Arsoles, synthesis

Thus the synthesis of diheteroferrocenes depends on the availability of the corresponding heteroles, which have been prepared by just a few routes. l-Phenyl-2,5-disubstituted arsoles are prepared generally from the corresponding 1,3-diynes by the base-catalyzed addition of phenylarsine. In this manner, Markl and Hauptmann have prepared 1-phenyl-2,5-dimeth-ylarsole (25) in 30% yield.4 Subsequently, Mathey et al. used this arsole to prepare the first diarsaferrocene 26.5 (see Scheme 2.)... 

There is a good synthesis of the C-unsubstituted 1-phenylarsole (34). The reaction of dilithiophenylarsine with the readily available mixture of isomeric 1,4-dichloro- 1,3-butadienes (33) gives 34 in 25% yield.13 The arsole 34 is easily converted to 1,1 -diarsaferrocene (8), while 1,1 -diphos-phaferrocene (7) can be prepared analogously, as shown in Scheme 4. The lack of availability and low stability of phenylstibine and phenylbismuthine limit extension to preparation of the heavier diheteroferrocenes. 

This synthesis of the 1,3-benzoxaphospholes (9) and 1,3-benzoxaarsoles (24) is analogous to that of 1,3-benzazaphospholes/arsoles (57) in Section 3.16.4.1.2, using 2-phosphino/arsinophenols to start with. 

Little has been published on the synthesis of fully saturated derivatives of arsoles, stiboles, or bismoles. There are now bismolane derivatives, and their syntheses will be covered in this section. The synthesis of bis(methylene)stibolanes and -bismolanes is covered in Sections 2.16.8.1.1.3(iv). Atkinson s review also covers general syntheses of arsolanes and stibolanes <84CHEC-I(1)539>. The preparation of anions of the tetrahydro derivatives is covered in Section 2.16.10.1. 

Anions of arsoles, stiboles, bismoles, stibolanes, and bismolanes are known. Although the highly colored species are reactive, they are stable when handled properly. Their lone-pair electrons are fully delocalized and thus are considered to be aromatic. They are used as intermediates in the synthesis of l,r-biheteroles, alkylated products, or organometallic derivatives, which may either be a- or 7t-bonded. 

Arsoles, stiboles, and bismoles act as soft ligands and have found considerable application in the synthesis of both a- and r-organometallic complexes. These compounds exhibit interesting conformational properties, by existing as eclipsed and staggered structures for which inversion... 

Owing to the lability of the tin-carbon bond, stannoles were the first heterocyciopentadienes to be transformed into other heteroles boroles , arsoles or stiboles ° and auroles. However, since their synthesis is presently less easy for the C-unsubstituted or alkyl substituted derivatives than in the case of the corresponding siloles or germoles, they are not useful reagents for preparing these heteroles. 

The complexes (CXVI) are analogous to the derivatives (CIV) discussed in Section V, B. The tetraphenyl derivative (CXVI. 1) gives the tetracyclone-Fe(CO)3 complex (CXIII.l) upon bromination and with methanolic NaOH yields tetraphenylbutadiene-Fe(CO)3 (38, 39, 128). Reaction of this tetraphenyl derivative with appropriate reagents has provided a novel synthesis of furans, thiophenes, selenophenes, pyrroles, phospholes, and arsoles (38, 78, 128). 

A number of synthetic methods have developed for construction of the heterole skeletons. The most straightforward and atom-economical method for the synthesis of 2,5-disubstituted heteroles is the double addition of X—H bonds across 1,3-diynes, albeit it requires trans addition to the carbon-carbon triple bonds. Thiophenes [2], selenophenes [3], teUurophenes [4], phospholes [5], arsoles [6], and stannoles [7] have been synthesized by using this method without the aid of catalysts ... 

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