REACTION OF TRISDIALKYLAMINOPHOSPHINES WITH AROMATIC ALDEHYDES 13
Vol. $8, No. 1, January 1968
Reaction of Trisdialkylaminophosphines with Aromatic Aldehydes. I. The Nitrobenzaldehydes. Formation of 2,2,2-Trisamino-1,3,2-dioxaphospholanes and Their Conversion into Epoxides FAUSTO RAMIREZ,~ A. S. GULATI,AND C. P. SMITH Chemistry Department, State University of New York at S h y Brook, Stony Brook, New York 11700 Received July 14, 1967 The phosphorus of trisdialkylaminophosphines attacked the carbonyl oxygen of 0-, m-,and p-nitrobenzaldehydes. The resulting 1 :1 adducts with Pa-C bonds added to a second molecule of the aldehyde and formed 2:1adducts. The 2:1 adducts were isolated as stable 2,2,2-triamino-1,3,2dioxaphospholanesin the case of fivemembered cyclic trisdialkylaminophosphines. These phosphoranes were converted at 80" into dinitrostilbene oxides and the amidates with inversion of configuration at carbon. The 2:1 adducts derived from open-chain trisdialkylaminophosphjnee were unstable even below 0" and gave the dinitrostilbene oxides. The Pal nmr shifts are described.
Previous papers from this laboratory have dealt with the mechanism of the reactions of trialkyl phosphites and of trisdialk~laminophosphineswith a variety of In all cases the phosphorus of the trivalent phosphorus compound added to the oxygen of the carbonyl function to form 1:1 adducts with P-0-C bonds, provided that, the carbonyl function was activated by electron-withdrawing substituents. The types of structures that have been obtained and corresponding values of P31nmr shifts are shown in 11-VI.
$w n
Rw-C
X R,
= =
-t PX,
0 OR, NRs
-
fiw
+
Rw-+,PX3
0 I
electron-withdrawing groups
R
R
I
c=c
A
I I
CH30b&H3
I
OCH,
11.6Pal = +44
R
I
C C -
R
I
I
111. 6P31
CF3
R
R
I
R
I
I
R
c=c
1
U V, 6Pal = -39 ppm to -35 PPm
VI, 6Pa1 = +35 ppm to +42 ppm
The reaction of hexafluoroacetone with a five-membered cyclic aminophosphine gave the stable 2,2,2-triamino-1,3,2-dioxaphospholane (VII). However, the reaction with an acyclic aminophosphine led to very unstable 1: 1 and 2: 1 adducts, VI11 and IX, respectively, which underwent molecular fragmentations to several products at about 0".
CF3
I
I
CF3-C-C-CF, 0. / CH30-P-OCH,
CF3+
' 6 I
I
OCH,
=
IV. 6P31 =
(1) This work was supported by National Science Foundation Grant, GP-3341 and by the Public Health Service Grant CA-04789-06-08 from the National Cancer Institute. (2) F. Ramirez. C. P. Smith, A. S. Gulati. and A. V. Patwardhan, Tetrahedron Letters, 2151 (1966). (3) F. Ramirez, C. P. Smith, and S. Meyerson, ibid., 3651 (1966). (4) F. Ramires, A. S. Gulati, and C. P. Smith, J . A m . Chem. SOC.,89,6283 (1967). (5) For other work on the reaction6 of hexafluoroacetone with trialkyl phosphites, see (a) N. P. Gambaryan, Yu. A. Cheburkov, and I. L. Knunyants, BUZZ. Acad. Sci., USSR, 8 , 1433 (1964); (b) E. M. Rokhlin, Yu. V. Zeifman, Yu. A. Cheburkov, N. P. Gambaryan, a n d I . L. Knunyants, Dokl. Akad. Nauk SSSR. 161, 1356 (1965). (6) (a) F. Ramirea and C. P. Smith, Chem. Commun., 662 (1967); (b) I. J. Borowitz and M. Anschel, Tetrahedron Letters, 1517 (1967). (7) (a) F. Ramirea and N. B. Desai, J . A m . Chem. SOC.,8% 2652 (1960); (h) ibid., 86, 3252 (1963). ( 8 ) (a) F. Ramirez, A. V. Patwardhan, H. J. Kugler, and C. P. Smith, Telrahedmn Letters, 3053 (1966); (b) F. Ramirea, A. V. Patwardhan, H. J. Kugler, and C. P. Smith, Tetrahedron, in press. (9) For other work on the reactions of trialkyl phosphites with a-diketones, see (8) G. H. Birum and J. L. Dever, Abstracts, 135th National Meeting of the American Chemical Society, Chicago, Ill., Sept 1958, p 101P. (10) K. M. Kirillova and V. A. Kuhktin, Zh. Obsheh. Khim., 86, 544 (1965); Chem. Abstr., a,5236 (1965). (11) (a) F. Ramires, A. V. Patwardhan, and C. P. Smith, J . A m . Chem. Soc., 87, 4973 (1965); (b) F. Ramirea, A. V. Patwardhan, H. J. Kugler, and C. P. Smith, ibid., 89, 6276 (1967). (12) (a) F. Ramirea. A. V. I'atwardhan, and C. P. Smith, J . 010. Chem. SO, 2575 (1965); (b) F. Ramirez, S. B. Bhatia, and C. P. Smith, ibid., 81, 4105 (1966).
VII, 6P3l
=
+31 ppm
VI11
IX
The behavior of aldehydes toward trialkyl phosphites has also been studied.l6J6 Again, the phosphite added to the carbonyl oxygen of aromatic aldehydes that had electron-withdrawing substituents. The products were 2,2,2-trialkoxy-1,3,2-dioxophospholanes, x-XII.
yw 2H-C
II 0
+
yw P(OCH3)S
---t
yw
H-C-C-H
I
o,p/o CH30'
I
IO' CH,
OCH,
'bpii
= ca.
+50ppm
The unsubstituted aliphatic monoaldehydes behaved differently toward trialkyl phosphites. Now, the phosphorus of the phosphites attacked the carbonyl (13) F. Ramirez, N. B. Desai. and N. Ramanathan, Tetrahedron Letters, 323 (1963). (14) F. Ramirez, M. Nagabhushanam, and C. P. Smith, Tetrahedron, in prees. (15) F. Ramirez, 9. B. Bhatia, and C. P. Smith, ibid., PI), 2067 (1967). (16) F. Ramirez, 9. B. Bhatia, A. V. Patwardhan, and C. P. Smith, J . O w . Chsm., 8% 2194 (1967).
The Journal of Organic Chemistry
14 RAMIREZ, GULATI,AND SMITH carbon of the aldehydes,l7 forming 2,2,2-trialkoxy-1,4,2dioxaphospholanes, XIII. It is entirely possible that the reactions of phosphites with aldehydes involved in all cases two sets of equilibria, one between the reactants and the 1: t adducts with P-C-0 bonds, and the other between the reactants and the 1:1 adducts with P-0-C bonds. However, the P-0-C adducts would be sufficiently stable only in those cases in which the negative charge on carbonyl carbon is stabilized by electron-withdrawing groups. It is also possible that the two types of 1:1 adducts may be interconvertible through an intermediate or a transition state having a three-membered ring and pentavalent phosphorus. These questions have not been resolved.
aldehyde to form 2: 1 dipolar adducts, XV. The latter were said to be in equilibrium with the cyclic 2,2,2triamino-1,4,2-dioxaphospholanes, XVI, which reopened with the rupture of a P-C bond to the dipolar structure, XVII. This new intermediate, XVII, then gave the epoxides, XVIII, and the amidates, XIX (Scheme I). SCHEME I
-1
+
P[N(CH3)J3
0
-
R I H-C
R
I
I
0-
P
I
0-
__
R I II-C II
0
+
P(OR),
R I f H-Y-,P(OR),
0 '
F The theoretical aspects of the reactions of trivalent phosphorus compounds with carbonyl compounds have received considerable attention in the last few years.l8 To provide more information on these questions, we have now examined the behavior of aldehydes with a series of acyclic and of five-membered cyclic trisdialkylaminophosphines. The results are reported in this and in subsequent papers. ;\Inrk19v20concluded recently that the reactions of t'risdimethylaminophosphine with aliphatic aldehydes and with aromatic aldehydes, having electron-withdrawing and electron-releasing substituents, gave in all cases 1 : l adducts with P-C-0 bonds, XIV. He reported the P31 nmr shifts, 6P31 = -32 to -28 ppm vs. H3P04,of several of these adducts. It should be noted, however, that only one of these adducts had an electron-withdrawing substituent, namely, a fluorine atom in the para position of t'he phenyl ring. I n all other cases, the substituents were electron-releasing groups or simple alkyl radicals. ;\1arklgreported also the formation of several epoxides from these reactions. However, in all cases, the epoxides were deriued from benzaldehyde and from its derivatives having electron-withdrawing substituents. ;\larkl9 assumed that the 1 : l P-C-0 adducts, XIV, condensed, in all cases, with a second molecule of the (17) F. Ramirez, A. V. Patwardhan, and S. R. Heller, J . A m . Chem. Soc., 86, 514 (1964). (18) (a) R. F. Hudson, "Structure and Mechanisms in Organo-Phosphorus Chemistry," Academic Psess Inc.. New York, N . Y., 1965, Chapters 4 end 5, in particular p 153. This review containn numerous references dealing in particular with the reactions of trialkyl phosphites and of tertiary phosphines with u-halo ketones. (b) F. Ramirez, 0. P. Madan, and C. P. Smith, Teftahedron, l a , 567 (1966). This paper deals with the reactions of trirlkyl phosphites, trisdialkylaminophosphines, and tertiary phosphines with u,O-unsaturated ketones. (c) R.. G . Pearson and J . Songstad, J . Am. Chem. SOC., 89, 1827 (1967j, have discussed nucleophilic substitutions by "hard" and
"soft" bases. (19) V. Mark, ibid., 86, 1884 (1963). (20) For a recent review on this subject. see R. Rurgada, Ann. C h i m . . 13 (1966).
m
R
xv R I + H-C-P(OR),
2
H-$!-P+[N(Cy313,
P
H-C-0 k +k - lc / R
A " (CHdzN I N(CH3)z N(CH3h XVII
XVI
-
R I H- C-
\l-R
0
I
H
+ IPrN(cII,)z]3
xIX
XVIII
It should be emphasized that adducts of type XV, XVI, or XVII were not made from the reactions of the isolated 1: 1 P-C-0 adducts of type XIV.l9 There is no evidence that a 2: 1 adduct with a P-C-0 bond can give rise to an epoxide and an amidate. In the present paper, we will be concerned only with the reactions of trisdialkylaminophosphines with aromatic aldehydes having electron-withdrawing substituents. Subsequent papers will deal with the corresponding reactions of aromatic aldehydes having electron-releasing substituents and with unsubstituted aliphatic monoaldehydes. Results Reaction of the Nitrobenzaldehydes with Trisdia1kylaminophosphines.-p-Nitrobenzaldehyde was allowed to react with 2-N-pyrrolidino-l,3-dimethyl-1,3,2diazaphospholane, XX, in methylene chloride solution a t -70". The solvent was removed after the temperature had reached 20". The crystalline product was isolated in 90% yield and was shown to be a mixture of the two diastereomeric 2,2,2-triamino-l,3,2-dioxaphospholanes, XXIVa and XXIVb. These isomers were formed in the approximate proportion of 2.4:l. The major isomer was obtained in pure form by fractional crystallization; it was assigned the configuration having the two hydrogens on the phospholane ring in the cis relationship as shown in formula XXIVa. This assignment was based on the observation that the two phospholane hydrogens of the major isomer, XXIVa, gave a doublet a t a lower magnetic field ( 7 4.77) and with a larger H1-P31 coupling constant (JHP= 11.0 cps) than the corresponding doublet of the minor isomer, XXIVb ( T 5.54, JHP
