Reviewing the literature published to May 1985 L 2.1 2.2 I-Naphthoic Acids 7.6 Di hydrophenan threnones 8.1 Arylsilanes 8.2 Benzylsilanes 9.1 Hydrogenolysis of Nuclear Substituents 8 Reduction of Aryl-and Benzyl-silanes 9 Reductive Fission of Hetero-substituents 9.1.1 Simple Ethers 9.1.2 Deoxygenation of Phenols 9.1.3 Alkoxy-substituted Aromatic Acids and Ketones 9.2.1 Benzylic Alcohols 9.2.2 Benzylic Acetals 9.2.3 Benzylic Amines 9.2 Hydrogenolysis of Benzylic Substituents 10 Conclusion 1 1 References * This review was prepared to mark the occasion of the 70th birthday of Professor 2-Acetylnaphthalenes Birch on 3rd August 1985.

The structure (III) proposed for the hexacyclic alkaloid, himgaline, on the basis of chemical and spectroscopic characterization was confirmed by several partial syntheses of himgaline derivatives from de-N-methylhimbadine (alkaloid G.B. 13). The biogenesis of the Galbulimima alkaloids is discussed.

Abstract

The structures of himbadine (I) and its de-N-methyl derivative (II), alkaloid G.B. 13, proposed on the basis of chemical and spectroscopic characterization were confirmed by several partial syntheses from the ester alkaloid, himandrine (III), of known structure.

The acid-catalysed reactions in weakly nucleophilic environments of 2-diazoacetyl-l,2,3,4-tetrahydronaphthalene (ll), of 6-diazoacetyl-5,6,7,8-tetrahydro-2-naphthol (2), of 6-diazoacetyl-5,6,7,8- tetrahydro-2-naphthyl methyl ether (3) and its 2,8 and 2,5 isomers (14) and (17), and of 6-diazo- acetyl-5,6,7,8-tetrahydro-6-trifluoroacetoxy-2-naphthyl methyl ether (9) have been studied. Several of the spirocyclohexa-2,5-dienone derivatives prepared thus, (4), (8) and (16), provide potential intermediates or models for the synthesis of tetracyclic diterpenoids.

Two successful and two unsuccessful synthetic routes are described for the conversion of commercially available fungal gibberellins to the antheridiogen GA73 methyl ester (5), originally isolated from gametophytes of the fern Lygodium japonicum. The more efficient route began with the Birch reduction of either the GA7 derivative (31) or methyl gibberellate 3,13-dimesylate (32) to give the ∆1(10),16-diene acid (33), which was converted into the ∆1,9-diene acid (40) by means of a four step procedure. This intermediate could be selectively hydrogenated to the ∆9-ene derivative which underwent iodolactonization and then elimination of HI to afford enone (29), Wittig methylenation of which furnished the target antheridiogen (5). In addition, (29) was functionalized at C12 by free radical bromination to give access to the 12β-hydroxy derivative of (5), i.e. (6), a new antheridiogen isolated from Lygodium circinnatum.

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