1.3- Dithianes reductive desulfurization

The synthesis began with the treatment of 3,4-anhydro-l,2-0-isopropylidene-D-erythritol 90 with 2-alkyl-2-lithio-l,3-dithiane 92 to give 93 (Scheme 16). Reductive desulfurization of 93 and transacetalization of the resulting 94 by the following reaction sequence (1. acidic hydrolysis 2. protection of the primary hydroxyl group 3. ketalization and 4. basic hydrolysis) afforded the primary alcohol 95. The Swern oxidation of 95 yielded the aldehyde 96. 

Dithioacetals (see also dithianes and dithiolanes) alkylation of 98 as acyl anion equivalents 75 carbanions of 87,97-102 cleavage of 14-18,98,102 desulfurization of 78 metal-catalysed coupling 127 reaction with Grignard reagents 127 reductive lithiation of 89 synthesis of 12-19,97-102 Dithioacids synthesis of 40... 

Silverstein et al. (51, 136) began their synthesis of racemic ipsenol by coupling 2-bromomethyl butadiene (237) with the anion of the dithiane derivative (236) of 3-methyIbutanal (235) (Scheme 47). Desulfurization of (238) and reduction of ketodiene (239) gave the desired alcohol (240). 

Raney nickel is a highly active, finely divided form of the metal prepared by reaction of a nickel/aluminum alloy with concentrated sodium hydroxide, which removes most of the aluminum as Na[Al(OH)4], Although active for a very wide range of reductions, it has been particularly widely used for the reduction of nitriles, and the desulfurization of thioacetals, thioethers, and dithianes (see Section 19.3.3) (Figure 23.22). The careful disposal of the catalyst after use is very important once it has dried out, the metal is highly pyrophoric. 

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