novel Pd-catalysed cross-coupling reaction of allenylic carbonates with different gem-diborylalkanes was developed. Under mild reaction conditions, synthetically useful and versatile isoprenylboronates could be obtained selectively in moderate to high yields. Furthermore, the utility of the novel isoprenylboronate is demonstrated through isoprenylboration and homologation.
(±)-2-Pupukenone (4) has been synthesized, the key step being the intramolcular Diels-Alder reaction of the intermediate 13 to 14 (42%) and 15 (14%). The bromodiene 12 has been obtained from the reaction of α-isopropylidene-γ-lactone (Scheme 2) 12 with sodium phenylselenide and subsequent esterification to 9, oxidation and thermal elimination of which furnished 10. Reduction of 10 with diisobutylaluminimum