Formation of six- versus five-membered cyclic sulfones by C–H insertion

Abstract

Selectivity of six- vs. five- membered ring formation in C-H insertion on alkylsulfonyl diazoacetates is sensitive to the substrate structure and catalyst used.

Catalytic asymmetric C–H insertion reactions of α-diazocarbonyl compounds

“…As seen in Table 26 (entries a-e), enantioselectivities of up to 98% ee were realised for the decomposition of various substituted α-diazosulfones. The trend towards preferential six-membered-ring formation for carbenoid synthesis of sulfur heterocycles, as previously observed by Novikov and co-workers, 152,153 was seen to be preserved, with all thiopyran products forming in a highly enantioselective fashion (94-98% ee) and with cis selectivity. …”

“…152 Such a finding was surprising, given the large preference in diazo decomposition reactions for the formation of five-membered-ring products. 6 This outcome has been rationalised, however, by the difference in bond lengths and bond angles observed around the sulfur atom which are thought to mimic the geometry of the sixmembered ring, 152,153 as was also observed for intramolecular C-H aminations. 154 The first, and only, report of the enantioselective production of sulfur heterocycles employing C-H insertion chemistry was published in 2009 by Maguire and co-workers for the C-H insertion reactions of α-diazosulfones (Table 26).…”

“…Indeed, only a minimum of reports exist documenting the successful synthesis of sulfur heterocycles via carbenoid chemistry and, until recently, such reactions have been realised only in a racemic fashion. [150][151][152][153] In 2007, Novikov and co-worker reported the selective formation of six-membered cyclic sulfonates and sulfones by C-H insertion. 152 Such a finding was surprising, given the large preference in diazo decomposition reactions for the formation of five-membered-ring products.…”

Enantioselective copper catalysed intramolecular C–H insertion reactions of α-diazo-β-keto sulfones, α-diazo-β-keto phosphine oxides and 2-diazo-1,3-diketones; the influence of the carbene substituent

“…12 For the first twenty years of research in this area the vast majority of carbocyclic rings formed were five membered, with some exceptions, [17][18][19] when the insertion occurs into the sulfonyl group rather than the carbonyl containing chain the presence of the sulfone alters the geometry of the C-H insertion transition state enabling access to six membered thiopyrans, and, where the six membered ring is not accessible, five membered sulfolanes (Scheme 1). 17,[20][21][22] Scheme 1 Copper catalysed C-H insertion reactions of α-diazo-β-oxo-sulfones. 22 The first catalytic asymmetric C-H insertion reaction was carried out in 1990 in which a cyclopentanone was generated in up to 12 %ee using a rhodium catalyst.…”

Asymmetric intramolecular C–H insertion of sulfonyldiazoacetates catalyzed by Rh(II)

“…As has been previously demonstrated, 3,4 rhodium catalyzed C-H insertion on diazosulfonates and diazosulfones exhibits an unusual selectivity, producing six membered cyclic products rather than the usually observed five membered compounds, as shown by the examples in Scheme 1. 5,6 After initial studies of this transformation we became in performing this reaction enantioselectively. Recently, an enantioselective version of this reaction was reported using chiral copper catalysts with excellent enantioselectivity and generally good yields.…”