Synthetic Approach to Diterpene Alkaloids — A Simple and Novel Synthesis of the A, B, C and D Ring Part from 1-Benzyl-1,2,3,4-tetrahydroisoquinoline

The synthesis of the A,B,C and D ring part ( 1 of diterpene alkaloid atisine (2) from 1-benzyl-1,2,3,4-tetrahydroisoquinoline (Q) by use of an intramolecular Diels-Alder reaction is described.Previously we1 reported a new construction of A,B,C and E ring part ($) of diterpene alkaloids, which had been correlated to atisine (k12, by an intramolecular Diels-Alder reaction of the g-quinodimethane ( derived from the benzocyclobutene ( k )and then a reduction of the resulting tricyclic compound ( 2 ) .Continuing a synthetic approach to diterpene alkaloids, we have been investigating a new construction of diterpene alkaloid ring system, and here report a simple synthesis of the A,B,C and D ring part of atisine (2) from 1-benzyl-1,2,3,4-tetrahydroisoquinoline ( Q j , easily available, using an intramolecular Diels-Alder reaction as a key step.