Bernd Nestler

Dimethyldioxirane epoxidation of α,β-unsaturated ketones, acids and esters.

Abstract The corresponding epoxides were isolated in excellent yields via oxygen transfer by dimethyldioxirane ( as acetone solution).

(Z)-3-Methyl-3-penten-2-ol as stereochemical probe for 1,2 versus 1,3 allylic strain in the photooxygenation and epoxidation of chiral allylic alcohols

Abstract The importance of 1,2 versus 1,3 allylic strain in hydroxy-directed reactions can be assessed from reactions of (Z)-3-methyl-3-penten-2-ol, which is demonstrated for the ene reaction of singlet oxygen and the epoxidations by m -CPBA and VO(acac) 2 /t -BuOOH; furthermore these results provide insight into transition state geometries for such hydroxy-directed oxygen transfer reactions.

Photooxygenation of 2-alkenyl substituted chiral oxazolines : Stereochemical evidence favouring the cis effect in the regioselective ene reaction of singlet oxygen with α,β-unsaturated carbonyl derivatives

Abstract Photooxygenation of the title compound afforded hydroperoxides through regioselective ene reaction of singlet oxygen at the allylic position proximate to the heterocycle; the lack of diastereoselectivity in these ene reactions is taken as evidence against initial [4+2] cycloaddition of the enophile with the heterodiene.

HYDROXY-DIRECTED DIASTEREOSELECTIVE ENE REACTION OF TRIAZOLINEDIONES WITH CHIRAL ALLYLIC ALCOHOLS

Abstract The ene reaction of the N -methyltriazolidinone (MTAD) with the allylic alcohols 1a-e afforded the corresponding urazoles 2 in high threo diastereoselectivity (Scheme 1). These results are mechanistically explained in terms of an attractive hydrogen-bonding interaction between the enophile and the allylic hydroxy functionality in the threo transition state, which is favored on account of minimal 1,3-allylic strain. The threo diastereoselectivity is completely lost when the allylic hydroxy-functionality is masked. The results parallel the hydroxy-directing effect previously established in the singlet-oxygen ene reaction.