6792
OTHP
J(15N-H), and hence the nitrogen hybridization, on trimethylsilylation of [ 15N]aniline. Similarly, nmr experiments6 designed to evaluate the transmission of substituent effects through the N-Si-N system in silaimidazolidines did not reveal any differences from the analogous carbon system (N-C-N), and the force constant of the Si-N bond is more consistent with single than with double bond character.' We have now VI , h - H , R = (22R)-CH(OH)C&C(CH&OTHP measured the electronic absorption spectra of selected b, 5@-H,R (22R)-CH(OH)C&C(CH&OTHP C, 5@-H,R = (~~R)-CH(OH)CHZCH~C(CHB)ZOTHP aminosilanes and have found this to be a fruitful approach to the understanding of the nature of the (p + acid hydrolysis of the protecting groups of VIc and chrod)n Si-N bond. matographic purification of the product afforded In contrast to alkyl substitution,* stepwise silylation crustecdysone (Ia) [mp 24Ck242' (from methanol-ethyl of ammonia results in a progressive hypsochromic shift 1656, 1615, acetate); A:","," 240 mp ( E 12,670); ::v of the absorption maxima (Table I). The transparency 1387, 1229, 1053, 917, and 878 cm-l; nmr (pyridine-&) 1.07 (19-H), 1.20 (18-H), 1.36 (26- and 27-H), 1.56 (21Table I. Absorption Maxima and Basicities of Aminosilanes H), and 6.17 (7-H)]. A mixture melting point with authentic crustecdyCompd e Av,*Cm-' A,,,, mpa sone'j (mp 247-248') showed no depression. The two Et3SiNH2 208.8 1780 38 samples were identical in spectroscopic16 and chromato(Et3S&NH 205.5 e 1810 graphic behavior and biological activity in Samia (Me3Si)*NH 203.7 2870 30d cynthia silkmoth assay for moulting hormone activity. 202.6~ (Me3S&N 200.4 4850 d. e Further evidence for the stereochemical identity of 200. l c the natural and synthetic crustecdysones is available Me,SiNHCOMe
