Ylides of Selenium and Tellurium

Freeman and Lloyd applied their now standard method to prepare diphenyltelluronium-2,3,4,5-tetraphenylcyclopentadienide (129). This first tellurium ylide was very weakly basic and would not undergo the typical ylide reactions with / -nitrobenzaldehyde or nitrosobenzene. 

By application of the Horner method, developed originally for the preparation of stabilized phosphonium ylides, Emstbrunner and Lloyd  

30S Yamada, T. Nishiyama, M. Kinugasa, and M. Nakatani, Bull. Chem. Soc. Japan, 1970, 43, 3611. 

Less work has been reported in this area during the past two years. The majority of papers have been concerned with thiabenzenes and nitrogen-containing derivatives. 6a-Thiathiophthens and related compounds are accorded separate treatment (Chapter 8) in view of the volume of published work on this subject. 

Further attempts have been made to prepare stable 1-substituted 2,4,6-triarylthiabenzenes. Previously it had been shown that 1,2,4,6-tetra-phenylthiabenzene (1) is unstable to heat, light, and oxygen, this instability being attributed to steric effects arising from overcrowding of substituents at positions 2, 1, and 6 (see ref. 2). In order to alleviate the 

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