4667 Experimental Section Mass Spectra. Low-resolution mass spectra were recorded using an Atlas CH4 instrument equipped with a TO4 direct inlet source and the high-temperature inlet system. High-resolution mass measurements were performed by peak matching using two MS-9 instruments employing the direct insertion system. Source temperatures on the two instruments were 180-200 and 200-
mle 171
+
230'. Deuterated Tolbutamide. Sodium tolbutamide was dissolved in DzOand concentrated by evaporation of solvent. Additional DzO
-He
[CaH,No]+ n m/e 98
[C,H,NO]i i m / e 99
scheme were assessed from the mle 107 and 108 peaks rather than from the mle 99 peak.
was added to bring the solution to the original volume and the solution was again concentrated. This process was repeated four times. The solution was then acidified with DCl and the deuterated tolbutamide was filtered, washed with D20,and dried overnight at 50" under high vacuum. The nmr spectrum of this material showed about equal absorptions assigned to both types of N-H groups in this molecule.
4,4,6-Trimethyl-1,3,2-dioxaborinane. A Stable Dialkoxyborane William G. Woods and Philip L. Strong
Contribution from the U;S. Borax Research Corporation, Anaheim, California. Received June 20,1966 Abstract: 4,4,6-Trimethyl-l,3,2-dioxaborinane (5) was prepared by reduction of the 2-chloro derivative (4) with sodium borohydride or lithium aluminum hydride, and from reaction of diborane and tris(2-methyl-2,4-pentanedio1)biborate (6). Five-bond HCCOBH proton-proton coupling (J = 1.6 cps) was observed for 5, but disappeared in the nmr spectrum of the 2-d compound. Hydroborations of cyclohexene, 1-octene, and allyl methyl sul-
fide with 5 gave the corresponding 2-alkyl compounds; 5 gave exclusively terminal addition with 1-alkenes and with 1-alkynes. The nmr spectra of the 1-alkene-1-boronates (11 and 12)from 5 with 1-hexyne and 1-heptyne constitute direct evidence for stereospecific cis addition in the hydroboration of acetylenes. A selective Raney nickel type hydrogenation catalyst was produced from nickel acetate and 5. Reaction of 5 with dimethylamine gave the 2-dimethylamino derivative (14) and with ammonia gave the bis-2-amino compound (13); trimethylamine did not form a complex with 5.
stability is exhibited I nteresting rimethyl-l,3,2-dioxaborinane
by 2-vinyl-4,4,6with respect to other ethyleneboronates. Evidence from our laboratories indicates unusual stability associated with other 2substituted 4,4,6-trimethyl- 1,3,2-dioxaborinanes. Consequently, it was of interest to prepare 4,4,6-trimethyllJ3,2-dioxaborinane (5), the parent member of this system. The instability of dimethoxyborane3 (l), 1,3,2-dio~aborolane~(2a), and 1,3,2-dioxaborinane5 (2b) toward disproportionation has been well documented (see eq 1 and 2). The extent to which 5 is stabilized toward disproportionation, therefore, was of prime concern. 6(CHaO)zBH e4(CH30)3B 1
Synthesis.
+ BzH8
O----(CHa),---i) 2 a,n = 2
b,n
=
3
3
in tetraglyme (eq 3). The yield based on 4 was near c1
+
(1)
NaBH4
4,4,6-TrimethyI- 1,3,2-dioxaborinane (5)
was prepared from 2-chloro-4,4,6-trimethyl-1,3,2-dioxaborinane (4) by reduction with sodium borohydride (1) W. G. Woods, I. S. Bengelsdorf, and D. L. Hunter, J. Org. Chem., 31, 2766 (1966). (2) (a) -W. G . Woods and I. S. Bengelsdorf, [bid., 31, 2769 (1966); (b) W. G. Woods and P. L. Strong, J . Organometal. Chem., in press. (3) A. B. Burg and H. I. Schlesinger, J. Am. Chem. Soc., 55, 4020 (1933). (4) S. H. Rose and S.G. Shore, Inorg. Chem., 1,744 (1962).
( 5 ) G . E. McAchran, Ph.D. Thesis, Ohio State University, 1964.
4
4-
0.5 B2He
4- NaCI
(3)
5 p : o 3
"
5
Woods, Strong J 4,4,6-Trirnethyl-I,3,2-dioxaborinane
4668
50%, whether 1 or 0.5 molar equiv of sodium borohydride was employed. Prior distillation of 4 is not required; material prepared in situ from boron trichloride and tris(2-methyl-2,4-pentanediol)biborate(6) may be used directly (eq 4).6 Lithium aluminum
splitting of each member of the quartet (J = 1.58 cps) is observed (see Figure 1B). Such five-bond protonproton couplings in oxygenated, saturated systems have been reported. 11,12 4-Phenyl-1,3-dioxane shows an equatorial-equatorial HCOCCH coupling of 0.9 cps. 11 Values for the rigid 2,8,9-trioxaadamantane (1.25 cps) and 2,6,7-trioxabicyclo[2.2. Iloctane (1.7 cps) are somewhat higher.I2 The conformational rigidity of 5 might contribute to the enhanced coupling compared with 4-phenyl-1,3-dioxane. In addition, a boron atom with 6 a vacant 2p orbital may be a better transmitter of through-bond, long-range coupling than a saturated carbon aiom. Stability. In contrast to the previously known dialkoxyboranes, 5 is a colorlesss liquid which shows 4 marked stability toward disproportionation. Rose hydride reduction of 4 in bis(2-ethoxyethyl) ether proand Shore4 noted strong absorption due to diborane in vided only a 17 % yield of 5. The stoichiometry (eq 5) the infrared spectrum of all samples of 2a. Diborane was designed to utilize all of the hydridic hydrogen absorptions are barely detectable in the infrared specin this case. A similar reduction of 4 with lithium trum of 5 after 24 hr at room temperature, with no appreciable increase after 48 hr. Whereas 5 can be 4 + 1/4LiA1H4+5 1/4LiAlC14 (5) distilled without disproportionation at 50” (50 mm), aluminum deuteride at a lower temperature and over a longer period provided 4,4,6-trimethyl-1,3,2-dioxa- and with only slight disproportionation at 118-124” (760 mm), 1 , s 2a,4 and 2bS must be handled under borinane-2-d(7) in comparable yield (21 %). vacuum below room temperature. At ambient temAn alternative route to 5 from diborane and 6 was perature, 2a forms a glassy solid4 and 1 is converted to suggested by the isolation of pure 2b (unspecified yield) trimethylborate, whereas 5 remains unchanged after by the reverse of reaction 2.j Only 7 % of 5 resulted 1 month. These results suggest that the equilibrium when diborane was generated in situ from sodium between 5, diborane, and 6 strongly favors 5 . The borohydride and acetic acid7 in the presence of 6. An low yields of 5 realized from treatment of 6 with improved yield (14 %) resulted when excess diborane diborane probably were due to failure to achieve was passed through an ethereal solution of 6 at atmosequilibrium. pheric pressure. Hydroboration Reactions. Selectivity and reduced Characterization. Dioxaborinane 5 was identified reactivity of 5 relative to diborane or alkylboranes was by its elemental analysis, molecular weight (monomer), anticipated due to back T bonding from oxygen to and infrared and nmr spectra. The BH stretching freboron. Hydroboration of 1-octene with 5 at 100” quency of 5 (2550 cm-’) and the B-D of 7 (1901 cm-’) proceeded to give addition of boron at the terminal are as expected for dialkoxyboranes.s Proton nmr position ( 2 8 z yield); 8 was the only observable spectra of 4, 5, and 7 are quite diagnostic. The methyl product. The nmr spectrum exhibits a multiplet groups at C-4 appear as a sharp singlet near r 8.7, while that at C - 6 (equatorial) records as a doublet ( r 8.8, 5 H~C=CH(CH~)SCH~ J = 6 cps). The C - 6 proton (axial) is a complex multiplet of at least 13 lines centered near r 5.6 in 4 and 7 5.8 in 5 and 7. The proton on the boron atom of 5 was located with difficulty as a broad quartet centered near 3 cps. The latter is in excellent 7 6.3 with JBH = 173 agreement with the JBH value of 171 cps found in the boron-11 spectrum of 2b.j The methylene protons at C-5 comprise the AB portion of an ABX system in the r 7.9-8.4 region. Long-Range Coupling. The low-field portion of the upfield from the main absorption which is assigned to C-5 methylene muItiplet for 4 and 7 consists of a quartet. the two hydrogens adjacent to boron. No multiplet This quartet, shown for 7 in Figure lA, is assigned to for a tertiary hydrogen as expected for 9 is observed. the equatorial proton at C-5. The coupling constant Terminal addition with the bulky 5 is not surprising with the axial proton at C-6 is 3.6 cps, in agreement since di~iamylborane’~ gives 99 of the terminal with the reported values for vicinal axial-equatorial adduct. Similar results were obtained in the hydrocoupling in 1,3-dio~anes.~A geminal coupling conboration of allyl methyl sulfide which gave 2-[l-(4stant of J = 14.1 cps for the C-5 methylene group of 5 thiapentyl)]-4,4,6-trimethyl-I, 3,2-dioxaborinane (1 0). is in the expected range.*O In the case of 5, a further
+
+
(6) G. H. Birum and J. L. Dever (to Monsanto Chemical Co.), U.S . Patent 3,064,032 (1962). (7) H. C. Brown, E. J. Mead, and C. J. Shoaf, J . A m . Chem. SOC.,78, 3613 (1956). (8) H. Steinberg, “Organoboron Chemistry,” Vol. I, Interscience Publishers, Inc., New York, N. Y . , 1964, p 871. (9) (a) C. Barbier, J. Delrnan, and J. Rauft, Tetrahedron Letters, N o . 45, 3339 (1964); (b) J. Delrnan and C. Barbier, J . Chem. Phys., 41, 1106 (1964).
Journal o j t h e American Chemical Society
/
88:20
---+
(10) L. M. Jackman, “Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry,” Pergamon Press, Inc., New York,
N. Y . , 1959, p 85. (11) K. C. Ramey and J. Messick, Tetrahedron Letters, No. 49, 4423 (1956). (12)
E. J. Boros, I
