2-biphenylyl-

Many carbamates have been used as protective groups. They are arranged in this chapter in order of increasing complexity of stmcture. The most useful compounds do not necessarily have the simplest stmctures, but are /-butyl (BOC), readily cleaved by acidic hydrolysis benzyl (Cbz or Z), cleaved by catalytic hy-drogenolysis 2,4-dichlorobenzyl, stable to the acid-catalyzed hydrolysis of benzyl and /-butyl carbamates 2-(biphenylyl)isopropyl, cleaved more easily than /-butyl carbamate by dilute acetic acid 9-fluorenylmethyl, cleaved by /3-elimination with base isonicotinyl, cleaved by reduction with zinc in acetic acid 1-adamantyl, readily cleaved by trifluoroacetic acid and ally], readily cleaved by Pd-catalyzed isomerisation. 

Biphenylyl diphenyl phosphate [132-29-6] M 302.4, n l.5925. Vacuum distd, then percolated through an alumina column. Passed through a packed column maintained at 150° to remove residual traces of volatile materials by a counter-current stream of nitrogen at reduced pressure. [Dobry and Keller J Phys Chem 61 1448 1957.]... 

Bis-(2-chlorophenyl) phenyl phosphate [597-80-8] M 395, b 254"/4mm, n 1.5767. Same as for 2-biphenylyl diphenyl phosphate above. 

Tris-(2-biphenylyl) phosphate [132-28-5] M 554.6, m 115.5-117.5". Crystd from MeOH containing a little acetone. 

Biphenylyl)urea, 31,10 l-(4-Biphenylyl)urea, 31, 10 Bis-4-chlorobutyl ether, 37, 55 Bischi-oromethyl ether, 36,1... 

Formation of 131 in a high yield (85%) on the photolysis of ethyl 2-biphenylyl carbamate (134) is not surprising on the basis of the discussion for the conversion 110 -> 112. Other carbamates 27,7,11 rearranging via sterically strained 4- and 6-ring transient states, afford normal rearranged products 28-30. Here also, as was the case with the irradiation of aryl esters, higher yields of ortho and para products were obtained in polar solvents (ethanol, t-butanol) than in the nonpolar n-hexane.11... 

Bis-(/7-ieri-butylphenyl)phenyl phosphate [115-87-7] M 438.5, b 281"/5mm, n 1.5412. Same as for 2-biphenylyl diphenyl phosphate (above). 

X-ray and P NMR studies of (T -cyclohexenyl)palladium complex of 53 concluded that high enantioselectivity is due to the exclusive formation of an exo 7t-allylpalladium intermediate induced by the interaction between the 2-biphenylyl group and the Mn(CO)3 moiety. 

Cleavage of the C(4)-fluorene bond produces a 4-(2-biphenylyl)thiopyrylium radical 383 and initiates the polymerization process (Equation 91) <1996SM(83)153>. 

Phenanthridone has been obtained by the action of carbon dioxide on 2-lithioaminobiphenyl49 and by cyelizing 2-biphenylyl isocyanate with aluminum chloride,50 the latter reaction appearing to be a general one. Thus, cyclization of 5-bromo-2-biphenylyl isocyanate gives 2-bromophenanthridone,51 while reaction of the isocyanate (17) with trifluoroacetic acid is a key stage in the synthesis of dihydroxy-crinene (18).52... 

On the basis of these findings a new level had been reached, from which a very efficient pursuit of the stereochemical and other questions pertinent to those classes of compounds became possible. In this respect, the key reaction consisted in the protolytic cleavage of phosphate ion 57 to give 2-biphenylyl-bis-2,2 -biphenylylene-phosphorane 25 d. On the assumption that 57 very probably had an octahedral structure, it was then hoped that the fate of the optical activity on protolytic cleavage of optically active forms of this ion would also enable some conclusions on the stereochemistry of the resulting phosphorane 25 d to be made. The resolution of 57 could readily be achieved with methylbrucinium iodide and finally yielded the optically active potassium salts K-57 with = 1930 and [M] = 10164° 66). 

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