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.