Tandem Diels‐Alder Reactivity Controlled by Remote Substituents. Regioselective synthesis of linearly annellated six‐membered ring systems from (1RS,5SR,6RS,7SR)‐6,7‐bis(chloromethyl)‐8,9‐dimethylidene‐2‐oxabicyclo[3.2.2]nonan‐3‐one. Crystal structure of (1RS,5RS,6SR,11RS)‐6,7‐bis(chloromethyl)‐3‐oxo‐2‐oxatricyclo[7.4.0.^1,5]tridec‐8‐en‐11‐yl methyl ketone

Abstract

ChemInform Abstract The rate constants of the two successive Diels-Alder additions of a given dienophile, e.g. methyl vinyl ketone, to the tetraenes (I) (synthesis described) or (V) are found to be nearly the same, thus making difficult the isolation of monoadducts in reasonable yields. Moreover, (I) and (V) and their corresponding adducts have a strong tendency to polymerize. Therefore, the synthetic potential of these compounds is very limited. In contrast, the diene (VI) is found to add strong dienophiles with good regio-and stereoselectivity. Reaction of (VI) with methyl vinyl ketone (IX) yields, depending on the quenching temp., the adduct (VII) or the ketone (VIII) (X-ray analysis: space group P21/n; Z=4). Compound (VII) is transformed to the triene (X) which adds to non-sym. dienophiles such as (XI) and (XIII) with good regioselectivity to give the polycycles (XII) and (XIV)/(XV), resp., which represent suitable anthracyclinone precursors.

Synthesis of β-, γ-, δ-, ..., ω-Halogenated Ketones and Aldehydes

“…A chromium-based oxidant for primary or secondary alcohols, tolerant toward acid-sensitive functionalities, is the Collins−Ratcliff reagent (CrO 3 ·2py in CH 2 Cl 2 ). This complex was used by Vogel and co-workers to convert chlorinated bicyclo[2.2.2]octan-2-ol derivative 800 into the corresponding octanone 801 (Scheme ) …”

“…As described in the section on γ-halogenated compounds, polychlorinated bicyclo[2.2.2]octan-2-one 801 has been prepared by Collins−Ratcliff oxidation of the parent alcohol (Scheme ) …”