Zirconium-Promoted Ring Opening. Scope and Limitations

Hydrozirconation by means of [Cp2ZrHCl] n (2) of phospholene PhPCH2CHCHCH2 (1) leads to the β-zirconated phospholane 3 which reacts with phosphenium salts R2P+OSO2CF3 - (4, R = N i Pr2; 5, R = NCy2) to give unsaturated acyclic 1,1-diphosphines 6 or 7. Compound 3 also reacts with other electrophiles like [CH2NMe2]Cl, t BuCOCl, or HOSO2CF3 leading to unsaturated phosphines PhP(R)(CH2)2CHCH2, 8 (R = CH2NMe2), 9 (R = C(O) t Bu), or 10 (R = H), respectively. Hydrozirconation of 2,5-dihydrofuran (12) or 2,3-dihydrofuran (13) affords the acyclic zirconated species Cp2Zr(Cl)O(CH2)2CHCH2 (15), which reacts with 4, Ph2PCl, [CH2NMe2]Cl, PhCOCl, or HOSO2CF3 to give, via exchange reactions, the corresponding substituted olefines 16−20. Treatment of 12 or 13 with 2 equiv of 2 leads to dizirconated compound Cp2Zr(Cl)O(CH2)4Zr(Cl)Cp2 (21) which reacts with Ph2PCl (2 equiv) to give the phosphino−phosphinite Ph2PO(CH2)4PPh2 (22) isolated as its disulfide 23. 2-Methyl-4,5-dihydrofuran (24) treated first with 2 equiv of 2 and then with 2 equiv of Ph2PCl affords the phosphino−phosphinite Ph2PO(CH2)5PPh2 (26). Hydrozirconation of 2,5-dimethoxy-2,5-dihydrofuran (28) with 2 equiv of 2 gives rise to Cp2Zr(OMe)Cl (31) and Cp2Zr(Cl)O(CH2)2CHCHOMe (33), which react further with Ph2PCl (2 equiv) leading to phosphinites Ph2POMe (34) and Ph2PO(CH2)2CHCHOMe (35). Addition of 2 to 1-benzyl-3-pyrroline (36) allows the formation of the β-zirconated nitrogen five-membered ring PhCH2N(CH2)2CH(ZrCp2Cl)CH2 (37). 37 reacts with Ph2PCl giving rise to the acyclic aminophosphine Ph2PN(CH2Ph)(CH2)2CHCH2 (38) and to a substitute pyrroline 39. Derivative 37 also reacts with 4 to give the saturated nitrogen heterocycle 42, while it reacts with PhCOCl or HOSO2CF3 to afford the corresponding linear species PhC(O)N(CH2Ph)(CH2)2CHCH2 (44) or the amine HN(CH2Ph)(CH2)2CHCH2 (45). Hydrozirconation of 38 followed by addition of Ph2PCl and then addition of S8 gives the aminophosphine−phosphine disulfide Ph2P(S)N(CH2Ph)(CH2)4P(S)Ph2 (46). Hydrozirconation of oxygen six-membered rings such as 3,4-dihydro-2H-pyran (53) and 2-methoxy-3,4-dihydro-2H-pyran (55) is discussed as well as the hydrozirconation of a seven-membered ring, cis-dihydro-1,3-dioxepin (62). The behavior of 3-sila- (47) or 3-boracyclopentene (48) is also presented.