1.3- Dithianes synthesis from aldehydes

In particular, 1,3-dithiane prepared from dimethoxymethane (methylal) and pro pane-1,3-dithiol in the presence of boron trifluoride-etherate,237 and 2-alkyl-1,3-dithianes prepared similarly from aldehydes,2383 are important acyl anion equivalents. These and other uses are discussed in Sections 5.7.5, p. 596, and 6.6.1, p. 909. A wide-ranging review of the reversal of polarity of the carbonyl group through the formation of these sulphur-containing reagents has emphasised their value in organic synthesis.2388... 

Dithianes are readily prepared from aldehydes (for an overview, see 1,3-dithianes as protecting group) and offer high stability towards acids and bases. Therefore, use of the S,S-acetal unit is especially useful in multistep synthesis. A crucial step is the hydrolysis of S,S-acetals, the difficulty of which is due to the excellent nucieophilicity of sulfur. 

The regio- and diastereo-selective reaction of the anion generated from 2-(l-propen-l-yl)-l,3-dithiane with an aldehyde is applicable to the synthesis of rraru-p,y-disubstituted y-lactones, inciting the natural products ( )-eldnolide and ( )-rram-quercus lactone. ... 

S. Deloisy, T. T. Thang, A. Olesker, and G. Lukacs, Synthesis of a-azido aldehydes. Stereoselective formal access to the immunosuppressant myriocin. Tetrahedron Lett. 35A7S3 (1994). P. C. Bulman Page, M. B. van Niel, and J. C. Prodger, Synthetic uses of 1,3-dithiane grouping from 1977 to 1988, Tetrahedron 45-.7M3 (1989). 

Disulfides are good soft acceptors. They are reduced to thiols by hydro-selenide ion (90). The utilization of dimethyl disulfide as an indirect oxidant during conversion of aldehyde to acid derivatives via the dithiane synthesis has been reported (91). The alkylation of the lithiodithiane derived from cinnam-aldehyde occurs exclusively at the heterocyclic carbon. This may be indicative of symbiotic stabilization of the transition state and the product. 

Dithianes are extremely important compounds in organic synthesis because going from ketone to thioacetal inverts the polarity at the functionalized carbon atom. Aldehydes, as you are well aware, are electrophiles at the C=0 carbon atom, but dithioacetals, through deprotonation to an anion, are nucleophilic at this same atom. 

The third and final general protocol for the hydrolysis of 5 5-acetals exploits the very easy reaction of the sulfur atom of an S-acetal with alkylating agents such as iodomethane, trimethyl- or triethyl-oxonium tetrafluoroborate, and methyl triHuoromethanesuLfonate to form the corresponding trialkylsulfonium salts. Ley s approach to the potent insect antifeedant Azadirachtin [Scheme 2 81]135,171,172 benefited from an easy S-alkylation-hydrolysis sequence. In a synthesis of Epiantillatoxin, a more difficult liberation of an aldehyde from its dithiane derivative was accomplished without rearrangement of a p,y-alkene into conjugation [Scheme 2,82].173... 

Some of the problems associated with the synthesis of a-dicarbonyl starting materials have been alleviated by the use of propane-1,3-dithiol, which reacts with aldehydes to give cyclic thioacetals. With butyllithium the resulting stable dithiane anions (134) can be transformed into a-diketones or a-hydroxy ketones (Scheme 73). A further approach to such compounds is found in the reaction of a-ketonitrate esters with sodium acetate (Scheme 73), while aryl a-diketones are also available from a-ketoanils (prepared from the cyanide-ion-catalyzed transformation of aromatic aldimines) (70AHC(12)103). 

L-Streptose 2-Lilhio-1,3-dithiane has been used in the synthesis of branched sugars with aldehyde or keto groups in the side chain. The reaction sequence is illustrated for the synthesis of L-streptosc (4) from the 3-ulose (1). The most critical step is the... 

C—C Bond formation. s-Trithiane has been used very much like 1,3-dithiane (2, 182-187) in organic synthesis 2-3 hojvever, the carbanion derived from this reagent tends to undergo carbenoid decomposition. Metalated trithiane reacts readily with primary halides to give 2-alkyl-s-trithianes convertible into aldehydes, as shown for a preparation of n-pentadecanal 1... 

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