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A formal total synthesis of the marine sesquiterpene (±)-9-isocyanoneopupukeanane starting from the readily available monoterpene carvone has been accomplished employing a combination of intermolecular Michael addition–intramolecular Michael addition reaction and an intramolecular rhodium carbenoid C–H insertion reaction as key steps, and identifying the isopropenyl group as a masked hydroxy group.

An enantiospecific first total synthesis of (+)-trans-α-himachalene, one of the eight male specific sesquiterpenes isolated from the crucifer flea beetle Phyllotreta cruciferae, starting from the readily and abundantly available monoterpene, (R)-carvone, is described.

A stereoselective total synthesis of (+)-α-herbertenol starting from the allyl alcohol 12, readily available in three steps from the monoterpene (R)-limonene, is described. Claisen rearrangement of the aryl allyl ether 10 and concomitant cyclisation furnished a 5:3 mixture of the tricyclic compounds 13 and 14. Degradation of the isopropenyl group followed by cleavage of the central ring and functional group manipulation transformed 13 into (+)-α-herbertenol (1b).

Enantiospecific construction of the bicyclo[4.3.0]nonan-8-one 17 employing a lithium and liquid ammonia mediated carbanion cyclisation of the $\delta$-methyl-$\delta$,$\varepsilon$-unsaturated ester 13, and its elaboration to the tricyclic framework of the marine sesquiterpenes spirodysins are described.

Lithium–liquid ammonia mediated carbanion cyclisation of δ,e-unsaturated esters leading to cyclopentanes, fused as well as spiro, via annulation is described.

[reaction: see text] A simple and efficient approach for the BC and AB ring systems of the novel diterpenes guanacastepenes and rameswaralide starting from the readily and abundantly available monoterpene (R)-carvone employing RCM reaction as the key step is described.

A four-step cyclopentenone annulation reaction of allylic alcohols employing a 5-exo-trig radical cyclisation reaction of mixed allyl methyl ketals of bromoacetone as the key step is described. The annulated product 12b obtained from 2,3-dimethylcyclohexenol has been further elaborated into (±)-epibakkenolides employing a 5-exo-dig radical cylisation reaction based α-spiro-β-methylene-γ-butyrolactone annulation methodology.

A simple and convenient tandem methodology for the enantiospecific generation of functionalised bicyclo[3.3.1] nonanes 9,14-18, via intermolecular alkylation of Michael donors with 10-bromocarvones 7, 10 and 11, followed by intramolcular Michael addition, is achieved. An unsuccessful attempt for the extension of the methodology for a possible short enantiospecific approach to AB-ring system 22 of taxanes via the allyl bromide 21, is also described.

A methodology for the synthesis of compounds containing the cis-anti-cis fused triquinane system has been developed starting from tricyclo[5.2.1.02,6]deca-4,8-dien-3-(exo)ol 6 involving Ireland ester Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions as key steps.

Total synthesis of α-herbertenol, β-herbertenol and 1,13-herbertenediol, employing a Claisen rearrangement and ring-closing metathesis as key reactions for the generation of the cyclopentane containing vicinal quaternary carbons, has been described.

The first enantiospecific synthesis of (+)-cis,anti,cis-1,8,12,12-tetramethyl-4-oxatricyclo[6.4.0.02,6]dodecan-3-ol (+)-1g, an enantiomer of natural thapsane isolated from Thapsia villosa var minor, is accomplished starting from (R)-carvone, which revises the absolute stereochemistry of natural thapsanes.

A total synthesis of 1,14-herbertenediol via 11-epi-herbertenolide, and a formal total synthesis of tochuinyl acetate and dihydrotochuinyl acetate, employing a ring-closing metathesis reaction based methodology, are described.

The title compound I (24-(S)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P212121 with Z=4. The unit cell dimensions are a=6.701(2)A, b=11.506(8)A, c=32.183(4)A, V=2481(2)A3, Dcal=1.077 Mg/m3. The title compound II (24-(R)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P212121 with two molecules per assymetric unit and with Z=8. The Unit cell dimensions are a=10.954(2)A, b=21.757(6)A, c=21.130(7)A, V=5035.0(2)A3, Dcal=1.062 Mg/m3. In compound I and in both the molecules of compound II, the rings A, B & C are in chair conformation and the five membered ring D is in envelope conformation. The priority sequence attached to the chiral carbon C24 has “S” designation in compound I and “R” designation in compound II. The structures are stabilized by C-H…O and O-H—O hydrogen bonds.

An enantiospecific approach to mayurone and thujopsenes, sesquiterpenes containing three contiguous quaternary carbon atoms, starting from (R)-carvone (8), is described. (S)-3,4,4-Trimethylcarvone (7), obtained from (R)-carvone, was transformed into the bicyclo[2.2.2]octanone 13 via regioselective intramolecular alkylation of the allyl bromide 11. Regioselective ozonolysis and Criegee fragmentation of the bicyclic ketone 13 furnished the keto ester 14. Reductive deoxygenation followed by one-carbon homologation transformed the keto ester 19 into the ester 6. Intramolecular cyclopropanation of the diazo ketone 25, derived from the acid 5, furnished (−)-dihydromayurone (4), thus constituting a formal enantiospecific synthesis of mayurone and thujopsenes.

Formal total synthesis of both enantiomers of homogynolide-A, a sesquiterpene containing an α- spiro-β-methylene-γ-butyrolactone moiety fused to a bicyclo(4.3.0)nonane framework, is described. Thus, (R)-carvone was converted into both enantiomers of 3-methylcarvone 14. A reductive allylation, Wacker oxidation and intramolecular aldol condensation sequence transformed 3-methylcarvone into the hydrindanone 18. Regiospecific reduction of the enone followed by a three step degradation of the isopropenyl group converted the hydrindanone 18 into the dione 21, which on regioselective ketalisation furnished the key intermediate ketoketal 13. Methoxymethylene Wittig reaction followed by bromoacetalisation reaction transformed the ketoketal 13 into the bromoacetal 23. The 5-exo-dig radical cyclisation of the bromoacetal 23 followed by the hydrolysis and oxidation of the resultant spiroacetal 24 furnished a 1:4 mixture of the Greene's precursor ketospirolactone 12 and its spiroepimer 26.

Enantiospecific synthesis of the natural enantiomer of the marine sesquiterpene (-)-4-thiocyanatoneopupukeanane (6) is described. The bicyclo[2.2.2]octanecarboxylate 14, obtained from (R)-carvone via Michael-Michael reaction, was transformed into neopupukeananedione 12 by employing rhodium acetate catalyzed intramolecular C-H insertion of the diazo ketones 16 or 19 as the key reaction. Regioselective deoxygenation of the C-2 ketone transformed the dione 12 into neopupukean-4-one 10. Alternately, the keto ester 18 was also transformed into neopupukean-4-one 10 via regioselective deoxygenation of the ketone in 18 followed by intramolecular rhodium carbenoid C-H insertion of the diazo ketone 31. Finally, neopupukean-4-one 10 was transformed into (-)-4-thiocyanatoneopupukeanane 6 via the alcohol 32 and the mesylate 33.

Bromoacetalisation of the cinnamyl alcohols 7a-d, obtained from the corresponding benzaldehydes, generated the bromoacetals 10a-d. The 5-exo trig radical cyclisation of the bromoacetals 10a-d followed by one step hydrolysis-oxidation of the resulting cyclic acetals 11a-d furnished the title compounds 6a-d, respectively, well-established intermediates of a variety of lignans.

The title compound 1 ( 24-(S)-Hydroxycholesta-1,4-dien-3-one ) crystallises in orthorhombic space group $P2_12_12_1$ with z =4.The unit cell dimensions are a=7.5882(9)A, b=10.0745(14)A, c = 31.2553(23)A, $V =2389.4(5)A^3$, $D_{cal} =1.108Mg/m^3$. The title compound 2 ( 24-(R)-Hydroxycholesta-1,4-dien-3-one ) crystallises in monoclinic space group C2 with two molecules per assymetric unit and with Z=8. The Unit cell dimensions are a=16.752(4)A, b=12.578(4)A ,c=23.160(5)A, \beta =96.43(2)°, $V=4849.0(2)A^3$, $D_{cal}=1.092Mg/m^3$ . In compound 1 and in both the molecules of compound 2 the ring A deviates from planarity,the rings B & C are in chair conformation and the five membered ring D is in envelope conformation. The priority sequence attached to the chiral carbon C24 has 'S'designation in compound 1 and 'R'designation in compound 2. The structures are stabilized by O-H - O hydrogen bonds.

A Claisen rearrangement based methodology for spiroannulation of a cyclopentane ring to cyclic precursors and its application in the formal total synthesis of acorones 1 is described. Thus, Claisen rearrangement of 2-cycloalkylideneethanols 12 with 2-methoxypropene and a catalytic amount of mercuric acetate generates 4,4-substituted hex-5-en-2-ones 13. Ozonolytic cleavage of the terminal olefin in the enones 13 and intramolecular aldol condensation of the resulting keto-aldehydes 14 furnishes the spiroannulated compounds 15.

The first enantiospecific synthesis of a thapsane, containing three contiguous quaternary carbon atoms, is accomplished starting from R-carvone. An intramolecular alkylation and an intramolecular diazoketone cyclopropanation reaction were employed for the stereo- and regiospecific generation of three contiguous quaternary carbon atoms present in the thapsane framework.

A simple and direct approach to both enantiomeric series of A-ring derivatives of 1α,25-dihydroxyvitamin D 3 and the corresponding 1α,3α-derivatives, starting from the abundantly available R -carvone, is described.

Two enantiospecific routes to (+)-valerane starting from (R)-carvone, using a combination of Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions for the stereoselective generation of the vicinal stereogenic quaternary carbon atoms, are described. Thus, orthoester Claisen rearrangement of 3-methylcarveol 6 furnishes the ester 9 containing the first quaternary carbon atom. Intramolecular cyclopropanation of the diazo ketone 10 derived from the ester 9, followed by regioselective reductive cyclopropane cleavage, generates the hydrindanone 11 containing all stereocentres of valerane. Ring expansion of the hydrindanone to tetralone and further reductions transform 11 into (+)-valerane 2. In another direction, homologation of the acid 5 followed by intramolecular cyclopropanation of the diazo ketone 24 and regioselective cyclopropane ring cleavage lead to valerenone 25, which is transformed into (+)-valerane.

We have synthesized four different types of dimesogenic compounds involving the cholesteryl moiety as one of the mesogenic constituents, and have investigated their liquid crystalline properties. The molecular structures of these dimesogens have been confirmed by spectral analyses; they exhibit a rich polymorphism, as revealed by optical microscopic and differential scanning calorimetric observations. The studies show that the mesomorphic behaviour is sensitive to the nature of the terminal alkyl chains, and to the structure of the 'second mesogen' that is attached to the cholesteryl unit through a polymethylene spacer.

Synthesis of chiral bicyclo[4.3.1]decanes via an intramolecular acid catalysed type II ene reaction of chiral (5-isopropenylcyclohex-2-enyl)acetaldehydes derived from (R)-carvone is described. (C) 1999 Elsevier Science Ltd. All rights reserved.

A formal total synthesis of (±)-homogynolide-B, a sesquiterpene containing an α-spiro-β-methylene-γ-butyrolactone moiety spirofused to a bicyclo[4.3.0]nonane framework, is described. Thus, Hagemann’s ester 11 was converted into the allyl alcohol 16 in three steps. One-pot Claisen rearrangement of the allyl alcohol 16 and 2-methoxypropene in the presence of a catalytic amount of propionic acid afforded a 3∶2 epimeric mixture of the ketone 15 and further rearranged product 19. Ozonolysis followed by intramolecular aldol condensation and hydrogenation transformed the enones 15a,b into the key intermediate keto ketals 13a and 13b. Methoxymethylene Wittig reaction followed by bromoacetalisation converted the keto ketal 13a into the radical precursor bromo acetal 22a. The 5-exo-dig radical cyclisation of the bromo acetal 22a, followed by acid catalysed hydrolysis and oxidation, led to the keto spirolactone 12, Greene’s precursor of homogynolide-B. The same sequence transformed the keto ketal 13b into a 3∶2 mixture of the spirolactones 12 and 25, which on equilibration furnished the spirolactone 12. The stereostructure of the keto spirolactone 12 was unambiguously established by single-crystal X-ray diffraction analysis.

Details of the first total syntheses of the sesquiterpenes myltayl-8(12)-ene and 6-epijunicedran-8-ol are described. The aldehyde 13, obtained by Claisen rearrangement of cyclogeraniol, was transformed into the dienones 12 and 18. Boron trifluoride–diethyl ether mediated cyclization and rearrangement transformed the dienones 12 and 18 into the tricyclic ketones 16 and 17, efficiently creating three and four contiguous quaternary carbon atoms, respectively. Wittig methylenation of 16 furnished (±)-myltayl-8(12)-ene (11), whereas reduction of the ketone 17 furnished (±)-6-epijunicedranol (23).

First total syntheses of the tricyclic sesquiterpenes mentioned in the title containing a benzo-fused 2,8-dioxabicyclo[3.2.1]octane framework, confirming the structures of the natural products, are described.

Synthesis of the chiral bicyclic ketone mentioned in the title starting from R-carvone, and its elaboration to 7-epibakkenolide-A is described. Conjugate addition of dimethyl copperlithium to R-carvone followed by alkylation of the intermediate enolate generated the allylated compound 6, which was transformed into the diketone 12 via a sequence of reactions comprising regiospecific Wacker oxidation, ozonation-Criegee rearrangement as key reactions. Intramolecular aldol condensation followed by catalytic hydrogenation converted the diketone 12 into the bicyclic ketone (+)-3, the optical antipode of the compound derived from the sesquiterpenes bakkenolide-A and fukinone. A 5-exo-dig radical cyclisation based strategy transformed the bicyclic ketone 3 into chiral 7-epibakkenolide-A.

Enantiospecific synthesis of functionalised chiral C-ring derivatives of taxanes, starting from R-carvone, is described.

Details of the first total synthesis of the marine natural product dihydrotochuinyl acetate is described. Cyclopentenone annulation of p-methylacetophenone via a Claisen rearrangement-Wacker oxidation based sequence generated the cyclopentenone 3, a known precursor for the sesquiterpenes cuparene, laurene, α-cuparenone and β-cuparenones. Conversion of the ketone moiety into a carboxylate followed by stereoselective alkylation and reduction transformed the cyclopentenone 3 into the primary alcohol 19. Birch reduction of the alcohol 19 followed by acetylation furnished (±)-dihydrotochuinyl acetate, whereas direct acetylation of 19 furnished (±)-tochuinyl acetate.

The first enantiospecific total synthesis of the sesquiterpene (+)-pinguisenol, the optical antipode of the natural product, and the analogues (−)-pinguisen-10-one and (+)-pinguisen-8,10-dione, starting from R-carvone are described.

Reaction of the bromoketals 3, 7a-g and 11 with tri-n-butyltin chloride and sodium cyanoborohydride in the presence of a catalytic amount of AIBN furnished the ethers 5, 8a-g and 13 via a tandem sequence comprising of a radical cyclisation reaction and tri-n-butylhalostannane and sodium cyanoborohydride mediated reductive demethoxylation of the resulting cyclic ketals.

Photochemical oxadi-π-methane rearrangement (1,2-acyl shift) of the chiral bicyclo[2.2.2]oct-5-en-2-ones 2 and 3 furnishes the tricyclic ketones 5 and 6 , whereas the 1,3-acyl shift generates the cyclobutanones 7 and 8 respectively.

Reaction of the methoxyenones 3 and 11 with an excess of boron trifluoride etherate furnishes cleanly the chiral bicyclo[2.2.2]octa-5,7-dien-2-ones 9 and 12 respectively.

Synthesis of chiral tricyclo[3.2.1.02,7]octanes by efficient and exclusive 3-exo-trig radical cyclisation of either a bicyclo[3.2.1]oct-6-en-2-yl radical or a bicyclo[2.2.2]oct-5-en-2-yl radical is described. Reaction of the methoxy enones 7a–c with boron tribromide at low temperature furnishes the bicyclo[3.2.1]octenyl bromides 9a–c and 10a–c along with varying amounts of 8a–c, whereas the methoxy enone 7d provides the unrearranged bicyclo[2.2.2]octenyl bromide 8d. Treatment of the homoallyl bromides 9a–c and 10a–c and 8d with tributyltin hydride and AIBN generates, exclusively, the tricyclic ketones 15a–d.

Starting from the monoterpene R-carvone, enantiospecific total synthesis of the spirosesquiterpenes (+)-dihydroerythrodiene, (+)-dihydrospirojatamol and (+)-dihydroepispirojatamol is described.

The first total synthesis of a bioactive metabolite, isolated from the fungi Acremonium sp. HKI 0230, containing a cyclopentaspirobenzofuran carbon framework, employing an Ireland ester Claisen rearrangement and RCM reaction based strategy has been accomplished.

Efficient total syntheses of the herbertane sesquiterpene title compounds have been accomplished employing an Ireland ester Claisen rearrangement and ring-closing metathesis reaction sequence based strategy for the construction of two stereogenic vicinal quaternary carbon atoms on a cyclopentane.

The presence of an isopropenyl group at the C-1 position of a 3-isopropenylcyclohexaneacetaldehyde failed to generate the spiro[4.5]decane and produced only bicyclo[4.3.1]decanol. However, the presence of a methallyl group at the C-1 position of 3-isopropenylcyclohexaneacetaldehyde generated exclusively the spiro[5.5]undecanols.

A sequence of highly regio- and stereoselective intermolecular metatheses followed by ring-closing metathesis of an1-allyl-3-(3-butenyl)cyclohexanol led to a $C_{3}-symmetric$ head to tailcyclic trimer; a 24-membered macrocycle containing three inward directed hydroxyl groups creating a hydrophilic cavity.

The first enantioselective total synthesis of (-)-microbiotol and(+)-\beta-microbiotene, sesquiterpenes containing three neighboring quaternary carbon atoms belonging to the cyclocuparane group, starting from cyclogeraniol employing a Sharpless-Katsuki asymmetric epoxidation, a boron trifluoride etherate mediated epoxidere arrangement and an intramolecular diazo ketone cyclopropanation as key steps, is described.

A combination of Ireland ester Claisen rearrangement and ring-closing metathesis (RCM) reactions has been employed for efficient formal total syntheses of herbertene-1,13-diol and α-herbertenol, sesquiterpenes containing two vicinal quaternary carbon atoms on a cyclopentane ring.

Enantioselective synthesis of both the enantiomeric forms of the hydrindane derivatives mentioned in the title, potential chiral precursors in terpenoid synthesis, starling from R-carvone employing two different cyclopentannulation methodologies is described.

A general and simple methodology for spirocyclopentannulation of cyclic ketones (or 4,4-disubstituted cyclopentenones from acyclic ketones) and its application in the synthesis of the spirodienone 7 via a prochiral precursor constituting a formal total synthesis of (+/-)-acorone (6), are described.

A regiospecific reduction of quinolines (and 1,10-phenanthroline) into the corresponding 1,2,3,4-tetrahydro derivatives using a combination of sodium cyanoborohydride and boron trifluoride etherate in refluxing methanol is described. Under the same conditions indole and acridine reduced to the corresponding dihydroderivatives, whereas acyl group transfer from oxygen to nitrogen atom is also noticed in the case of 8-acyloxyquinolines.

A regiospecific and stereoselective total synthesis of the trisnorsesquiternene (±)-albene, via a prochiral precursor is described. The ortho ester Claisen rearrangement of the allyl alcohol, obtained in two regiospecific reactions from a Diels-Alder adduct, followed by hydrolysis of the resultant ester furnished an ene acid in a highly stereoselective manner. Anhydrous copper sulphate catalysed intramolecular cyclopropanation reaction of the diazo ketone derived from the ene acid, generated a cyclopropyl ketone. The regiospecific reductive cleavage of this cyclopropyl ketone resulted in a prochiral ketone. Finally, Shapiro reaction on the tosylhydrazone, derived from the latter ketone, furnished (±)-albene.

Irradiation of 4-aryl-4-alkylhex-5-en-2-ones (e.g. 1a) or 5-aryl-4-alkylhex-5-en-2-ones (e.g. 2a) adsorbed on montmorillonite K-10 in a commercial microwave oven furnishes the multialkylated naphthalenes (e.g. 3).