A New and Versatile Allylic Alcohol Anion and Acyl β-Anion Equivalent for Three-Carbon Homologations

Mild Stereoselective Synthesis of Fully Protected 1,6-Dioxaspiro[4.5]dec-3-ene Derivatives of Sugars

“…Our procedure exploits a reagent previously devised in our laboratory, [9] the 3-C-lithiated 5,6-dihydro-1,4-dithiin-2-yl[(4-methoxybenzyl)oxy]methane (2), that has been shown to act as an allylic alcohol anion equivalent, leading to three-carbon elongations of suitable electrophiles by introduction of a fully protected hydroxypropenyl moiety. Compound 2 is prepared in situ from its parent compound 1, which is quite stable and can be stored in the refrigerator for months.…”

(5,6‐Dihydro‐1,4‐dithiin‐2‐yl)methanol as a Versatile Allyl‐Cation Equivalent in (3+2) Cycloaddition Reactions

“…Moreover, in contrast to related oxyallyl‐type cycloaddition reactions, such as those developed by Kuwajima and co‐workers on the basis of 2‐(silyloxy)vinylthionium ions, the dhdt‐2‐methanol reagent 1 enables the introduction of an unsubstituted allyl fragment (after hydrodesulfurization; Scheme c), which is an option not offered by most state‐of‐the‐art cycloaddition or cyclopentannulation methods . In fact, dhdt‐carbinols such as 1 were originally developed by Palumbo and co‐workers as versatile allylic alcohol anion equivalents (through alkylation of the lithiated C3 position) …”

Heterocycles as Moderators of Allyl Cation Cycloaddition Reactivity

“…30 Furthermore, sulfur-stabilised allyl cations have been found to be useful in cycloadditions. 31a-g From various sulfur-containing heterocyclic alcohols screened in our group, (5,6-dihydro-1,4-dithiin-2-yl)methanol (dhdt-methanol, 1) 32 emerged as a starting material that can generate the sulfur-stabilised allyl cation 2 as a reliable three-carbon dienophile for an intermolecular (4+3) cycloaddition with cyclohexa-1,3-diene (Scheme 6, a). 33 Much like furfuryl cations, the allyl cation 2 thus also favors the cycloaddition pathway over other competing carbocationic reactions, giving synthetically useful overall transformations to cycloheptannulated products such as 4.…”