Formation of spiro ketolactones versus alkoxy radical fragmentation-promoted three-atom ring enlarged lactones from cyclic ketones

A dual pathway from readily available 2-allyl-2-carboethoxycycloalkanones 1 provides a new facile stereoselective synthesis either of functionalized spiro ketolactones 4 or of ring enlarged lactones 7 in one-step. Thus, iodination of 5–8-membered 2-allyl-2-carboethoxycycloalkanones 1a–d led, in excellent yields, to spiro ketolactones 4a–d, respectively, as single stereoisomers. On the other hand, iodination of 1a–d under alkoxy radical fragmentation conditions via incipient hemiketals produced the 8-, 9-, 10-, or 11-membered, three-atom ring enlarged, poly-functionalized lactones 7a–c as two stereoisomers and 8 as a single isomer.