Goverdhan Mehta

Tandem cyclization–cycloaddition reactions of rhodium generated carbenoids from α-diazo carbonyl compounds

The rapid generation of molecular complexity, in a controlled and predictable manner, is a contemporary theme in the practice of modern organic synthesis and finds application in accessing newer entities for the pharmaceutical industry. Efficiency, atom economy, regio-, stereo- and enantiocontrol, ready availability of starting materials and environmentally benign processing are some of the common concerns in any synthetic endeavor. Synthetic brevity is, however, central to the generation of molecular complexity in a resource-effective manner and, in order to attain that objective, two strategic options have been generally explored in recent years, one involving multicomponent reactions and the other involving reactions leading to multiple carbon-carbon bond formation through tandem processes. The latter approach involves recourse to reactions like multiple cycloadditions or cyclization–cycloaddition sequences in which many bonds are formed in a single mode operation and these cascade processes have an inherent advantage in expeditiously assembling polycyclic structures with proper stereochemical control.

Hybrid systems through natural product leads: an approach towards new molecular entities

Hybrid systems are constructs of different molecular entities, natural or unnatural, to generate functional molecules in which the characteristics of various components are modulated, amplified or give rise to entirely new properties. These hybrids can be designed from carefully selected components either through domain integration of key structural/functional features or via straightforward covalent linkages. Some of the recently reported hybrid systems based on steroid, carbohydrate, C60-fullerene platforms, amongst others, mainly crafted with the object of enhancement of the therapeutical spectrum, will be discussed.

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.

Recent chemistry of benzocyclobutenes

This review covers aspects related to the synthesis, reactions and applications of benzocyclobutenes.

Meroterpenoids—I : Psoralea corylifolia Linn.—1. Bakuchiol, a novel monoterpene phenol

Isolation and structure elucidation of a novel monoterpene phenol, bakuchiol, from the seeds of Psoralea corylifolia Linn, is described.

Ultrasound Promoted Dichloroketene-Olefin Cycloadditions

Abstract We have observed that olefin-dichloroketene 2+2 cycloadditions are accelerated by ultrasonic irradiation. Short reaction times, good yields, ambient reaction conditions and use of ordinary bench-top zinc instead of activated zinc (Zn-Cu couple) are the significant advantages of this procedure.

A new synthesis of corannulene

Flash vacuum pyrolysis of 2-substituted benzo[c]phenanthrene has been exploited as a pivotal step in a new, simple synthesis of the ‘bowl-shaped’ hydrocarbon corannulene 1.

Total synthesis of the novel angiogenesis inhibitors epoxyquinols A and B

The synthesis of the recently discovered angiogenesis inhibitors epoxyquinols A and B, having novel polyketide derived dimeric structures, has been accomplished from the readily available Diels–Alder adduct of cyclopentadiene and p-benzoquinone through a short, simple and flexible strategy that is diversity oriented and can be adapted to an asymmetric variant.

Oxa-bowls: The pentaoxa[5]peristylane

The first synthesis of parent pentaoxa-[5]-peristylane, from a readily available and stereochemically well-defined norbornene precursor, employing a cascade of intramolecular acetalizations as the stratagem, is reported.

Total synthesis of novel xanthone antibiotics (±)-cervinomycins A1, and A2

Abstract A total synthesis of novel heptacyclic antibiotics cervinomycin A1 1 and A2 2 following a convergent approach is reported. The cornerstone of our strategy was the construction of the central ring D through photochemical electrocyclization. The oxazolo-isoquinolinone fragment (ABC rings) 7 and the xanthone fragment (EFG rings) 8 were assembled through relatively straightforward synthetic protocols and coupled through a Wittig reaction to give 6 and set up the key photocyclization. Our successful approach to 1 and 2 can be readily adapted to the synthesis of analogues of these interesting antibiotics.