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A Butyrolactone → 1,3‐Diol Strategy for the Obtention of Tolypothrix Polyethers – Stereoselective Synthesis of a Key Lactone Precursor
Author(s) -
Priepke Henning,
Weigand Stefan,
Brückner Reinhard
Publication year - 1997
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719970804
Subject(s) - chemistry , ozonolysis , lactone , enantioselective synthesis , diol , orthoester , context (archaeology) , stereoselectivity , double bond , oxazoline , stereochemistry , organic chemistry , catalysis , paleontology , biology
A novel access to 1,3,5,7,…‐polyols is developed. It follows – in the context of the planned synthesis of the natural permethylated 1,3,5,7,9‐pentaol 1a from the blue‐green alga Tolypothrix conglutinata – the strategy depicted in Scheme 4. The present paper concerns the enantioselective synthesis of the key building block syn ‐ 9a . This γ‐lactone was derived from O‐tert ‐butyldiphenylsilylglycidol ( R − 15 ) via a synthetic equivalent of the 6‐hydroxy‐4‐ketoester 12 (cf. Scheme 5). As such, we used the hydroxydiene 28 rather than the 2‐(5‐hydroxy‐3‐methylenepentyl)‐1,3‐oxazoline 26 or the (5‐hydroxy‐3‐methylenepentyl)‐substituted orthoester 27 because of its greater ease of preparation (cf. Scheme 7). A double ozonolysis of the hydroxydiene 28 provided the desired 6‐hydroxy‐4‐ketoester 12 itself (Scheme 8). The CO bond of this compound was reduced syn ‐selectively ( ds = 100:0) through successive additions of Et 2 B(OMe) and NaBH 4 and anti ‐selectively ( ds = 80:20) through the addition of NaBH(OAc) 3 (Scheme 9). The dihydroxy ester syn ‐ 34 formed in the mentioned syn ‐selective reduction was isolable or could be lactonized in the presence of acid so that the syn ‐configured hydroxy lactone syn ‐ 9a was obtained directly (Scheme 10).