1.4- Dihalides benzene ring

In the second reaction, the dihalide (methylene chloride) may react with 2 benzene rings to yield a diphenyl compound. Since benzene is in excess this reaction will take place. The second reaction is presented in figure B and the product is diphenylmethane. 

It is facile to prepare dibenzyl derivatives, such as 78, when the corresponding Grignard reagents are stable. However, when they are not, because of the occurrence of an intensive polycondensation of the dihalide in spite of high dilution conditions, Barbier conditions prove to be very efficient (Scheme 3.7.12). The simultaneous reaction of l,4-bis(chloromethyl)benzene or 4,4 -bis(chloromethyl)biphenyl with tricyclohexyltin chloride and magnesium allows the preparation of -substituted dibenzyl derivatives 81 and 84, with one or two phenyl rings. 

G. RING CLOSURE TO FORM A DIBENZOAZA-CROWN CONTAINING ANY COMBINATION OF FOUR PHENOLIC O—C AND ANILINIC N—C BONDS BY A 2 2 CYCLIZATION OF o-DISUBSTITUTED (HYDROXY AND/OR AMINO) BENZENE WITH A DIHALIDE OR DITOSYLATE ESTER... 

By analogy with pyrrole and phosphole chemistry, carbenes, which are generated from the dihalide and base or from PhHgCCl2Br (R = Bu ), add to the arsole ring to give bicyclo[3,1.0] derivatives (Equation (10)), of which certain ones (R = Bn, Bu ) serve as precursors of the arsa-benzenes (49) and (74) <74TL203>. 

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