Approaches to the synthesis of cytochalasans. Part 5. Studies on the selectivity of the Diels‐Alder reaction leading to the tetrahydroiso‐indolinone sub‐unit

Abstract

SummaryThe stereo-and regiochemical course in the [2+ 4lcycloaddition of the chiral alkylidene malonic ester 1 to selected derivatives of (2 E, 4 E)-4-methyl-2,4-hexadien-1-01 (2:) and (2 E, 4 E)-Cmethy1-2,4-hexadien-1-a1 (12) has been investigated. The results are discussed on the basis of semiquantitative PMO theory.The thermally induced [2+ 4lcycloaddition of the alkylidene malonic ester 1 to (2 E, 4E)-4-methy1-2,4-hexadien-l-o1 (2) has been shown to be followed immedi- The numbering of the sub-units corresponds to that used for the cytochalasans 121.

Molecular Basis of Cytochalasan Biosynthesis in Fungi: Gene Cluster Analysis and Evidence for the Involvement of a PKS-NRPS Hybrid Synthase by RNA Silencing

“…It has long been a matter of speculation if this intriguing tricyclic ring system is generated by a Diels−Alder-type reaction. − However, to date there has not been a single report on the molecular basis of cytochalasan biosynthesis. To shed more light onto the biogenesis we sought to clone the responsible genes.…”

Approaches to the Synthesis of Cytochalasans Part9. A versatile concept leading to all structural types of cytochalasans

“…Intermolecular [2 + 41 cycloaddition of olefin 13 and diene 14 at 140" in o-xylene gave the two regioisomers 15 (50%) and 16 (32%). The assignment of their structures and configuration was possible beyond any doubt by 'H-NMR decoupling experiments as previously described in a similar case [7]. The desired isomer 15 was converted to compound 4a in 40% yield by cleavage of the silyl ether with TsOH in MeOH (-+17), followed by bromination with CBr,/Ph,P in CH2Cl,.…”