Synthesis of vinyliodides: progress toward the total synthesis of a jatrophane diterpene

Reactions of Allylmagnesium Reagents with Carbonyl Compounds and Compounds with C═N Double Bonds: Their Diastereoselectivities Generally Cannot Be Analyzed Using the Felkin–Anh and Chelation-Control Models

“…Other examples confirm that additions of allylmagnesium reagents to α-alkoxy aldehydes proceed with seemingly no stereoselectivity (Scheme 55). 139 Recent experiments suggest a possible explanation for why α-alkoxy aldehydes are not generally able to undergo chelation control with any Grignard reagent. Competition experiments using THF as solvent revealed that no rate acceleration occurred for additions to an aldehyde capable of forming a chelated intermediate (138) versus an aldehyde that cannot (139) for either allyl-or methylmagnesium chloride (Scheme 56).…”

“…139 Recent experiments suggest a possible explanation for why α-alkoxy aldehydes are not generally able to undergo chelation control with any Grignard reagent. Competition experiments using THF as solvent revealed that no rate acceleration occurred for additions to an aldehyde capable of forming a chelated intermediate (138) versus an aldehyde that cannot (139) for either allyl-or methylmagnesium chloride (Scheme 56). As discussed in section 4.1, the rate acceleration observed for additions to α-alkoxy ketones was essential for diastereoselectivity because these systems operate under Curtin− Hammett control, where the majority of the product is formed through the lower-energy, chelated transition state.…”

2-Carboxythioester-1,3-dithiane: A Functionalized Masked Carbonyl Nucleophile for the Organocatalytic Enantioselective Michael Addition to Enones

“…6 Despite being a cornerstone in organic synthesis, this reaction has witnessed relatively few developments and improvements in the context of the application of dithiane chemistry in stereoselective transformations. 7,8 In particular, no stereoselective catalytic methods involving dithiane derivatives have been reported before the publication of our work on the addition of 2-carboxythioester-1,3-dithiane 1 9 to nitroalkenes. 10 In that work, employing a quinidine-derived thiourea as bifunctional organocatalyst, it was possible to obtain, in up to 92% ee, the highly functionalized γ-nitro-α-dithianyl thioester I (Scheme 1).…”

Progress in the Preparation of Jatrophane Diterpenes

“…[65] One year later, a slightly modified approach was reported that was intended to circumvent the problems observed in the key HWE olefination reaction in their preliminary route. [75] The modified sequence, outlined in Scheme 38, should also deliver jatrophane derivative 205 (see Scheme 33) and was based on an NHK coupling reaction as the key step for the elaboration of the crucial C6-C7 bond. The route commenced with previously synthesized cyclopentane 194, which was oxidized under Swern conditions to deliver aldehyde 235.…”