Tandem Wittig–intramolecular Diels–Alder cycloaddition of ester-tethered 1,3,9-decatrienes under microwave heating

Intramolecular Diels–Alder (IMDA) cycloaddition of the ester-tethered 1,3,9,-decatrienes possessing a carbonyl substituent at C10 has been investigated under controlled microwave heating (MeCN, 180 °C) to afford a variety of 3,4,4a,7,8,8a-hexahydroisochromen-1-ones in 53–89% yields and in 64:36–79:21 ratios for the cis and trans isomers. Under the same microwave heating conditions, a tandem Wittig–IMDA cycloaddition, starting from the α-bromoacetates of 3,5-hexadien-1-ols and glyoxalate/phenylglyoxal hydrates in the presence of PPh3 and 2,6-lutidine, has been demonstrated, furnishing 3,4,4a,7,8,8a-hexahydroisochromen-1-one adducts in 73–91% yields in favor of the cis isomers. During this tandem process, three consecutive carbon–carbon bonds in the end products were efficiently formed with the aid of microwave irradiation within short reaction times.