New Olefinic Cyclizations by Oxymetallation. Conversion of (−)‐elemol to (−)‐selina‐4α, 11‐diol (cryptomeridiol) and (−)‐guai‐1 (10)‐ene‐4α, 11‐diol

Abstract

Acetoxythallation of (-)-elem01 acetate (lb) yields a diacetate 2b which after treatment with lithium aluminium hydride gives (-)-guai-I (IO)-ene-4a, 1 1 -diol (2a). (-)-Elemol (la) is converted to (-)-selina4a, 1 1-diol (9, cryptomeridiol) by hydroxymercuration followed by reductive demercuration. ( + )-y-Elemene (5) similarly yields (+ )-selin-7 (1 l)-en-4a-ol (11, juniper camphor). The stereochemistry and mechanism of these metal salt-induced olefmic cyclization and their biogenetic implication are discussed.Oxymetallation is a useful tool for the functionalisation of olefins or other nucleophilic substrates [ 11. Thus oxymercuration followed by reductive demercuration represents a simple and convenient procedure for regiospecific (Markovnikovtype) hydration of olefins [2]. Oxythallation is another versatile synthetic method for the oxidation of many types of substrates [3]. Lead tetraacetate represents a classical reagent for the functionalisation of alkenes [4]. Electrophilic metal salts, such as those used in oxymetallation reactions, may also be useful reagents for olefinic cyclizations. There are a few interesting reports [5-111 on this subject (vide infru) although no systematic investigations have been carried out. Further studies in this field should provide useful synthetic tools for olefinic cyclizations or rearrangements and also give valuable information on the stereochemistry and mechanism of metallation reactions. In this paper we report some new regio-and stereospecific olefmic cyclizations induced by thallium (111) and mercury (11) salts.Results. -Treatment of elemol acetate 1 b with thallium (111) nitrate (TTN) in acetic acid for 20 min at room temperature gave a crude diacetate 2b, which was treated with lithium aluminium hydride to give the diol 2a in 63.5%

Hedycaryol – Central Intermediates in Sesquiterpene Biosynthesis, Part II

“…Also proximadiol, the anti‐spasmodic principle from Cymbopogon proximus , [92,93] was later shown to be identical to (−)‐ 12 [94,95] . Another interesting transformation that secures the absolute configuration of cryptomeridiol is the conversion of (−)‐ 2 into (−)‐ 12 by oxymercuration and reductive workup (Scheme 7C) [96] …”

“…[94,95] Another interesting transformation that secures the absolute configuration of cryptomeridiol is the conversion of (À )-2 into (À )-12 by oxymercuration and reductive workup (Scheme 7C). [96] The diol 12 is fairly widespread in the plant kingdom and has additionally been isolated from Artemisia pygmaea, [97] Magnolia obovata, [98] Drymis winteri, [99] Hedychium spicatum, [100] Thujopsis dolabrata, [101] Carissa edulis, [102] Chenopodium graveolens, [103] Chamaecyparis pisifera, [104] Juglans mandshurica [105] and Achillea clypeolata, [106] in all cases with a reported negative sign for the optical rotation. Compound (À )-12 was also obtained in a biotransformation of synthetic (+)-1 with a mortared root suspension of chicory.…”