8224
predominate for 4b.I7 However, 4a can assume the strong evidence has been reported for the greater therconformation 9 in which pr-dr stabilization is maximal. modynamic stability of configuration a compared to Thus, normal vicinal interactions which give rise to b for I and II.1-3 While the bulk of the reported evithe axial preference for other substituentslj2 may be dence supports the same phosphorus stereochemistry outweighed by the conjugative effects available in 9. for several analogous systems, there have been reports We recognize that pr-d, bonding is likely to be concontending for the greater stability of equatorial alkoxy siderably reduced in a molecule such as 4, which is substituents. Although IIIa and b closely resemble more similar to (MeO)zPNMen than to Me,NPF,. It Ia and b, we present in this communication evidence seems likely nonetheless that the conformational prefthat the b isomer of the latter compound is the more erence peculiar to the Me2N is in some way related to thermodynamically stable as is also very probably the the presence of the lone pair on nitrogen and its intercase for IVa and b.5 action with the orbitals, occupied or empty, on phosPentavalent phosphorus a and b isomers where X = phorus. Id 0 are also known and the stereochemistry at phosThat lone-pair orientation at phosphorus may phorus has been deduced from nmr results in solution affect 3 J I ~ e was s ~ suggestedlg earlier. Our results apand X-ray diffraction experiments in the solid state.6 pear to be the first to substantiate the idea that 3JHc0p In the vast majority of cases where R = aryl, alkyl, depends on both the HCOP dihedral angle (Karplusor alkoxy, the P=O group prefers the equatorial posilike relation) and the phosphorus lone-pair orientation although chair-chair and chair-boat equilibria in tion. This approach may in fact turn out to be a solution can occur to varying degrees.6 The prefervery powerful one indeed for assignment of substituent ence of the P=O group to be equatorially disposed configuration at trivalent phosphorus in 1,3,2-dioxahas also recently been shown when R1 is H in Va,b phosphorinanes. and VIa,b.2 In this communication we report the isolation and the phosphorus stereochemical assignAcknowledgment. This work was supported by a ments of the a and b isomers of VI1 and VIII. grant from the National Science Foundation (GPThe first steps in reactions 1 and 2 each produce a 22885). 86O
(17) 1,3-Interactions in 8 may be relieved to some degree by ring reversal to the alternate chain with Me2N equatorial or the analogous boat or twist form with Me2N pseudoequatorial in which p--d, bonding would be available. (18) E.g., a referee has suggested that the MezN in 7 and 9 may be pyramidal and that a stabilizing lone pair-lone pair gauche effect available to 9 is responsible for its lower energy. (19) D. Gagnaire and J. B. Robert, Bull. SOC.Chim. Fr., 2240 (1967).
P(NMe&
+ rneso-(HOCHMe)2CH2--+ -2HSlle!
Wesley G . Bentrude,* Han Wan Tan Department of Chemistry, Uninicersity of Utah Salt Lake C i t y , Utah 84112 Receiced Jurie 14, 1972
Phosphorus Stereochemistries in Isomeric 2-Dimethylamino-l,3,2-dioxaphosphorinanes
Sir : The factors governing the relative stabilities of the two possible configurations a and b at phosphorus in cyclic six-membered ring systems have received significant attention in a number of laboratories recently. In trivalent phosphorus systems (X = lone pair (Ip))
C1 IIIn
+
IIIb
1
:
10
I
X
Ia
lp
IIa
!p
IIIa
Ip
n7a
Va VIa \'Ha VIIIa
IXa
xn
ip
0 0 0 0 0 0
R,
x
R.
OMe Me Ohle H KMe Me Nhle. H Me H H H 9 M e - Me
Ib
IP
IIb
!P
IIIb
!P
IVb
1P
Vb VIb VI1b VIII~
0 0 0
NMe, 0lle
H Me
IXb
0 0
031~
H
Xh
0
Journal of the American Chemical Society
VIIa
1
0
+
(2)
YIIb
: 10
VIlb , VIIIb 2
+ :
VIIa 1
i
3
+
YIh : 1
phosphorus systems in greater than 60 % yield although the b to a ratio is now 2: 1 as revealed from integration of the pmr spectra. The isomers of VI1 and VI11 can
I
x
r\O
10: 1 ratio of IIIb to IIIa in overall yields exceeding 6 0 z as shown by their pmr spectra, details of which will be published in due course. Pmr spectra also show that this ratio is preserved in the stereospecific and nearly quantitative oxidation to VIIb and VIIa. Reaction scheme 3 produces the indicated pentavalent
ref1
R,
+
RI
R-
OMe OMe
Me H
XMe, &le NMe, H H Me H
H
&Me, Me NMe? H Ohle Me OMe H 1
(1) J. Rodgers, D. W. White, and J. G. Verkade, J . Chem. SOC.A , 77 (1971). (2) J. A. Mosbo and J. G. Verkade, J . Amer. Chem. Soc.. in press. (3) M. G. B. Drew, J. Rodgers, D. W. White, and J. G. Verkadr, J . Chem. SOC.D , 227 (1971). (4) See D. W. White, R. D. Bertrand, G. I
