Regioselectivity in the formation of norbornene-fused pyrazoles: preparation of 1-substituted derivatives of 4,5,6,7-tetrahydro-1H-4,7-methanoindazole
作者:Franco Fernández、Olga Caamaño、Marcos Daniel García、Ibon Alkorta、José Elguero
DOI:10.1016/j.tet.2006.01.059
日期:2006.4
(±)-(exo,exo)-3-(hydroxymethylene)-5,6-(isopropylidenedioxy)bicyclo[2.2.1]heptan-2-one make the reactions between this β-diketone and hydrazines particularly interesting for elucidating the mechanism of pyrazole formation. The isolation and X-ray structure determination of two 5-hydroxy substituted Δ2-pyrazolines [(±)-(3aR*,4R*,5R*,6S*,7R*,7aR*)-7a-hydroxy-5,6-(isopropylidenedioxy)-3a,4,5,6,7,7a-hexahydro-4
(±)-(exo,exo)-3-(羟基亚甲基)-5,6-(异丙基二烯二氧基)双环[2.2.1]庚-2--2-的结构特征使该β-二酮与肼之间的反应特别有趣阐明吡唑的形成机理。分离和X射线结构测定的两个5羟基取代的Δ 2 -pyrazolines [(±) - (3A - [R *,4 - [R *,5 - [R *,6小号*,7 - [R *,7α - [R *) -图7a -羟基-5,6-(异丙基二烯二氧基)-3a,4,5,6,7,7a-六氢-4,7-甲醇-1 H-吲唑]和[(±)-(3a S *,4 R * ,5 R *,6 S*,7 R *,7a R *)-7a-羟基-5,6-(异亚丙基-二氧基)-1-苯基-3a,4,5,6,7,7a-六氢-4,7-甲基-1 H-吲唑]是确定机制的决定因素。除B3LYP / 6-31G *以外,还对所有中间体二羟基吡唑烷和5-羟基吡唑啉进行了计算。最后,已通过实验(13