5-carboxylic esters in the proportions 76: 24 (70:30 on addition of benzonitrile oxide to cinnamic ester L4J). By virtue of the angular strain of its double bond, norbornene reacts with (2) to give 16 % of the adduct (12), b.p. 65-75 "C/ 0.001 mm [NMR (CDCI3): P = 3.08 (H-3, d), J33a = 1 Hz; 7 - 6.85 (H-3a, q), J3a7a = 8.2 Hz; P = 5.61 (H-7a, d). The absence of coupling of H-3a and H-7a with the bridge- head hydrogen proves the exo-addition. Triethylamine converts (12) into the nitrile (13) [m.p. 35-38°C; I R : 2270 (C-N), 3450 cm-* (OH)] in 93 "/, yield, but only after boiling for 12 h.

Cyclopentene and (2) give (14) in 8 % yield (b.p. 95-11OoC (bath)/lO mm). The adduct (IS) of cyclooctatetraene, also isolated in 8 % yield, is derived from the bicyclo[4.2.0]- octadiene skeleton, as is shown by the ratio of vinyl-H to

tertiary-5-Phenyl-2-isoxazoline (16) (b.p. 90-100 "C/O.OOl mm) is formed in 70% yield by cycloaddition of (2) to styrene. Its N M R spectrum (CDC13) proves the structure: P = 2.91 (H-3, to J34 := 1.7 Hz; the CH2 group on C-4 provides the expected 16-line signal (J,,, = -17.6 Hz). Ring opening to give the hydroxynitrile occurs only in boiling triethylamine.

The norbornadiene adduct (17), which is isolated by distilla- tion (b.p. 60-65"C/0.001 mm) in 41 % yield and whose structure is proved by NMR and IR spectra, undergoes a retro-Diels-Alder reaction at 140-160 O C , which leads to cyclopentadiene and isoxazole (90 % yield). N M R spec- trum of (18) (CDC13): P = 1.66 (H-3, d), P = 3.59 (H-4, t), and P = 1.49 (H-5, d) with J34 = J 4 5 = 1.5 Hz.

H a

H R (18) R = H (19) R = C6H5

Reaction of (2) with phenylacetylene gives a 51 % yield of 5-phenylisoxazole (19). N M R (CDCI3): T = 1.72 (H-3, d) and P = 3.52 (H-4, d) with J34 = 1.9 Hz.

Methyl propiolate adds fulminic acid in both directions. A 84: 16 mixture of (20), m.p. 47-50 "C 151, and (21) is obtained in 50 "/, yield. N M R spectrum of (20) (CDCI3): T = 1.47 and 2.93 (H-3 and H-4, d) with 534 = 1.8 Hz, P = 5.98 (OCH,,s). N M R spectrum of (21) (CDC13): T = 1.30 (H-3, s), P = 0.85 (H-5, s), and T = 6.09 (OCH3, s). Benzonitrile oxide reacts with methylpropiolate, giving the 5- and the 4-carboxylic ester in the ratio 72: 28 [41.

These cycloadditions are incompatible with the classical carboxime formula but agree with the formonitrile oxide structure of fulminic acid, thus supporting a recent assign- ment [61 based on IR spectroscopy.

Received: March ZOth, 1967 [Z 478 IE] German version: Angew. Chern. 79, 471 (1967)

[*I Prof. R. Huisgen and Dip1.-Chem. M. Christ1 Institut fur Organische Chemie der Universitit Karlstr. 23 8 Munchen 2 (Germany)

111 A . Quilico and G. Stagno d'Aleontres, Gazz. chim. ital. 79, 654, 703 (1949).

[2] G. Stagno d'Alcantres and G. Fetiech, Gazz. chim. itai. 82, 175 (1952). [3] A . Quilico and L. Panizzi, Gazz. chim. ital. 72, 155 (1942). [4] R . Sustmann, Dissertation, Universitat Miinchen, 1965. [5] Synthesis by another method: A. Quilico and L. Potiizzi, Gazz. chim. ital. 72, 458 (1942); M.p. 49-50°C. [6] W. Beck and K . Feldl, Angew. Chem. 78, 746 (1966); Angew. Chem. internat. Edit. 5, 525 (1966).

1,3-Cycloadditions of Nitrones to Methylenephosphoranes

By J. Wulff and R. Huisgen[*l

It has recently been shown that methylenephosphoranes are dipolarophiles and combine with nitrile oxides to give five- membered cycloadducts [ I , *]. We have chosen azomethine oxides (nitrones) for further investigations since they represent a class of 1,3-dipoles that contain no double bond in their sextet structure [31.

(a), R = R' = H

(b) , R = R' = D (c ) , R = C6H5, R' = H (d), R = R' = CH,

If one equivalent each of C,N-diphenylnitrone (1) and methylenetriphenylphosphorane (2n) are mixed in ether at 20 OC, the colorless, crystalline 1,2,5-oxazaphosphole deriva- tive (30) precipitates in 93 % yield (decomp. 136-137 "C); C, H, and N analyses and osmometric determination of the molecular weight give correct values for (30) as well as for the otlier new compounds prepared. N M R spectrum (CDC13) of ( 3 ~ ) : H-4 and H-4' as octuplets a t P = 6.36 and 6.93 with J44, = -16.3, J34 = 8.5, J 4 5 = 12.0, J34, = 7.0, and J4'5 =

12.4 Hz. The similarity of the couplings of H-3 (J35 = 8.1 Hz) leads to a quadruple! at P = 5.30. The 31P signal at +58.6 ppm (CDC13, 85 % phosphoric acid as external standard) indicates quinquecovalent phosphorus; if the phosphonium zwitterion ( 4 ) were present instead of the isomeric (3a), then a large negative chemical shift would be observed [41.

The IH-NMR spectrum could be interpreted only by comparison with that of the 4,4-dideuterio compound (3b). The compound (2b) is obtained from (trideuteriomethy1)- triphenylphosphonium bromide by reaction with sodamide in benzene151 without D-exchange. N M R spectrum (CDCI3) of (3b) : H-3 as broad doublet at P = 5.32 with J35 = 8.1 Hz.

Hydrolysis of (30) in dioxane / water ( 5 : 1 v/v) at 100 "C gives (I ,2-diphenylethyl)diphenylphosphine oxide (5) (yield 81 %) identified by comparison with an authentic specimen 161. The N-phenylhydroxylamine that is also expected can be isolated

Angew. Chem. internat. Edit. / Voi. 6 (1967) 1 No. 5 457

as C,N-diphenylnitrone if the hydrolysis is conducted in the presence of benzaldehyde. The reaction route leading to (5) [(6) is conceivable as intermediate] is as far from clear, as is the formation of(5) from a methyltriphenylphosphonium salt and benzaldehyde in the presence of sodium ethoxide in ethanol 171.

7sH5 y6H5

Thermolysis of (3.) in boiling xylene, which occurs with formal loss of benzyne and formation of (7a) in 38 % yield, is also not understood; m.p. 204-205 OC; IR spectrum (KBr): 3320 (NH) and 1182 cm-1 (P=O). In an independent syn- thesis of (7a) (91 % yield), the zwitterion obtained from (217) and N-benzylideneaniline in ether is hydrolysed.

Slow reaction of benzylidenetriphenylphosphorane (2c) with ( I ) in benzene at 60°C for 24 h gives the cycloadduct (3c) in 39 % yield, (decomp. 146-147 "C). N M R spectrum (CDC13): r = 5.13 (H-3, t) with 534 = J35 = 6.5 Hz, and T =

5.67 (H-4, q) with J45 = 10.0 Hz; the 3lP signal (CDCl3) is at +57.9 ppm. Thermolysis of (312) in xylene gives the phos- phine oxide (7c) in 24 %yield, m.p. 228-229 OC; I R spectrum (KBr): 3360 (NH) and 1178 cm-1 tP=O). . ,

Isopropylidenetriphenylphosphorane (2d) also adds ( I ) in ether at 20 "C. The adduct (3d) (yield 22 %, decomp. 142 to 143 "C), is isolated along with 15 % of triphenylphosphine. NMRspectrum (CDC4) of (3d): t = 9.09 (4-CH3, d) with J45 = 21 Hz, T = 8.37 (4'-CH3) with J4'5 = 18 Hz, and T = 5.01 (H-3, s); 31P signal (CDC13) + 46.3 ppm. Hydrolysis of (3d) in boiling dioxane/water (10:3 v/v), or pyrolysis in a high vacuum at 150 "C, leads to the same product (7d). (2-Anilino- 1,l-dimethy1phenethyl)diphenylphosphine oxide melts at 217-219OC and is identical with a product which was obtained from (2d) and N-benzylideneaniline with subse- quent hydrolysis. N M R spectrum (CDC13) of (7d) : 7 = 8.69 (CH3, d) with J = 14 Hz, T = 8.89 (CH3, d) with J = 16 Hz, T = 5.84 (tertiary H , d, broad) with J = 7.0 Hz, IR band (KBr) at 3320 cm-1 (NH). N-Methyl-C-phenylnitrone reacts more slowly than (1 ) with methylenetriphenylphosphorane (2a) in ether. The resulting cycloadduct (analogous to (30), N-CH3 instead of N-C&s) melts at 134-135 'C; 31P signal (CDCI3): + 60.3 ppm- Hy- drolysis with dioxane/water gives the same phosphine oxide (5) (yield 43 %) as is formed from (3a).

1,3-Dipolar cycloaddition of 3,4-dihydroisoquinoline N-oxide (9) to ethyl crotonate at 100 "C is 43 times faster than that of C,N-diphenylnitrone ( I ) [a]. The nitrone (9), however, combines more slowly with (2a) than does ( I ) ; after a week in benzene at room temperature (IOa) (73 % yield, m.p. 146-147 "C, 31P signal (CDC13)- +56.4 ppm) is isolated.

Hydrolysis of (lOa) in boiling dioxane/water is accompanied by fragmentation to starting materials, yielding, alongside (9), 78 % of methyldiphenylphosphine oxide which is a

known hydrolysis product of (2.). If ( ion) is heated in the presence of benzaldehyde in anhydrous ethanol, (1 ,Z-di- pheny1ethyl)diphenylphosphine oxide (5 ) is formed in 48 % yield by the route described by Trippett and Walker[71 i.e. via (Za). The N-oxide (9) can be recovered to the extent of 70 ?< after being boiled for threc days with benzylidenetriphenylphos- phorane (2c) in benzene. 81 % of the ( 9 ) consumed appears as the colorless cycloadduct (lob), decomp. 150-152 OC; NMR spectrum (CDCIj), T = 5.24 and 5.80 (2 tertiary H, q); the ABX spectrum shows the J values 5.4, 15.0, and 15.5 Hz; 3IP signal (CDC13): +50.9 ppm.

Received: March 28th. 1967 [Z 480 IE] German version: Angew. Chem. 7Y, 472 (1967)

[*] Dip1.-Chem. J. Wulff and Prof. R. Huisgen Institut fur Organische Chemie der Universitat Karlstr. 23 8 Munchen 2 (Germany)

[l] R. Huisgen and J. Wulff, Tetrahedron Letters 1967, 917. [2] H. J. Bestmann and H. Kunslmann, Angew. Chem. 78, 1059 (1966); Angew. Chem. internat. Edit. 5 , 1039 (1966). [3] For classification of 1,3-dipoles see R. Huisgen, Angew. Chem. 75,604 (1963); Angew. Chem. internat. Edit. 2,565 (1963). 141 E. Fluck: Die kernmagnetische Resonanz und ihre Anwen- dung in der Anorganischen Chemie. Springer, Berlin 1963, p. 197. [5] G. Wittig and H. Pommer, German Pat. 1003730 (BASF); Chem. Abstr. 53, 16063 (1959). [6] L. Horner and P . Beck, Chern. Ber. 93, 1371 (1960). [7] S.Trippett and D. J. Walker, Chem. Commun. 1965, 106. [8] H . Seidl, Dissertation, Universitat Miinchen 1964, p. 50.

A New Synthesis of Phosphabenzene Derivatives

By G. MarkI, F. Lieb, and A . Merz[*]

It is usualty impossible to isolate the phosphonium salts that are formed from silylphosphines and alkyl halides since they readily decompose into alkylphosphines and halosilanes[*l. Thus the reaction of tris(trimethy1silyl)phosphine [2J ( I ) with pyrylium iodides (fluoroborates and perchlorates cannot be used because of the low nucleophilicity of the anions) gives iodotrimethylsilane and the bis(trirnethylsily1)phosphine (2) 131; however, the latter is not isolated but cyclizes with separation of hexarnethyldisiloxane and formation of the substituted phosphabenzene (3) .

J "3

458 Angew. Chem. internat. Edit. / VoI. 6 (1967) / No. 5