Nov. 5, 1959
CO~IMUNICATIOXS TO THE EDITOR
5833
Rlonohydroboration occurs rnore readily with non-conjugated dienes and the conjugated dienes of cyclic systems. Thus treatment of a-terpinene and cyclohexadiene with diborane results in the utilization of nearly six moles of diene per niole of diborane. Similarly, 1,j-hexadiene is transformed readily into 5-hexen-1-01, b.p. 78-80' at 25 mm., n 2 ' D 1.4355, a-naphthylurethane, m.p. G3-64", and bicycloheptadiene into exo-dehydronorborneol. Bicycloheptadiene, 18.4 g., 0.2 mole (lOOyo excess), and 25 mrnole of lithium borohydride in 25 ml. of ether a t 0" was treated with 4.6 g., 33 mmoles, of boron trifluoride etherate over 30 minutes. -4fter 1 hour at room temperature, the ether and excess diene were removed under vacuum, ether added, and the oxidation performed. Vapor phase chromatography examination indicated the formation of 63% dehydronorborneol (SSY0 exo-, 12% endo-). The solid product was pressed on a porous plate, recrystallized and sublimed, 4.9 g., -25y6, m.p. 92-93", phenylurethane, m.p. 156-158".
14,54O),there was obtained an alcohol product which was at least very predominantly thrco. Reaction of the crude product with phthalic anhydride in pyridine gave a 77y0 yield (over-all based on olefin) of tlzrco-3-p-anisyl-2-butyl acid phthalate, m.p. 122-123.5" after a single recrystallization, mixed m.p. with authentic material4 123-124'. In neither case was any benzyl alcohol detected. As regards orientation in the over-all hydration of the double bond, the observed results with cyclopentadiene and the 2-anisyl-2-butenes were those anticipated on the basis of the reported results with unsymmetrical olefins2 and ~ t y r e n e . ~ These results suggest that the hydroborationoxidation method is a promising one for preparation 01 homoallyl alcohols from conjugated dienes and homobenzyl alcohols from conjugated aryl olefins.'j Regarding the stereochemistry of the over-all hydration of the double bond by hydroborationoxidation, the present results illustrate for the cis- and trczns-2-p-anisyl-2-butenes the stereoRICHARD B WETHERILL LABORATORY PURDUE UNIVERSITY HERBERT C. BROWN specific cis-addition already demonstrated in aliLAFAYETTE, INDIANA GEORGEZTVEIFEL cyclic case^.^,^ The new method, therefore, is RECEIVED SEPTEMBER 24, 1959 very convenient for the preparation of pure diastereomeric alcohols from olefins similar to the 2-9-anisyl-2-butenes. Especially for the threo-3HOMOALLYL AND HOMOBENZYL ALCOHOLS anisy:-2-butanolJ this method is a distinct improveBY T H E HYDROBORATION METHOD' ment over the conventional one formerly en:Sir: IVe wish to report that H. C. Brown's elegant ployed. These and other results will be reported in greater hydroboration-oxidation method2 for hydrating olefins provides an especially convenient route to detail e l s e ~ h e r e . ~ (5) H . C. Brown a n d B. C. Subba Rao, J . Org. Chem., 22, 113G homoallyl and diastereomeric homobenzyl alco(1957). hols. (6) T h e degree of alkyl substitution of the olefin is important. F o r Hydroboration of cyclopentadiene was carried example, hydroboration-oxidation of anethole gives a 7 5 :2 5 mixture out by the general method of Brown and Zweifel,2 of 1-p-anisyl-1-propanol a n d l-~-anisyl-2-propano1.* (7) (a) W. J. Wechter, Chemislry and Indilstry, 294 (1959); (b) S. except t h a t a 7070 molar excess of diene was emhf. Nussim, Y. hfazur a n d F. Sondheimer, J . O r g . Chem., 24, ployed in order to minimize glycol formation. Wolfe, 1034 (1959). Under these conditions, a 30% yield of A3-cyclo- DEPARTMEKT OF CHEXISTRY S. WINSTEIN pentenol was isolated; b.p. 67-68' (36 mni.), UXIVERSITY OF CALIFORNIA EVANL. ALLRED Los AXGELES 24, CALIF. JOSEPH SOSNENBERG n 2 ' D 1.4673, phenylurethan, m.p. 140.4-140.8", mixed m.p. with authentic material3 140.4-141 .0", RECEIVED SEPTEMBER 24, 1959 ptoluenesulfonate (SOY0 yield), m.p. 53.4-54.2", mixed m.p. with authentic material3 53.2-54.2'. PROBABLE STRUCTURE OF T H E BioHlo-' ION Infrared and vapor phase chromatographic analysis Sir : showed the alcohol product to be very predomiThe presence of B l ~ H l ~ -ion1 2 in "ionic Blonantly A3-cyclopentenol, less than 1% A?-cycloH12R2," where R is an electron donor such as pentenol being present. Treatment of tran~-2-P-anisyl-2-butene,~ b.p. hIeJY, has now been substantiated by the preparaInfrared spectra indi103" (10 mm.), Z"D 1.5316, Xmax 243 m p (E 10,- tion of BloHlo(KMe4)2. cated no BH? groups, no BHB bridges and were with diborane, followed by oxidation with alkaline hydrogen peroxide according to the consistent with the presence of discrete NMe: procedure of Brown and Zweifel,' resulted in a 72y0 ions. The n.m.r. B" spectrum showed oniy a yield of almost pure crythro-3-p-anisyl-2-butanol,low field doublet and a high field doublet of area m.p. 58.5-50.5" after one recrystallization, mixed about four times that of the low field doublet. No satisfactory valence structure based on sernim.p. with authentic material4 59.5-60". Similarly, from hydration of cis-2-p-anisyl-2-butene, b.p. localized three-center bonds in the low symmetry Blo framework of B10H14 has been found.2 On 117.5" (10 mm.), T L ~ ~1.5195, D Amax 252 mu ( E the other hand, a molecule of high symmetry is (1) (a) This research was supported in p a r t b y a g r a n t from T h e suggested by the n.m.r. results. A simple BloPetroleum Research F u n d administered b y t h e American Chemical H ~ o polyhedron, -~ closely related in structure to Society. Grateful acknowledgment is hereby made t o t h e donors of this f u n d ; (b) research supported i n p a r t by the Xational Science B5H9 and based on satisfactory molecular orbitals, Foundation. has been discovered. (2) H . C. Brown a n d G. Zweifel, THISJOURNAL, 81, 247 (1959). (3) E. L. Allred, J. Sonnenberg a n d S.Winstein, J . Org. Chem., in press. (4) S. Winstein and G. C. Robinson, THISJOURNAL, SO, 169 (1958).
(1) M. F. Hawthorne and A. R. Pitochelli, THIS JOURNAL, t o be published.
(2) J. Reddy a n d W. pi. Lipscomb, J. Chem. P h y s . , 31, 610 (1959).
583.1
COMMUKICATIOKS TO THE EDITOR
H
YH Fig. 1.-Proposed structure of the B l ~ H I ~ ion - 2 viewed approximately along the S axis.
The molecular structure (Fig. I) has only two kinds of boron atoms in the ratio of 2 (apex) to S (approximately equatorial) in a polyhedron of symmetry D i d . The valence orbitals of the apical boron atoms are slightly less symmetrical than those of the equatorial boron atoms, and hence the temperature-independent paramagnetism should be slightly greater for the apical boron atoms. This explanation, based upon a choice of origin a t the boron nucleus, forms a more satisfactory basis for understanding B" resonance shifts than t h a t based strictly on formal charge and diamagnetism. Thus the n.m.r. results are well satisfied . The valence orbitals can best be described by recognition of the two B5Hj groups, like those in BjHg molecules, with almost equatorial boron atoms replacing bridge hydrogens. Of t.he twentyone electron pairs, ten are used for B H single bonds, and three for each of the framework B j groups like those3 in RjHq, and five for bonding among the sixteen remaining sp3 orbitals of the eight almost equatorial B atoms. In D.ld these sixteen orbitals have the representation XI -t A? B1 f B? 2E1 2E2 2Ea. Assuming all close interactions as the same, we find3 Alla t I-Io 28, E?,at Ho (2 2'ir)'/?,B and Fd l at. Ho %'/2/3 as strongly bonding orbitals to be occupied by these five electron pairs. The very weakly bonding E2 a t Ho + (2 - .)'/?)'/'$ and non-bonding R1 and B?, as well as all of the antibonding orbitals are unfilled. Thus AI0 theory in its simplest form leads to a closed shell electronic structure for BloHlc-'.
+
+
+
+ + +
1'01. SI
tional w0rk.l Other methods, catalytic and chemical, of reductive C-S cleavage have had limited utility. Hydrazine with or without alkali has been found to desulfurize cyclic or acylic dithioketals. Xlthough the full scope and mechanism of this reaction has not as yet been established, preliminary results indicate satisfactory yields (60EW?
