Orthocarbonsäure‐ester mit 2,4,10‐Trioxaadamantanstruktur als Carboxylschutzgruppe; Verwendung zur Synthese von substituierten Carbonsäuren mit Hilfe von Grignard‐Reagenzien

Ortho Esters with 2,4,10‐Trioxaadamantane Structure as Carboxyl Protecting Group; Applications in the Synthesis of Substituted Carboxylic Acids by Means of Grignard Reagents The surprising stability of 2,4,10‐trioxa‐3‐adamantyl derivatives 1 against nucleophilic substitution by organomagnesium compounds is discussed and shown to be caused by unfavourable stereoelectronic and steric factors governing the substitution of these cage compounds (Scheme 2). As a consequence, a number of Grignard reagents 2 containing the carboxyl group masked as 2,4,10‐trioxa‐3‐adamantyl group could be prepared and have been reacted in a second step with various electrophiles (cf. Scheme 4). In the products 7–13 and 15b the carboxyl masking group is removed by mild acid hydrolysis and saponification (cf. Scheme 3) to yield the corresponding acids 16a–21a, 22, and 23a. Acids 21a and 23a have been further transformed to give the macrocyclic lactones 24 and 26, isolated from Galbanum oleo‐gum‐resin, and acid 22 to give 12‐methyl‐13‐tridecanolide (25), isolated from Angelica root oil. In addition 1‐bromo‐ω‐(2,4, 10‐trioxa‐3‐adamantyl)alkanes 1c and 1b have been used to synthesize (±)‐methyl recifeiolate (29b) and pure cis‐ambrettolic acid ((Z)‐32a).