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Journal ArticleDOI

A new route to o-allenylphenols

01 Jan 1994-Journal of The Chemical Society, Chemical Communications (The Royal Society of Chemistry)-Iss: 10, pp 1177-1177

AbstractCathodic reduction of 3-bromochromenes led to a ring-opening reaction yielding o-allenylphenyl acetates.

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Citations
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Book ChapterDOI
01 Jan 1996

43 citations

Journal ArticleDOI
TL;DR: A general and efficient synthesis of allenes using a palladium(0)/diethylzinc system is described, with good to high yields of mesylates or trichloroacetates of (E)- or (Z)-2-bromoalk-2-en-1-ols.
Abstract: A general and efficient synthesis of allenes using a palladium(0)/diethylzinc system is described. Treatment of mesylates or trichloroacetates of (E)- or (Z)-2-bromoalk-2-en-1-ols with diethylzinc in the presence of a catalytic amount of palladium(0) affords allenes bearing an aminoalkyl, alkyl, or aryl substituent(s) in good to high yields. No transfer of chirality from the stereogenic center carrying the mesyloxy group to the allene was observed.

35 citations

Journal ArticleDOI
Abstract: Hydrosilylation of ynals with triethylsilane is catalyzed by RhCl(PPh3)3 and leads to α-triethylsilyl enals. Addition of aryl Grignard reagents takes place to give secondary allylic alcohols which are easily converted to 1,3-disubstituted allenes.

23 citations

Book ChapterDOI
TL;DR: Developments in marine ladder polyethers that include synthetic studies on brevetoxin, ciguatoxinm, gambierol, gymnocin-A, and yessotoxin are discussed and their transformation into a range of useful products are discussed.
Abstract: Publisher Summary This chapter provides information on six-membered ring systems with O and/or S atoms. The chapter discusses heterocycles containing one oxygen atom, including pyrans, benzopyrans (chromenes), dihydrobenzopyrans (chromans), pyranones, coumarins, chromones, flavonoids, xanthones, and pyrylium salts. The chapter discusses heterocycles containing one sulfur atom, including thiopyrans and analogues. The chapter also discusses heterocycles containing two or more oxygen atoms, including dioxins, and trioxins. The chapter also discusses heterocycles containing two or more sulfur atoms, including dithianes, and trithianes. Oxathiines are discussed under heterocycles containing both oxygen and sulfur in the same ring. The hetero-Diels-Alder (HDA) reaction involving aldehydes is catalyzed by Pd(II) complexes, such that even non-activated dienes give satisfactory yields of 5,6-dihydro-2Hpyrans. Chiral aluminium complexes are effective in controlling both the chemo- and enantio- selectivity of the reaction of alkyl glyoxylates with dienes containing an allylic C-H bond; high yields of the dihydropyran result with enantiomeric excesses of up to 97%. Stannyl derivatives of 2H-pyran-2-one, accessible from bromopyranones by cross coupling with organotin reagents, themselves take part in Pd(0)-catalyzed cross coupling with enol triflates. This methodology offers a new approach to steroidal pyran-2-ones.

11 citations

Journal ArticleDOI
Abstract: The intramolecular transfer of allyl moieties from substituted allyl aryl ethers to carbonyl groups has been studied by electrosynthesis, in a nickel-catalysed reaction The influence of metal ions such as Mg 2+ , Zn 2+ and Al 3+ has been examined Regioselectivity towards the branched isomer was better with Zn 2+ than with Mg 2+ ions, but it was higher in the absence of added metal ions

4 citations


References
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Journal ArticleDOI
Abstract: It is known that propargyl-phenylethers rearrange at about 200° to 2 H-chromenes [1–4]. It is shown that this rearrangement occurs in benzene or chloroform at lower temperatures (20–80°) in the presence of silver-tetrafluoroborate (or-trifluoracetate). The ethers examined are presented in Scheme 1. Thus in chloroform at 61° in the presence of AgBF4, phenyl-propargylether (3) yields 2 H-chromene (13). With 0.78 molar equivalents AgBF4 in benzene at 80° the same ether 3 yields a 3:1 mixture of 2-methyl-cumaron (14) and 2 H-chromene (13). From 1′-methylpropargyl-phenylether (4) and 2′-butinyl-3,5-dimethylphenylether (5) under similar conditions the corresponding chromenes 16 and 17 resp. are obtained. Rearrangement of propargyl- and 2′-butinyl-1-methyl-2-naphthylether (6 and 7 resp.) in benzene at 80° in the presence of AgBF4 gives the corresponding allenyl-naphthalenones 18 and 19 resp. Treatment of propargyl- and 2′-butinyl-mesityl-ether (8 and 9 resp.), and propargyl- and l′-methylpropargyl-2,6-dimethyl-phenylether (10 and 11 resp.) in benzene at 80° with AgRF, yields as the only product the corresponding 3-allenyl-phenols 21, 22,24 and 25 (Scheme 3). It is shown that in the presence of μ-dichlor-dirhodiuni (1)-tetracarbonyl in benzene a t 80° the ether 4 rearranges to 2-methyl-2H-chromene (16). However with this catalyst the predominant reaction is a cleavage to phenol. No reaction was observed when ethers 3 and 12, (Scheme 7 ) were treated with the tris-(trimethylsily1)-ester of vanadic acid in benzene a t 80° (see also [8]). By analogy with the known mechanism for thc silver catalysis of the reversible propargylesterl/allenylester rearrangement [S], the silver (1)ion is assumed to form a pre-equilibrium π-complex with the C, C-triplebond of the substrate. This complex then undergoes a [3s, 3s]-sigmatropic rearrangement (Scheme 2). In the case of the others 6, 7 and 12 the resulting allenyldienones were isolated. The 2,G-dimethyl substituted ethers 8, 9, 10 and 11 resp. first give the usual allenyl- dienones (Scheme 3). These then undergo a novel silver catalysed dienon-phenol-rearrangement (Sclzenzu4) to give the 3-allenylphenols 21, 22, 24 and 25. Thc others 3, 4 and 5 with free ortho positions presumably rearrange first to the non-isolated 2-allenyl-phenols 15, 42 and 43 resp.(Scheme 7). These then rearrange, either thermally or by silver (1)ion catalysis to the 2H-chromenes 13,16 and 17 resp. The rate of the rearrangement of 2-allenylphenol (15) to 13 at room temperature in benzene or chloroform is approximately doubled when silver ions are present as catalyst.

57 citations

Journal ArticleDOI
Abstract: The acid catalysed dienol-benzene rearrangement of methyl substituted o- and p-propargylcyclohexadienols (18–22, 34 and 35) was investigated. In the first step water is eliminated to yield the corresponding methyl propargyl benzonium ions (cf. scheme 6, a), which undergo [1s, 2s] sigmatropic rearrangements to give propargylbenzenes (28, 29, 30, 38) and [3s, 4s] sigmatropic rearrangements to give allenylbenzenes (24–27, 40) (cf. schemes 2, 3, 5, 6). [3s, 3s] sigmatropic rearrangements occur only to a small extend. In the rearrangement of 2-propargyl-2,4,6-trimethylcyclohexa-3,5-dien-1-ol (18) a [1s, 2s] sigmatropic methyl shift is observed (4%).

24 citations

Journal ArticleDOI
Abstract: The synthesis of the potent potassium channel opener Ro 31-6930 is reported. Methods of controlling the regiochemistry of the crucial cyclisation are described.

18 citations