δ-Sultone Formation Through Rh-Catalyzed C−H Insertion

Abstract

Rhodium-catalyzed reactions of sulfonate ester derivatives are biased strongly toward 1,6-insertion and thus offer a general method for assembling delta-sultones. Two protocols for staging this cyclization reaction are described, which capitalize on the unique ability of either diazo or iodonium ylide intermediates to form Rh-carbene species. The value of these heterocycles for fine chemicals synthesis is demonstrated in both reductive and oxidative reactions that make possible excision of the -SO3- moiety.

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

“…However, the necessity for precise selectivity among multiple C-H bonds in the substrate, still remains the key issue in this reaction and its application in synthesis. 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.…”

“…The use of Rh 2 (S-MEPY) 4 and Rh 2 (S-DOSP) 4 resulted in no selectivity. The use of a non-polar solvent (2,2-dimethylbutane) with Rh 2 (S-DOSP) 4 catalyst 10 provided the first glimpse of selectivity, although complications arose due to the poor solubility of the diazocompound in this solvent. Next, we explored the class of catalyst derived from a phthalimide protected aminoacid, 11 starting with Rh 2 (S-pttl) 4 , derived from tert-leucine.…”

“…The use of a non-polar solvent (2,2-dimethylbutane) with Rh 2 (S-DOSP) 4 catalyst 10 provided the first glimpse of selectivity, although complications arose due to the poor solubility of the diazocompound in this solvent. Next, we explored the class of catalyst derived from a phthalimide protected aminoacid, 11 starting with Rh 2 (S-pttl) 4 , derived from tert-leucine. This provided the first encouraging results, with the additional bonus of an increased yield of the product.…”

“…This provided the first encouraging results, with the additional bonus of an increased yield of the product. Following this, we attempted to optimize the catalyst structure by increasing and decreasing the size of the substituents at the aminoacid stereogenic center (using Rh 2 (S-ptad) 4 , 12 Rh 2 (S-nttl) 4 ), Rh 2 (S-ptpa) 4 , Rh 2 (S-nta) 4 ). All modifications failed to increase the enantioselectivity when compared to Rh 2 (S-pttl) 4 .…”

“…Following this, we attempted to optimize the catalyst structure by increasing and decreasing the size of the substituents at the aminoacid stereogenic center (using Rh 2 (S-ptad) 4 , 12 Rh 2 (S-nttl) 4 ), Rh 2 (S-ptpa) 4 , Rh 2 (S-nta) 4 ). All modifications failed to increase the enantioselectivity when compared to Rh 2 (S-pttl) 4 . Lowering the reaction temperature to 0°C provided a small increase in selectivity, at the expense of the yield, while a further decrease of temperature (to −20°C) had no effect.…”