Chirale Synthesebausteine durch Kolbe ‐Elektrolyse enantiomerenreiner β‐Hydroxy‐carbonsäurederivate. ( R )‐ und ( S )‐Methyl‐sowie ( R )‐Trifluormethyl‐γ‐butyrolactone und ‐δ‐valerolactone

Chiral Building Blocks for Syntheses by Kolbe Electrolysis of Enantiomerically Pure β‐Hydroxybutyric‐Acid Derivatives. ( R )‐ and ( S )‐Methyl‐, and ( R )‐Trifluoromethyl‐γ‐butyrolactones, and ‐δ‐valerolactones The coupling of chiral, non‐racemic R* groups by Kolbe electrolysis of carboxylic acids R*COOH is used to prepare compounds with a 1.4‐ and 1.5‐distance of the functional groups. The suitably protected β‐hydroxycarboxylic acids ( R )‐ or ( S )‐3‐hydroxybutyric acid, ( R )‐4,4,4‐trifluoro‐3‐hydroxybutyric acid (as acetates; see 1 – 6 ), and ( S )‐malic acid (as (2 S ,5 S )‐2‐( tert ‐butyl)‐5‐oxo‐1,3‐dioxolan‐4‐acetic acid; see 7 ) are decarboxylatively dimerized or ‘codimerized’ with 2‐methylpropanoic acid, with 4‐(formylamino)butyric acid, and with monomethyl malonate and succinate. The products formed are derivatives of ( R , R )‐1,1,1,6,6,6‐hexafluoro‐2,5‐hexanediol (see 8 ), of ( R )‐5,5,5‐trifluoro‐4‐hydroxypentanoic acid (see 9,10 ), of ( R )‐ and ( S )‐5‐hydroxyhexanoic acid (see 11 ) and its trifluoro analogue (see 12, 13 ), of ( S )‐2‐hydroxy‐ and ( S , S )‐2,5‐dihydroxyadipic acid (see 23, 20 ), of ( S )‐2‐hydroxy‐4‐methylpentanoic acid (‘OH‐leucine’, see 21 ), and of ( S )‐2‐hydroxy‐6‐aminohexanoic acid (‘OH‐lysine’, see 22 ). Some of these products are further converted to CH 3 ‐ or CF 3 ‐substituted γ‐ and δ‐lactones of ( R )‐ or ( S )‐configuration ( 14 , 16 – 19 ), or to an enantiomerically pure derivative of ( R )‐1‐hydroxy‐2‐oxocyclopentane‐1‐carboxylic acid (see 24 ). Possible uses of these new chiral building blocks for the synthesis of natural products and their CF 3 analogues (brefeldin, sulcatol, zearalenone) are discussed. The olfactory properties of ( R )‐ and ( S )‐δ‐caprolactone ( 18 ) are compared with those of ( R )‐6,6,6‐trifluoro‐δ‐caprolactone ( 19 ).