Laurene, synthesis

Lapworth, Arthur, 707 Lard, composition of, 1062 Latex, rubber from, 245 vulcanization of, 245-246 Laurene, synthesis of, 875 Laurie acid, structure of, 1062 LDS0, 25 table of, 26... 

The final step in an attempted synthesis of laurene, a hydrocarbon isolated from the marine alga Laurencin glandulifera, involved the Wittig reaction shown. The product obtained, however, was not laurene but an isomer. Propose a mechanism to account for these unexpected results. 

The palladium-catalyzed reductive coupling reactions were used in the synthesis of several natural products, including laurene [75], ceratopicanol [80], and dihydrostreptazolin 141 [81]. The cyclization leading to dihydrostrepta-zolin shown in Eq. 26 highlights the diastereoselectivity and functional group compatibility seen with this catalytic system. 

Cyclopropylidene alcohols have been used in the asymmetric synthesis of 2-hydroxymethylcy-clobutanones via tandem asymmetric epoxidation and enantiospecific rearrangement (Table 5).5 5 The yields and enantiomeric excesses were high. The method was used in the enantioselective syntheses of ( + )- and (—)-a-cuparenone55 and ( + )-laurene.56... 

In cases where the E-value is rather low, repeated resolutions may be required to supply the desired enantiomers in high ees. The synthesis of both enantiomers of the marine natural product laurene 13 provides an illustrative example. Here, the racemic cyclopentylcarbinol 12 is acylated with vinyl acetate in hexane catalyzed by CRL (E 35) to provide the remaining substrate in high . Chemical hydrolysis followed by repeated CRL-catalyzed acylation and then chemical hydrolysis provides the other enantiomer of the alcohol (Scheme 4.11) [52]. 

The first naturally occurring member of the class of fenestranes is the diterpene lauren-l-ene (27), isolated in 1979 from the essential oil of Dacrydium cupressinum. The intermediate (26) for Wender s stereocontrolled synthesis of (27) is readily accessible by attack of KOH on the tosyloxy ketone (25) to give, via fragmentation, a carboxylate anion which undergoes immediate ring closure to the lactone (26 Scheme 12). 

The sequence of intramolecular photocycloaddition-cyclobutane fragmentation has been used by Crimmins in an excellent manner for the synthesis of pentalenenes and the even more sophisticated lauren-l-ene (27). The latter synthesis was accomplished in 27 steps from cyclopentenone U66). One of the key steps is the reductive cleavage of the tetracyclic cyclobutane (167), followed by hydrogenation of the resulting P,7-unsaturated ester to give keto ester (168 Scheme 57). 

The final step in an attempted synthesis of laurene, a hydrocarbon isolated... 

Deoxygenation (6, 98, 7, 54 8, 79-80 9, 97-99). Taber and Anthony1 have used Kubulka s deoxygenation reaction for a stereoselective synthesis of (+)-laurene (2) from the unsaturated aldehyde (1). Some other methods are somewhat less selective. 

Coutrot, P, Lauren o, C.. Petrova. J., and Savignac, P, a-Chlorination and carbonyl olefination. Synthesis of phenyl 1-chloro-l-alken-l-yl sulfides. Synthesis, 107, 1976. 

A similar intramolecular hydroacylation is possible via reductive radical aldehyde addition to alkencs and subsequent oxidation of the resulting alcohol. Based on this observation a strategy towards the synthesis of cuparenoids [( )-a-cuparenone. ( )-epilaurene and laurene] was... 

Recent investigations have shown that )8-addition of phenyl groups to a,/S-unsaturated cyclopentenones followed by a-alkylation of the intermediate enolate produces the thermodynamically less stable c/s-2,3-disubstituted product. This new procedure has led to an alternative synthesis of the cyclo-pentanone derivative (145) which had been used previously as an intermediate in the synthesis of ( )-laurene (146). 

Paquette was one of the first to apply the Wacker oxidation in the total synthesis. In his synthesis of 18-oxo-3-virgene, a constituent of the waxy surface resins of tobacco, a Wacker oxidation was deployed to convert a terminal alkene to the corresponding methyl ketone.59 In an efficient total synthesis of ( )-laurene (77), alkene 75 was oxidized to keto-aldehyde 76 at ambient temperature.60 In Smith s total synthesis of calyculin, a modified Wacker oxidation with substoichiometric cupric acetate transformed terminal alkene 78 to methyl ketone 79 without concurrent acetonide hydrolysis.61,62... 

Enantioselective Synthesis of (+)-Laurene via Ring-Expansion of 1 -Vinylcyclobutanol... 

Laurene is a sesquiterpene isolated from marine red algae Laurencia elate. It possesses an exo-methylenecyclopentane core with two contiguous stereocenters, one of which is quaternary (Scheme 8.8). Fukumoto et al. reported the enantioselective synthesis of (-l-)-laurene by ring-expansion of 1-vinylcyclobutanol induced by an electrophilic palladium(II) catalyst [28]. 

Figadere B, Harmange J-C, Laurens A, Cave A. Stereospecific synthesis of (-I-) muricatacin a biologically active acetogenin derivative. Tetrahedron Lett. 1991 32(51) 7539-7542. 

Srikrishna, A. and Sunderbabu, G. (1989) Total synthesis of ( )-laurene and epilaurene by radical cyclisation reaction. Tetrahedron Lett., 30, 3561—3562. 

Nemoto, H., Nagamochi, M., and Fukumoto, K. (1992) The first enantioselective total synthesis of (+)-laurene. J. Chem. Soc. Chem. Commun., 1695—1697. 

Schwarz, J.B. and Meyers, A.l. (1995) Synthesis of vicinal stereogenic tertiary and quaternary centers using chiral bicyclic lactams and diastereoselective protonation. Asymmetric synthesis of (+)-laurene. J. Org. Chem., 60, 6511-6514. 

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