Synthetic Studies on Pandanus Alkaloids: From Norpandamarilactonines to Pandamarilactonines, a Proof of Their Configurational Instability

Abstract

The ethyl carbamate of norpandamarilactonine‐A was prepared in an enantiomerically pure form starting from (S)‐prolinol. Deprotection of the amine functionality rendered both diastereomeric norpandamarilactonines as racemates, which were used as synthetic precursors of pandamarilactonine‐A and ‐B. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The Vinylogous Aldol and Related Addition Reactions: Ten Years of Progress

“…[110][111][112][113] Here, the stereochemical outcome followed a similar trend, with syn-isomers preferentially formed in any case. With γ-substituted furan 256, reversal of stereochemistry was observed when fluoride ions were used as promoter (eq 4).…”

“…A convergent total synthesis of the antifungal agent khafrefungin (112) was devised by Kobayashi et al, 63 exploiting two highly diastereoselective homologative VMAR to implement the polypropionate seco-acid segment of the natural product. As illustrated in Scheme 19, the opening move was the VMAR between chiral/prochiral aldehyde 104 and L-valine-based Chemical Reviews REVIEW chiral/prochiral silyl N,O-acetal 94.…”

“…In a parallel fashion, VMAR homologation of propanal (107) with the enantiomer of 94 provided aldol 108, which was soon elaborated to complementary C1-C6 ketone fragment 109, ready for the final fragment assembly. Thus, aldol coupling between 106 and 109 proceeded uneventfully, giving rise to seco-acid 110, which was esterified with Lxylose-derived alcohol 111, providing khafrefungin (112) in synthetically useful yields (23% overall yield along 14 steps for the longest linear sequence from 107).…”

Synthesis of Norpandamarilactonines, Pandamarilactonines, and ­Pandanamine

“…[2][3][4][5][6] Until now, syntheses of norpandamarilactonines have been accomplished via the coupling reactions of suitably substituted pyrroles with the appropriate furan units or their precursors and also by employing a double ring-closing metathesis and further elaboration to the pandamarilactonines and pandanamine. [3][4][5][7][8][9][10] We felt that the aminobutenolide and iodobutenolide would be the appropriate precursors to design all these natural products in a concise fashion. These potential precursors amino-and iodobutenolides are readily available from commercially available 3-methylfuran-2(5H)-one via the corresponding common intermediate mesylbutenolide 11.…”

“…11 The diol 10 on treatment with phosphorus pentoxide in refluxing toluene gave a diastereomeric mixture of a-methyl-g-tetrahydrofuranylbutyrolactones 17 and 18 in ~1:1 ratio in 88% yield, which could be separated by column chromatography, via the intramolecular dehydrative cyclization pathway. 11 The diol 10 on treat-ment with methanesulfonyl chloride gave the desired mesylbutenolide 11 8 [E/Z = 57:43 ( 1 H NMR)] in 77% yield, following the double mesylation and an in situ monoelimination route. The mesylbutenolide 11 on chemoselective substitution reaction with sodium azide yielded, the azidobutenolide 12 [E/Z = 53:47 ( 1 H NMR)] in 87% yield.…”