The cyclization of bicyclooctane systems to tricyclooctane systems is discussed with particular reference to stereochemical aspects as encountered during the total syntheses of ishwarane and trachylobane. Of special interest are the homoallylic cyclizations. A third, convenient synthesis of trachylobane via a reductive homoallylic cyclization is reported.

No abstract

Selective thioketalization of a mixture of keto esters 5 and 6 resulted in the exclusive formation of thioketal7 and complete recovery of keto ester 6 . Lithium aluminum hydride reduction of thioketal7 followed by Moffatt oxidation of the resulting alcohol 8 gave aldehyde 10 which on treatment with a mixture of cis-and tratls-1-propenyl magnesium bromide afforded trarrsalcohol 11 and its cis isomer 12. Manganese dioxide oxidation of alcohol 11 followed by desulfurization gave trntu-2-damascone (3). Similarly, alcohol 12 was converted to cis-adamascone (4). HSING-JANG LIU, HINGCan. J. Chem. 56, 1368Chem. 56, (1978.La thiocCtalisation selective d'un melange des ceto esters 5 et 6 conduit a la formation exclusive du thiocCtal7 et une recuperation complete du cCto ester 6. La reduction par LiAIH, du thiocetal 7, suivie par une oxydation de Moffatt effectuke sur l'alcool 8, fournit I'aldthyde 10 qui, par traitement avec un mClange cis et trans des bromures de propene-1 yle magnksium, donne naissance a l'alcool trans-11 et i son isomere cis-12. L'oxydation de I'alcool 11 par le dioxyde de manganese, suivie par une dCsulfurisation, permet d'obtenir I'a-damascone trot~s (3). De la mCnie maniere, on peut transformer I'alcool 12 en a-damascone cis (4).[Trad~lit par le journal] p-Damascenone (1) (1-5) and P-damascone (2) (2, 6) are highly odoriferous conipounds found in nature as trace components in the essential oils of several plant species. Because of their industrial importance and limited availability from natural sources, much attention ( I , 7-1 5) has been drawn to the synthesis of these ketones as well as their structurally related compounds which are of equal industrial interest. Several syntheses of trans-adamascone (3) and of cis-a-damascone (4) have previously been reported involving modifications of a-cyclocitral (1) 01. a-ionone (7,(11)(12)(13). I n this paper we describe a full account of an efficient synthesis of 3 and 4 without relay (16). (17) was adapted for its simplicity. Although it was reported that a single isomer was obtained, the BF,-catalysed condensation of acetone and ethyl acetoacetate under the described conditions gave, in o u r hand, a mixture of the desired keto ester 5 and its positional isomer 6 in a ratio of ca. 2 : 1. Attempts t o separate these t w o isomers by distillation were fruitless. A similar mixture was also obtained previously by Surmatis et a/. (20), using zinc chloride a s a catalyst. They found that 6 could be selectively hydrolyzed by heating the mixture with zinc chloride in ethanol a n d water to facilitate the separation of 5. Efforts made toward this end did not result in substantial change of the mixture composition. The desired compound 5 could however be separated from its isomer 6 by extensive column chromatography as noted (20) a n d its thioketalization gave rise t o the thioketal 7 in quantitative yield. A niore convenient procedure involves the treatment of the mixture of 5 and 6 with 1,2-ethanedithiol and boron trifluoride etherate a t 0°C for 7 h. Under t...

A convenient and efficient method for the THE tricyclo[3,2,1,02~7]octane system is a novel structural construction of the tricyclo[3,2,l,0~~7]octane system, feature of a group of sesquiterpenoids related to the naturinvolving a homoallylic cyclization, is reported ; the ally occurring hydrocarbon ishwarane (1)l and of a larger application of this method results in a considerably group of diterpenoids of which the naturally occurring simplified and more efficient synthesis of trachylobane. parent hydrocarbon is trachylobane (11) . % We have

Aus Acetessigester und Aceton entsteht ein 2:l‐Gemisch der Kondensate (III) und (IV), die durch die Reaktion mit Äthandithiol getrennt werden können.