2-Methyl-177-1,3-benzazaphosphole

Miles, J.A., Grabiak, R.C., and Beeny, M.T., Synthesis of novel phosphorus heterocycles 2-aryl-l-methyl-2,3-dihydro-lH-2,l-benzazaphosphole 1-ox-ides,. Org. Chem., 46, 3486, 1981. 

The crystal structure of 2-lithiated l-methyl-l,3-benzazaphosphole 35 showed it to have a dimeric structure with two THF molecules associated with each lithium. The two lithium atoms and the two C-2 atoms form a four-membered ring <20020M912>. In contrast, the N-lithiated derivative of 2,5-dimethyl-l//-l,3-benzazaphosphole exists as a monomeric species 36 in the solid state <2002JOM(646)113>. The carbene-type complex 37 derived from the lithiated species 35 on reaction with tungsten hexacarbonyl was also studied by X-ray crystallography. 

A four-membered ring was also found in the complex 38 formed by the reaction of 2-/i r/-butyl-5-methyl-l//-l,3-benzazaphosphole with nickelocine <2002ZFA2869>. 

A-Unsubstituted 1,3-benzazaphospholes and 1-methyl 1,3-benzazaphospholes are not basic and are not extracted from an organic phase by dilute sulfuric acid. They do not react with methyl iodide but are F/ -alkylated by Me30 BF4 <83JOM(258)257, 94MI 3i6-oi>. A P-Cr CO)i complex of 2-phenyl 1,3-benzazaphosphole is known <81ZAAC(481)22>. 

Like 1-methyl-1,3-benzazaphospholes/arsoles, the 1,3-benzoxaphospholes/arsoles (38) are unre-active to water, alcohols or amines. However, in contrast to them they add HCl, PhSH, and PhAsH2, and in the presence of AIBN they also add McjSnH. In this reaction (38a) is always less reactive than (38b) PhMePH only adds to (38b). Adducts (40) undergo a dismutation to yield the dihydro derivatives (41). (41) also results from (38a) and McsSnH. 

The reagent (60) generated in situ from the action of LiBu on phenyl isonitrile and r-butyl dichlorophosphine or methyl dichloroarsine gives the 3/7-1,3-benzazaphosphole/arsole (61) which is converted to the 1/7-1,3-benzazaphosphole/arsole (62) by flash vacuum pyrolysis (Scheme 6)... 

A variety of 2-functionalized 1,3-benzazaphospholes have been obtained by lithiation of l-methyl-l,3-benzazaphosphole with Bul.i in THF or Et20 followed by reaction with a suitable electrophilic reagent [72, 73], 1,3-Benzazaphospholes having bulkier A-substituents show tendency of addition of BuLi at the P = C bond [43 15, 72], Lithiation of 65 (R = neopentyl) yields a mixture of both C-lithiated and addition products however, in the presence of KO Bu, equilibrium shifts towards C-lithiation (Scheme 23). 

No reaction occurs with methyl iodide however, on reacting with Me2S04, [1,4,2] diazaphospholo[4,5-a]pyridines [27] and 11,2,3 diazaphospholo[4,5-a -pyridincs [34] furnish a2-A-methylated salts. Similar behaviour is shown by thiazolol 3,2-<7 [l,4,2]diazaphospholes [28], However, 1,3-benzazaphospholes are alkylated at phosphorus. This allows the access to N,P-disubstituted benzazaphospholium salts, potential precursors to heterocyclic 1,3-aminophosphinocarbenes [47],... 

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