1,3‐Dioxanone Derivatives from β‐Hydroxy‐carboxylic Acids and Pivalaldehyde. Versatile Building Blocks for Syntheses of Enantiomerically Pure Compounds. A Chiral Acetoacetic Acid Derivative Preliminary Communication

( R )‐3‐Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis ‐ or ( R , R )‐2‐( tert ‐butyl)‐6‐methyl‐1,3‐dioxan‐4‐one ( 1a ), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively ( →3, 4, 5 , and 7 ). Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto‐acetic acid. Some reactions of 10 have been carried out, such as Michael addition (→ 11 ), alkylation on the CH 3 substituent (→ 13 ), hydrogenation of the CC bond (→ 1a ) and photochemical cycloaddition (→ 16 ). The overall reactions are substitutions on the one stereogenic center of the starting β‐hydroxy acid without racemization and without using a chiral auxiliary.