Lactone synthesis by manganese(III)-mediated oxidative cyclization of allylic .beta.-diesters

Synthesis of (±)‐Merrilactone A by a Desymmetrization Strategy

“…In summary, we achieved a concise synthesis of racemic merrilactone A in 15 steps from known dilactone 2 , and 18 steps total from commercially available diethyl methylmalonate . This work joins the shortest routes reported for synthesizing racemic merrilactone A, and it is highlighted by the strategic desymmetrization of C s ‐symmetric dilactone and intramolecular hydroacylation to ensure a dexterous merging of the A‐ and B‐rings of merrilactone A.…”

“…The later routes required considerable elaboration to reveal the A‐ring lactone afterwards, due to the inert nature of 3,4‐dimethylfuran‐2(5 H )‐one toward cycloaddition . However, we designed a general rapid entry to this rather challenging structural motif of 1 and other sesquiterpenes in the subgroup by desymmetrizing a readily available C s ‐symmetric dilactone 2 (Scheme ). The controlled mono‐ring‐opening of dilactone 2 would not only allow direct access to the A‐ring γ‐lactone with the desired stereochemistry of angular dimethyl substituents ( 2 → 5 ), but also set out a facile annulation precursor for the B‐ring ( 5 → 4 ).…”

Manganese(III) Acetate-mediated Oxidative Cyclization of a-Methylstyrene and trans-Stilbene with b-Ketosulfones

“…As Mn(OAc) 3 -mediated intermolecular cyclopropanation with trans -stilbene or a similar 1,2-disubstituted alkene has never been reported, the structure of cyclopropane 16 was established by X-ray diffraction analysis (Figure 1). As specified in previous studies [44], Mn(OAc) 3 mediated cyclopropanation should come from the cation C (Schem 4), which reacted rapidly with the enolic form of β-ketosulfone to close the cyclopropane ring.…”

“…To our knowledge, few studies have reported intramolecular cyclopropanation under Mn(OAc) 3 reactivity [42,43,44,45], and only one reported intermolecular reactions between oxabenzonorbornadiene and dimedone [46]. As Mn(OAc) 3 -mediated intermolecular cyclopropanation with trans -stilbene or a similar 1,2-disubstituted alkene has never been reported, the structure of cyclopropane 16 was established by X-ray diffraction analysis (Figure 1).…”

Mechanisms of Mn(OAc)3-based oxidative free-radical additions and cyclizations

“…Oxidative cyclization of 100 affords 101 , which is rapidly oxidized to radical 102 . Radical 102 gives intractable material if R = Me, but affords 66% of 103 if R = crotyl 33. The lactone group makes the α-hydrogen of 101 much more acidic34 than those of 100 so that product lactone 101 is oxidized more rapidly than diester 100 .…”