Aldol Additions of Titanium and Boron Enolates of Achiral and Chiral -Lactones to Achiral Model Aldehydes: Simple and Induced Diastereoselectivities

作者：Weber Fabian; Becker Fabian; Keller Manfred; Hillebrecht Harald; Brueckner Reinhard

来源：European Journal of Organic Chemistry, 2015, 2015(36): 7892-7918.

DOI：10.1002/ejoc.201501128

• Aldol reactions
• -Hydroxy esters
• -Lactones
• Boron enolates
• Titanium enolates
• Diastereoselectivity
• Configuration determination

We studied the steric course of aldol additions of CpTiCl2 (novel) or Bu2B enolates of the unsubstituted -lactone and of the four monomethylated -lactones to isobutyraldehyde, crotonaldehyde, and para-bromobenzaldehyde. The titanium enolates reacted syn-selectively with >95:5 ds in most cases. The boron enolates reacted anti-selectively without exception (ds = 98:2 to 92:8). These selectivities paired with a preferred trans-orientation of the -hydroxyalkyl substituents relative to the lactone's - or -methyl group and with a preferred cis-orientation relative to the lactone's -methyl group. Our preparation of -methyl--lactone (20) features a tandem glycol cleavage/lactollactone conversion with cat. TEMPO/stoichiom. PhI(OAc)(2), which we believe is novel.

• 出版日期2015-12