Concerning the Stereochemical Course and Mechanism of the Photochemical 1,3-Acetyl Shift in a β,γ-Unsaturated Ketone. Preliminary Communication

Enantiomerically enriched samples of 1,2-dimethyl-3-(²H₃)methyl-2-cyclopentenyl (1) and 1-(²H₃)methyl-2,3-dimethyl-2-cyclopentenyl methyl ketones ( 2 ) have been irradiated at 313 nm in methanol in the temperature range +50 to ?45°. The 1,3-acetyl shift, which interconverts the two isomeric ketones, occurs with a small change in the enantiomeric composition and independently of temperature in the range studied. This change corresponds to an upper limit of approximately 20% reaction with racemization. It is proposed that reaction occurs from both the S₁(n, π*) and T₂(n, π*) excited states with stereospecific reaction from S₁ (rapid primary geminate recombination of a singlet radical pair, with a possible contribution by a concerted 1,3 shift) dominating throughout the temperature range, but with the proportion of reaction from T₂ increasing as the temperature is lowered. The racemization results from secondary geminate recombination of the singlet and triplet radical pairs and the random recombination of free radicals. Viscosity effects are proposed to explain the independence of the racemization on temperature.     

Direct Catalytic Asymmetric Doubly Vinylogous Michael Addition of α,β‐Unsaturated γ‐Butyrolactams to Dienones

An asymmetric doubly vinylogous Michael addition (DVMA) of α,β‐unsaturated γ‐butyrolactams to sterically congested β‐substituted cyclic dienones with high site‐, diastereo‐, and enantioselectivity has been achieved. An unprecedented DVMA/vinylogous Michael addition/isomerization cascade reaction affords chiral fused tricyclic γ‐lactams with four newly formed stereocenters.     

Crystallographic report: Dichloro(β‐methoxycarbonylethyl)tin(IV) isopropylxanthate

The Sn atom in CH₃OCOCH₂CH₂SnCl₂[S₂COCH(CH₃)₂] adopts a distorted octahedral geometry via the bidentate xanthate ligand and intramolecular carbonyl coordination. Copyright © 2005 John Wiley & Sons, Ltd.