Some applications of the intramolecular alkylation of α-diazomethyl ketones through metal-catalysed addition and insertion reactions, and acid-catalysed olefinic and aryl participations, towards the synthesis of a variety of complex polycyclic natural products have been briefly reviewed with special emphasis on the results reported from the authors’ laboratories. The possible mechanisms of the transition metal catalysed carbon-carbon bond forming reactions of carbenoids have been briefly discussed in the light of the recent literature.

Synthetic utility of trimethyl and triethyl orthoformates for carbon-carbon bond formation is briefly surveyed, particularly in relation to dialkoxymethylation, carbonyl transposition-homologation, and cycloalkenone annulation reactions recently reported from the authors’ and other laboratories. The complex mechanisms involved in the one-step and two-step annulations of rigid β,γ- and γ, δ-unsaturated ketones have been discussed.

Success of ring closure reactions of substrates having two terminal alkenes through olefin metathesis depends on a number of factors such as catalysts, nature and size of the rings to be formed and the substituents/functional groups present on the alkenes as well as at the allylic position. This article presents an overview of these influencing factors with illustrative examples.

An asymmetric route for the synthesis of highly functionalized 2,3-epoxy-syn-1,4-cyclohexane diol derivatives present in some polyketide natural products has been developed. The key step involves RCM of an appropriately constructed 1,7-dienol derived from D-mannitol to cyclohexane-1,4-diol followed by its stereoselective epoxidation.

Synthesis of a functionalized tricyclo[6.2.0.0^2,6]decane derivative in enantiomerically pure form, the core structure present in the natural products kelsoene and poduran, is described. The key steps involve a stereocontrolled copper (I)-catalyzed intramolecular [2+2] photocycloaddition of a 1, 6-diene prepared from D-mannitol to form a substituted bicyclo[3.2.0]heptane derivative and a ring closing olefin metathesis involving the vicinal substituents on the five-membered ring of the bicyclo[3.2.0]heptane derivative.

A convenient route for the synthesis of oxacyclobutapentalene, the tricyclic bridged core structure present in bioactive marine diterpene bielschowskysin and the polyketide hippolachnin A, is reported. The key steps involve ring closing metathesis of a triene derived from D-mannitol to produce selectively the dihydrofuran derivative instead of the cyclopentene derivative and a Cu(I)-catalyzed intramolecular [2+2]photocycloaddition of the dihydrofuran derivative.

Ring closing metathesis of acyclic trienes that can provide oxacycles or carbocycles has been investigated. It was found that a substituent on one of the alkene units determines the reaction course to provide either oxacycles or carbocyles exclusively irrespective of the ring size of the resulting compounds.

Development of a route for the synthesis of the core structure of galiellalactone is described. The key step involves a ring-closing enyne metathesis of an allyl propargyl ether to produce a dihydro furano diene with a latent dienophile. The dienophile, when generated from this latent functionality, underwent an in situ intramolecular Diels–Alder reaction to produce the tricyclic skeleton present in galiellalactone