C 0 M MU N I CAT1 0N S a phosphatetrazene isomer equilibrium arising by migration of the (CH3)& group hardly appears likelyl4I. 31P-NMR (20 % solution in C6H6, 85 % H3P04 as external standard): 6 = -321 ppm. (3): colorless crystals, m. p. 65--67°C (b. p. 83-85"C/0.01 torr; yield 25 %), readily soluble in aprotic organic solvents. ,lP-NMR: 6 = -79.2ppm. The NMR data indicate that the compound exists solely in one isomeric form (cis or trans). Procedure:
l-tert-Butyl-3-trirnethylsilyl-4,4-dimethyl2-phospha-1-tetrazene By Otto J. Scherer and Walter Glassel[*] Dedicated to Professor Fritz See1 on the occasion of his 60th birthday Formal replacement of one of the two imine nitrogen atoms in tetrazene derivativedl1 by a phosphorus atom leads to phosphatetrazenes. We have synthesized the first compound of this type :
A - LiCI/-RCl
(1) R = (CH3),Si, R' = (CH&,C
Evidence opposing the formation of the 2-phospha-2-tetrazene isomer, (CH,),N-N=P-NRR', is provided by the findings : 1) The 45,, coupling constants of the isolated product lie in the range found for "phosphatriazenes" RR'N-P=NR (R=(CH3)3Si, R'= R"= (CH3)3C[2a1; R=R'=(CH3)3Si. R"=(CH3)3C[2b1); 2) Attempts at a directed synthesis of the phospha-2-tetrazene (CH,),N-N=P-NR'R" led to a (PN), four-membered ringc3]:
(29.06 g, 200 mmol) in A solution of (CH ,),CNHSi(CH diethyl ether (100ml) is metalated with n-C4H9Li-hexanesolution (124ml,200mmol). The resulting solution is added dropwise with ice cooling to PC13 (26.1g, 190mmol) in ether (300ml), stirred for 1 h at room temperature, and cooled to - 78°C. After addition of (CH3)2N-NLi-Si(CH3)3 [prepared by metalation of (CH3)2N-NH-Si(CH3)3] (200mmol) in ether (100ml), the mixture is stirred for 12h, and then evaporated at water pump vacuum. The residue is taken up in pentane (50 ml) and filtered through a G3 frit. Fractional distillation (Vigreux column) affords 9.41 g (21 % based on PCl,) of ( 2 ) , b. p. 44-45"C/0.01 torr. Received: June 12, 1975 [Z 270 IE] German version: Angew. Chem. 87. 667 (1975) ~-
[l] Both I - and 2-tetrazenes are known. To our knowledge, however, alkyl derivatives exist only in the 2-tetrazene form; cf. N. Wiberg and W Uhlenbrock, Chem. Ber. 105, 63 (1972).  a ) 0. J. Scherer and N. Kuhn, Angew. Chem. 86. 899 (1974); Angew. Chem. internat. Edit. 13. 811 (1974); and references cited therein; b) J. Organometal. Chem. 82, C3 (1974). 131 The product ( 3 ) could also arise from the non-distillable precursor (CH3)2N-NR-PCI-NR'R" by intermolecular elimination of RCI. The assumption of a phosphd-ttetrazene intermediate is. however. supported (R=i-C3H7; by the successful quantitative conversion of R,N-P=NR' R'=(CH3),C) into the four-membered ring dimer: 0.J . Scherer and W Gliissel, to be published.  Experience gained with related amine/imine systems [2a] opposes the occurrence of a (CH3)3Si shift that is still too fast at -70°C. The phospha-2-tetrazene, which could be present a s cis or tram isomer, would have to exist exclusively as one of the two isomeric forms. In the case of ( 2 1 , either the inversion barrier of the imine nitrogen is drastically lowered by the rerr-butyl group [5a]. or the two isomers do not differ in the chemical shift of their proton signals down to -70°C [5b].  a ) Cf. studies on guanidines: H. Kessler and D. Leibfritz, Tetrahedron 26, 1805 (1970); b) cf. N-rert-butylaziridines: F . A. L. Aner and J. M. Osyang, J. Am. Chem. SOC.89, 352 (1967): S. J. Brois, ibid. 89. 4242 ( 1967).
Synthesis of revt-Alkyl-SubstitutedGlycines"] By Ulrich Schollkopf and Rolf Meyerr'l
R = (CH3)3Si R ' = (CH3)3C, R" = CH3
(2): distillable greenish yellow liquid which can be stored for several weeks at room temperature on exclusion of air. In solution the compound can even be exposed to air (open NMR sample tube) for several hours (ca. 10 h) without undergoing significant change. 'H-NMR measurements in toluene down to -70°C revealed no change in the spectrum; thus [*] Prof. Dr. 0. J. Scherer and DipLChem. W. Glassel Fachbereich Chemie der Universitat 675 Kaiserslautern, Postfach 3049 (Germany) Angew. Chem. inrernat. Edit.
Vol. 14 ( 1 9 7 5 ) 1 No. 9
a-Metalated isocyanides"] have already opened up many novel routes to ammo acid^'^,^! We now wish to report a high-yield synthesis of tert-alkyl-substituted glycines [type (4)]. These compounds are employed inter alia in molecular biology in order to delineate the recognition range of tRNA synthetasesc5I. In their synthesis a Grignard reagent (2) is added to the f3-substituted ethyl a-isocyanoacrylates ( 2 )I6]. Hydrolysis yields 3-tert-alkyl-substituted ethyl cx-isocyanoacetates (3) which can readily be converted (as is generally the casei4]) into amino acid derivatives ( 4 ) in good yields. As far as we have yet been able to establish, the yields of the addition [*] Prof. Dr. U. Schollkopf and Dipl.-Chem. R. Meyer Organisch-Chemisches Institut der Universitat 34 Gottingen, Windausweg 2 (Germany)