are two-step 1,2-eliminations; in the first step
the conjugate base (2) is formed from the substrate (1); in
the second step (2) decomposes by wayiof a first order reaction to give the elimination product (3) and X e [I].
73
70
68
[a] [ a l =
~- -198 O (in acetone).
[b] C6HSLi metalates the benzylic protons in ( - 1 ) .
[c] The reactions were r u n in refluxing benzene for 16 hours.
Simple aikyl or aryl organometallic reagents (Grignards and
RLi reagents) give retention of configuration, whereas chargedelocalized reagents such as C6HSCHzLi give inversion of
configuration 181. In the organosilicon stereochemistry of
monofunctional R$i*-systems, inversion and an s ~ 2 - S
mechanism appear to be the most common, but many examples of retention reactions involving poor leaving groups
are also known [91. In organosulfur stereochemistry, nucleophilic displacement reactions at the asymmetric sulfur center
appear, thus far, to involve only inversion of configuration [1OJ.
Received: May 27, 1967
[Z 39 IEI
German version: Angew. Chem. 81, 619 (1969)
[*I Prof. H. Hope, Dr. U. de la Camp, G. D. Homer [**I,
A. W. Messing, and Prof. L. H. Sommer
Department of Chemistry
University of California
Davis, California 95616 (USA)
[**I National Institutes of Health Predoctoral Fellow.
[***I We thank the National Science Foundation for support
of this work.
[l] K . K . Andersen, Tetrahedron Letters 1962, 93.
I21 K . Mislow, M . M . Green, P . Lauer, J . T. Melillo, T. Simmons,
and A . L . Ternay, Jr., J. Amer. chem. SOC.87, 1958 (1965).
[3] E. B. Fleisher, M . Axelrod, M . Green, and K . Mislow, J. Amer.
chem. SOC.86, 3394 (1964).
In all previous investigations, (2) occurred in such low concentration that its intermediary character could be detected
only indirectly 121. We have now been able to isolate the conjugate base of a 1,2-elimination in substance and investigate
the kinetics of its decomposition in solution.
If a solution of ( l a ) 131 in ether is added with stirring to an
ice-cooled saturated solution of NH3 in ether, a yellowishwhite precipitate separates after I-10 minutes which is
also insoluble in other aprotic organic solvents and in water.
The substance can be recrystallized from methanol at temperatures below 0 "C. It melts at 85-90 'C. C, H, N analyses
and the other experimental data support the structure of the
ammonium salt of the conjugate base (Za) (ammonium
3-tert-butyl-4,4-dimethyl-2,3-dinitro-2-pentanide),which is
obtained in almost quantitative yield. In methanol, the NH4
salt of (2a) decomposes within a few minutes at 30 "C to give
nitrite and the olefin (3a). which cyclizes to 4,4-di-tert-butyl3-methyl-4H-1.2-oxazete N-oxide ( 4 ) [41. In the solid state the
NH4 salt of (2a) is transformed into ( 4 ) within a few weeks.
On shaking a suspension of the salt in chloroform with dilute
mineral acid, products are obtained in which only the nitro
group at C-3 is still present in the molecule[~l;this nitro
group cleaves off as nitrite during the elimination. It is thus
shown that (20) still contains both nitro groups.
H3C\
C - C R ~+ NH,
OZN'I:
ko,
+
N H ~
R = C(CH,),
Angew. Chem. internat. Edit. 1 Vol. 8 (1969)1 No. 8
613
This finding is confirmed by the I R spectrum of the salt of
(2u) (in Nujol) which shows, beside the band of the NH4@
ion, two bands at 1510 and 155Ocm-1 in the region of the
assymetric vibrations of nitro groups. The NMR spectrum
(in C D 3 0 D at 10°C) shows two singlets at 6 = 2.18 and
1.37 ppm in the ratio 1:6.
The kinetics of decomposition of (2u) was studied by NMR
spectroscopy (in C D 3 0 D between 20 and 33 "C). In all the
cases investigated the results pointed to reactions of first
order, the half-lives being between cu. 10 minutes at 20°C
and ca. 2 minutes at 30 "C. The activation energy of the decomposition proved to be 22 5 kcal/moIe.
*
The unusual stability of the ammonium salt of (2u) must be
due to steric hindrance; no intermediate can be isolated in
the case of 2-tert-butyl-3,3-dimethyl-l.2-dinitrobutane,which
contains only one methyl group less than (la).
Received: May 19, 1969
[Z 7 IE]
German version: Angew. Chem. 81, 567 (1969)
[*I Dr. A. Berndt
Institut fur Organische Chemie der Universitat
355 Marhurg, Bahnhofstrasse 7 (Germany)
[I] C. K . ZngoId Structure and Mechanism in Organic Chemstry. Cornell University Press, New York 1953, p. 423.
[2] D. J. McLennan, Quart. Rev. 21, 490 (1967).
[3] A . Berndt, Tetrahedron 25, 37 (1969).
[4] A . Berndt, Angew. Chem. 80, 666 (1968); Angew. Chem.
internat. Edit. 7, 637 (1968).
IS] A. Berndt, unpublished results.
H
'P=N'
H
/I
/I
H
(1)
(4)
(3)
(2)
Previously, the sole exception to this rule were compounds in
which the phosphazene grouping (2) is part of a cyclotriphosphazene ring (3) or triazaphosphorine ring (4) [61.
Is the (P)H form possible only as a part of such a ring system
or may it not be achieved even in simple, open-chain compounds by suitable substituent effects?Substituents X capable
of increasing the basicity at the P atom and substituents Y
capable of increasing the acidity at the N atom should favor
the bonding of the proton to the phosphorus i.e. favor structure (21; on the other hand, however, they should also weaken
the phosphazene bond and the stability of (2).
A compound in which X = NR2 and Y = SOzR would represent a typical case in this connection. Such a compound
can be prepared from the aminochlorophosphine (51, X =
N(CH3)2, and the sodium salt of p-toluenesulfonamide (6).
Adverse
~.
secondary reactions can be
Y = SOZC~H~CH
avoided by keeping the concentration of (5) very low. The
product is a colorless, viscous liquid that does not react with
sulfur in boiling benzene as would be expected for an aminophosphine (I). The 1R spectrum shows the characteristic absorptions of the P-H- and P=N-vibrations (Table) and thus
substantiates the phosphazene structure (2). The most convincing evidence for structure (7). however, is provided by
the large doublet splitting of the NMR signals of the single
proton and of the phosphorus.
The Prototropic System Aminophosphine/
Iminophosphoranerll
X
I
(CH&N-P-CI
X
+ NH-YQ
I
+ (CH&N--P=NY
I
H
By A. Schmidpeter and H . Rossknecht [*I
(5)
Although hydroxyphosphines as such are, with very few exceptions, unstable and rearrange to phosphine oxides with
transference of the proton onto the phosphorus, quite the
reverse is the rule in the case of aminophosphines (phosphazanes) (I). Phosphazanes are always present as such and no
proton migration from nitrogen to phosphorus takes place not even in the sense of an equilibrium[21: Accordingly (P)Himinophosphoranes (phosphazenes) also could not be
prepared; they rearrange spontaneously to the tautomeric
(N)H-aminophosphines ( I ) [3*4,51.
(6)
( 7)
A similar result is obtained in the reaction of ( 5 ) with the
potassium salt of diphenylthiophosphoric, diphenylphosphinic, or diphenylthiophosphinic acid amide ( 6 ) , Y =
PS(OC6H5)2, PO(C6H&, PS(CsH5)2, if it is carried out at
-70 "C, thus avoiding side-reactions. The (P)H-iminophosphorane (7) is formed in each case. The values vPH and JPH
for the compounds ( 7 k d ) obtained from the above mentioned series of amides change proportionally (71 and decrease
both with decreasing acidity of the amide.
17cl
(7el
SOZC~H~CH~
CH3
Y
X
~~
IR Bands (cm-1)
vP-H
vP=N
2450 w, 2370 w
1200 vs
2410 m, 2350 sh
1220 vs
2400 sh. 2340 w
119ovs
2400 m, 2350 sh
1140 vs
-21.5;
double tredecalet
-23.3;
doublet [bl
-52.7; doublet
-6.90 [cl;
double doublet
-2.48: doublet
-22.4;
doublet [bl
-12.0 [bI
-6.86;
double doublet
-2.48: doublet
-24.4;
doublet [bl
-42.5 [bl
-7.12;
double doublet
-2.50: doublet
+1.4;
doublet tb]
583
51
3.5
575
[dl
3.2
564
[dl
4.0
508
11.7
12.2
11.7
-2.52: doublet
Spin-spin coupling (Hz)
JPH
JPNP
JPNPH
JPCH
JPNCH
~
~
2460 m. 2400 sh
1140 vs
-6.82; doublet
[a1
[bl
[cl
Id]
[el
+ Cle
587
11.6
-7.07;
doublet [cl
-2.53; doublet
-1.66; doublet
14.0
12.4
Measured in CHzClz against 8 5 % phosphoric acid (external) or TMS (internal); shifts to lower field strengths negative.
Signal or signal components broadened by splitting, multiplet structure not (clearly) recognizable.
Indirect, not measurable directly because of superposition.
Not measurable because of superposition.
We are grateful to Dip1.-Chem. K. Schumunn for recording the SIP-NMR spectra.
614
Angew. Chem. internat. Edit. f Vol. 8 (1969) 1No. 8
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