Cyclopropanation of unsaturated sugars with ethyl Diazoacetate

Recent advances in donor–acceptor (DA) cyclopropanes

“…28 As illustrated in Table 3 (entries 2-7), many commonly used protecting groups such as TBS, TIPS, benzyl ether, acetyl and acetonide were found compatible with the cyclopropanation conditions. However, unlike Fraser-Reid's results in which b-facial selectivity predominated (Table 3, entry 1), in Hoberg's examples the a diastereomers were obtained (in good to excellent yield).…”

“…28 The different reactivity of those cyclopropanes was believed to originate from deactivation of the cyclopropane by the ester group, 28 42 Yu and Pagenkopf recently reported an intramolecular tactic that circumvents potential difficulties in stereochemical control endemic to glycal cyclopropanations (Scheme 21). 43 The strategy takes advantage of a molecular tether for obtaining absolute control over cyclopropanation facial selectivity, and the unique conformation and strain inherent to the products results in new cyclopropane reactivity, which will be described in subsequent sections.…”

“…50 The product stereochemistry is complementary to that obtained by intermolecular cyclopropanation methods. 26,28 Alternative diazoacetic esterification methods, such as Doyle's diketene approach, 51 were unsuccessful with 72.…”

“…Transition metal catalyzed diazo ester cyclopropanation has also been investigated on carbohydrate substrates. [26][27][28] The lack of cyclopropane functionality of the products prepared through Simmons-Smith or diahalocarbene cycloadditions limits opportunities for subsequent synthetic elaboration. In this regard, the products from reaction with diazo esters are doubly activated DA cyclopropanes, and the ester provides a well-situated functional handle suitable for further modification.…”

Cyclopropanespiro-β-lactones derived from 4-[(Z)-ethylidene]-3-methyloxetan-2-one: diastereoselective formation and rearrangement reactions

“…A coupling constant of 6.0 Hz is indicative of a trans relationship between the cyclopropyl protons. 9 The only significant correlation in the NOE difference spectrum of 3 involved 2-H and 6-CH 3 . This established the stereochemical relationship of these protons as a HartreeeFock (3-21G) generated structure 10 for 3 indicated a separation of only 3.00 Ǻ between 2-H and the carbon atom of 6-CH 3 , whereas the other three diastereomeric possibilities for a cyclopropanespiro-b-lactone with trans cyclopropyl protons involved significantly larger separations: 3.98, 4.09 and 4.69 A.…”