Reaktionen mit Phosphinalkylenen, XII. Eine neue Synthese von Allen‐carbonsäureestern

Abstract

Bei der Umsetzung von SBurechloriden RRCH-COCl mit zwei Molekulen eines stabilen Ylids R'-CCC02C2H5 entstehen Allencarbonsaure-athylester. Die Reaktion verliiuft uber I 1 P(CSHd3 eine y-Eliminierung an einem intermediir gebildeten Phosphoniumsalz.Triphenylphosphinalkylene (l), die an der C=P-Doppelbindung ein H-Atom tragen, reagieren mit verschiedenen organischen Halogenverbindungen 2 unter primlrer Bildung eines Phosphoniumsalzes 3, das dann, wenn R elektronenanziehend ist, sofort mit einem zweiten Molekiil des Ylids 1 unter Umylidierung4) zum neuen Phosphinalkylen 4 und dem Phosphoniumsalz 5 reagierts). Mit Hilfe dieser Reaktion lassen sich Phosphinalkylene acylieren6). alkoxycarbonylieren7) und alkylieren 8).

Two-fold tandem acyl-group shift/cyclization via gold catalysis

“…Installation of the allene moiety was performed by reaction of ylide 3 with ketene, generated in situ from acyl chloride and triethylamine. [22][23][24][25][26][27] Allenoyl derivative 4 could thus be obtained in 80% yield from α-bromoester 3. Final desilylation by means of potassium fluoride delivered 5 possessing the desired terminal triple bond in 63% yield.…”

Total Synthesis of Thuggacin B

“…The formation of the synaldol product was confirmed after preparation of the 1,3-syndiol using NaBH 4 in the presence of Et 2 BOMe [23] and formation of the acetonide. The acetonide showed the expected coupling constants (J) and 13 C NMR chemical shifts [24] of the acetonide carbon atoms (Scheme 5). After saponification and oxidation alkyne 5 was generated by action of Bestmanns reagent.…”

“…Extending the reaction time without removing the freshly formed thuggacin B led to decomposition (presumably elimination of water at C7/C8 as well as methanolysis). The spectroscopic data ( 1 H NMR, 13 C NMR, HRMS, CD) of the synthetic thuggacin B (2) are identical to those of an authentic sample of 2. Moreover, we observed slow rearrangement of thuggacin B into the thuggacins A (1) and C (3) in the NMR tube.…”

“…Olefination with ylide 14 [13] had to be optimized with respect to the desired E selectivity and complete conversion of aldehyde 13. We found that a high excess of ylide 14 and low concentration of aldehyde are required to prevent decomposition of aldehyde 13.…”

Chiral separation of 2,3‐allenoic acid by capillary zone electrophoresis using cyclodextrin derivatives

“…12,20,21 The molecular structures are shown in Figure 1. The sample solutions were all made as water solutions with the aid of a little NaOH solution (0.1 mol/L).…”