Carbocationic cyclopropanation using tin

gamma-Effects of group 14 elements such as silicon and tin is discussed with the emphasis on the comparison with P-effects. Based on the striking gamma-effect of tin, cyclopropantion reactions of alkenes using organotin compounds have been developed. Using allyl group 14 element compounds as alkenes, intramolecular competition between beta-elimination and gamma-elimination of group 14 elements has been Studied. Intermolecular competition has also been examined using the reaction of allyl- and homoallyl group 14 element compounds with electrophiles. As an application of the present method in organic synthesis, intramolecularization of cationic cyclopropanation based on in-situ transacetalization to form unique cyclopropane Structures is demonstrated.