Abstract
Expedient asymmetric total syntheses of both (R)-podoblastin-S and (R)-lachnelluloic acid, representative of natural 3-acyl-5,6-dihydro-2H-pyran-2-ones, were performed. Compared with the reported total synthesis of (R)-podoblastin-S (14 steps, overall 5% yield), the present study was achieved in only five steps in an overall 40% yield and with 98% ee (HPLC analysis). In a similar strategy, the first asymmetric total synthesis of the relevant (R)-lachnelluloic acid was achieved in an overall 40% yield with 98% ee (HPLC analysis). The crucial step utilized readily accessible and reliable Soriente and Scettri’s Ti(OiPr)4/(S)-BINOL‒catalyzed asymmetric Mukaiyama aldol addition of 1,3-bis(trimethylsiloxy)diene, derived from ethyl acetoacetate with n-butanal for (R)-podoblastin-S and n-pentanal for (R)-lachnelluloic acid. With the comparison of the specific rotation values between the natural product and the synthetic specimen, the hitherto unknown absolute configuration at the C(6) position of (−)-lachnelluloic acid was unambiguously elucidated as 6R.
Highlights
Expedient asymmetric total syntheses of both (R)-podoblastin-S and (R)-lachnelluloic acid, representative of natural 3-acyl-5,6-dihydro-2H-pyran-2-ones, were performed
3-Acyl-5,6-dihydro-2H-pyran-2-one is a unique heterocyclic molecule with a tricarbonyl moiety on the C(3)-carbon, which is found in natural products [1]
Alternaric acid (1) is the most representative phytotoxic and antifungal compound isolated from Alternaria solani [2]
Summary
Expedient asymmetric total syntheses of both (R)-podoblastin-S and (R)-lachnelluloic acid, representative of natural 3-acyl-5,6-dihydro-2H-pyran-2-ones, were performed. The first asymmetric total synthesis of the relevant (R)-lachnelluloic acid was achieved in an overall 40% yield with 98% ee (HPLC analysis). The crucial step utilized readily accessible and reliable Soriente and Scettri’s Ti(OiPr)4 /(S)-BINOL-catalyzed asymmetric Mukaiyama aldol addition of 1,3-bis(trimethylsiloxy)diene, derived from ethyl acetoacetate with n-butanal for (R)-podoblastin-S and n-pentanal for (R)-lachnelluloic acid. 3-Acyl-5,6-dihydro-2H-pyran-2-one is a unique heterocyclic molecule with a tricarbonyl moiety on the C(3)-carbon, which is found in natural products [1]. Very recently, we performed relevant asymmetric total synthesis of azaspirene, a unique hetero-spirocylic γ-lactam-type antibiotic, utilizing. The obtained unambiguously clarified that the naturally occurring specimens were made upmade of mixtures of A, B, outcome unambiguously clarified that the naturally occurring specimens were up of mixtures and
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