Dibenzo phospholes

Some data are also available on the effect of the structure of the phosphine or diphosphine on the optical yield in the asymmetric hydrocarbalkoxylation of 2-phenyl-1-propene (24) (see Table III). The best optical yield was obtained using 2,2-dimethyl-4,5-bis(dibenzo-phosphol-5-ylmethyl)-l,3-dioxolane as the chiral ligand. Much lower optical yields were obtained using aminophosphines or monophosphines. 

R,R)2,2-Dimethyl-4,5-bis(5H-dibenzo- phosphol-5-ylmethyl)-l,3-dioxolane f-BuOH 240 0.8 not given (S) 69.0 24... 

Although no explanation was given for the spontaneous, unexpected oxidation steps 79- 78a and 78a- 34, it is reasonable to assume that the initially present tri-valent phosphorus compounds (phosphorus trichloride and 5-chloro-5H-dibenzo-phosphole 85, respectively), and/or the alkyl halide stemming from the halogen metal exchange reaction used for preparing 2,2 -dilithiobiphenyl, may play an active role here. 

The double oxidative intramolecular cyclization of bis(phenylphos-phinyl)-p-terphenyl afforded the diastereomers of twin bis(dibenzo-phosphole oxides) that were converted to the bis(sulfide derivatives) (Scheme 23). °... 

The phosphole ring can be fused to a number of other cyclic structures. The most widely found are the dibenzo- and dithieno-derivatives 9 and 10. It is noteworthy that these compounds display few properties associated with phospholes. Instead, they behave as diarylphosphines due to the presence of the highly aromatic fused benzene or thiophene rings. 

Many fused phospholes are known. Two examples are shown in equations (60) and (61) (67JA5732, 53LA(580)44). The first phosphole derivative (96) was prepared by Wittig, his method permitting the synthesis of many dibenzo [b, d]phospholes. Wittig also showed that when phenyldibenzophosphole was treated with phenyl azide the 1,1.1-triphenyIdiben-zophosphole (97) was formed via the 1-phenylphosphole-Af-phenylimine (equation (62)) (64CB741). 

The parent phosphole ring can be fused to a number of other cyclic structures for many of these compounds the coordination number can be varied, but most of the known compounds are found in phosphole form, or as the oxide derivative. The ring systems that are the most common are shown below. By far the most widely studied is the dibenzo derivative, because it is easily synthesized and worked with. However, the system displays few properties of a phosphole and is more like a diphenylphosphine. This system is accorded abbreviated attention for current interest, a series of papers by Cornforth et al. starting in 1982 should be consulted <82JCS(p1)2289>. 

Benzo[Z>]phosphole oxides (phosphindole oxides) and dibenzo[Z ,phosphole oxides are stable as the monomer, since Diels-Alder dimerization would require disruption of the aromatic ring system. The former are prepared by the dehydrohalogenation method (R = Ph <71CJC530> R = MeO <74AJC831, 82PS(13)259, 8INJC187 (Scheme 25). 

Phospholes are known to exhibit characteristic optical and electrochemical properties derived from the phosphorus-bridged 1,3-dienic jt system [34]. Particular interest has recently been paid to their Jt-conjugated derivatives, such as nonfused phospholes, dibenzo[f ,d] phospholes, benzo[f ] phospholes, benzo[c] phospholes, and related compounds [35]. There are several methods to synthesize phospholes [36]. The classical method for the synthesis of phospholes is the reaction between the nucleophilic substitution of a P-X bond with a stoichiometric amount of an organometallic species such as organolithium or organomagnesium reagents (Scheme 4.21) [37]. 

R, R, R , R = dibenzo overall yield from FcCHO= 31 % Scheme 5.3 Synthesis of the enantiomerically pure phosphole-alcohols 5 via Kagan s acetal... 

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