Mangalam S. Nair

A novel, versatile synthetic approach to linearly fused tricyclopentanoids via photo-thermal olefin metathesis

Abstract Fifteen examples of a new, speedy and general approach to linearly fused tricyclopentanoids bearing the tricyclo[6.3.0.0 2,6 ]undecane (triquinane) frame of high contemporary interest is delineated. The key concept in our synthetic sequence to triquinanes is the novel photo-thermal olefin metathesis of cheap, abundantly available Diels-Alder adducts of 1,3 cyclopentadienes and p-benzoquinones. Thus photolysis of endo -tricyclo[6.2.1.0 2,7 ] undeca-4,9-dien-3,6-diones ( 9a – 9j , 13a,b ) furnished pentacyclo [5.4.0.0 2,6 .0 3,10 .0 5,9 ]undecan-8,11-diones ( 10a – 10j , 14a,b ), which on thermal fragmentation of the cyclobutane ring gave cis , syn , cis -tricyclo [6.3.0.0 2,6 ]undeca-4,9-dien-3,11-diones ( 11a – 11j , 15a,b in just three steps and in exceptionally good yields. A few interesting transformations of the readily available parent bis-enone 11a which indicates its wider uses in syntheses, are described. Finally, a smooth thermal isomerisation of cis , syn , cis -bis-enones to cis , anti , cis -bis-enones is reported, which further enhances the scope and versatility of our synthetic theme.

Synthesis of Some Novel Heteropolyquinanes

Synthesis of structurally novel aza-and oxa-polyquinanes from the abundantly available cis,syn,cis-triquinane dione 1 via transannular nucleo-phillc additions is reported.

Synthesis of spheroidal C20-polyquinanes in a route towards dodecahedrane

An approach to the hydrocarbon dodecahedrane 1 has been formulated based on a retrosynthetic theme. The starting exo,exo-tetraquinane diester 9 was conveniently synthesized from the readily available C2v,-tetraquinane dione 5. Bis-cyclopentannulation of compound 9 employing the dichloroketene addition–ring-expansion methodology of Greene furnished the hexaquinane diester 12. The newly appended cyclopentanone rings in compound 12 were inverted via a three-step sequence involving dehydrogenation to bisenone 13, acetalisation to give compound 17, and catalytic hydrogenation to compound 18. Attempts to epimerise the exo,exo-diester functionality within the spheroidal cavity in the all-cis-hexaquinane dione diester 18 for the pivotal ‘molecular stitching’ step have so far proved unsuccessful. Cyclopentannulation reactions on Hedaya–Paquette ester 23 employing Greene methodology and the Pauson–Khand reaction have been carried out. Several interesting cyclisations and transannular reactions in the resulting polyquinanes have been observed.

Synthetic studies in quest of Platonic hydrocarbon dodecahedrane

In pursuit of Platonic hydrocarbon dodecahedrane1, a retrosynthetic theme indicated in scheme 1, was formulated. The precursor tetraquinanedione synthon5 was first designed through a photo-thermal olefin metathesis approach. The tetraquinanedione 5 was further elaborated toexo, exo-tetraquinane diester15 through carbonyl homologation, oxidation, esterification sequence, scheme 5. Bis-cyclopentannulation ofexo,exo-diester15 by Greene methodology delivered a functionalised C20-hexaquinane44, havingexo-annulated cyclopentane rings. Cyclopentane inversion was achieved by a set of reactions involving enone generation, double bond isomerisation and hydrogenation to give spheroidal (C2v)-C20-hexaquinanedione-diester47, the penultimate precursor of dodecahedrane 1. Several interesting transformations and rearrangements of polyquinanes are also described.

Design of a key synthon for dodecahedrane: (C2v)-C12-tetraquinanedione

A six-step synthesis of tetracyclo[7.2.1.04,11.06,10]dodeca-2,7-diene-5,12-dione (2) from the readily available starting materials 7-t-butoxynorbornadiene and 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene is described.

Synthetic design of a spherodial C18-oxa-hexaquinane system: model studies for the synthesis of dodecahedrane

A seven-step synthesis of all-cis-4-oxa-octadecahydrodipentaleno[1,2,3-cd:1′,2′,3′-gh]-pentalene-2,6-dione (3) from the readily available hexacyclic ether (4) is reported.