Diastereoselective Michael addition of (S)-mandelic acid enolate to 2-arylidene-1,3-diketones: enantioselective diversity-oriented synthesis of densely substituted pyrazoles
作者:Gonzalo Blay、Isabel Fernández、Eva Molina、M. Carmen Muñoz、José R. Pedro、Carlos Vila
DOI:10.1016/j.tet.2006.06.009
日期:2006.8
utilises the conjugated addition of the lithium enolate of the (2S,5S)-cis-1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde to several 2-arylidene-1,3-diketones, which proceeds readily to give the corresponding Michael adducts in good yields and diastereoselectivities. The cyclocondensation of the 1,3-diketone moieties present in Michael adducts with several hydrazines
对映体纯稠密取代的吡唑,α-芳基-α-吡唑基对羟基苯甲酸和α-芳基-α-吡唑基苯乙酮的多样性导向方法已得到开发。该方法利用共轭加成的旋光性(S S,5 S)-顺式-1,3-二氧戊环4-1的烯醇锂)-扁桃酸和新戊醛成几个2-芳基-1,3-二酮,容易进行制得具有良好收率和非对映选择性的相应的迈克尔加合物。存在于迈克尔加合物中的1,3-二酮部分与几种肼的环缩合导致对映体纯的稠密取代的吡唑。这些产物中存在的二氧戊环酮部分随后的碱性水解产生对映体纯的α-芳基-α-吡唑基聚乳酸。最后,使用氧气,新戊醛和Co(III)-Me 2 opba络合物作为催化剂将它们氧化脱羧,得到α-芳基-α-吡唑基乙酰苯。在这种方法中,引入了四个分集点,其中之一是(S)-扁桃酸,它是苯甲酰基阴离子的手性手性当量。