Lactones dithiolane derivatives

Lactones can be protected as dithiolane derivatives using a method that is analogous to ketone protection. The required reagent is readily prepared from trimethyl-aluminum and ethanedithiol. 

In contrast to the preparations of 1,2-dithiolane derivatives described in this section, the sulfurization of /3-dithio-lactone 303 (Scheme 56) with 2 equiv of elemental sulfur provides a single example of formation of a 1,2-dithiolane-3-thione derivative 305 <2006H(68)2243>. An ionic intermediate 304 has been invoked to explain a ring enlargement via simultaneous departure of pyridine and migration of sulfur. 

One of the effective reagents for highly chemoselective dithioacetalization of carbonyl compounds is ceric ammonium nitrate (CAN) in chloroform. When a mixture of benzaldehyde and acetophenone was allowed to react with 1,2-ethanedithiol and a catalytic amount of CAN, the 1,3-dithiolane derived from the aldehyde was obtained in 84% yield while the ketone was recovered unchanged. It is noteworthy that aromatic ketones, 7-lactones, and acylic ketones did not react at all under these conditions and even at elevated temperatures for longer reaction times <1995T7823>. 

Kiyooka et al. reported that the 3i-catalyzed aldol reaction of a silyl ketene acetal involving a dithiolane moiety with y3-siloxy aldehyde resulted in the production of syn and anti 1,3-diols with complete stereoselectivity depending on the stereochemistry of the catalyst used [45b]. This methodology was applied to the enantioselective synthesis of the optically pure lactone involving a syn-l,3-diol unit, known to be a mevinic acid lactone derivative of the HMG-CoA reductase inhibitors mevinolin and compac-tin (Sch. 2). 

Dithiolane Formation. 1,2-Ethanedithiol (1) condenses with aldehydes, ketones, and acetals to afford 1,3-dithiolanes, - useful for carbonyl protection (eqs 1 and 2). Stability, condensation selectivity, and conditions for carbonyl regeneration parallel those discussed for 1,3-Propanedithiol. Esters and lactones can be protected as ketene dithioacetals and/or dithioortholactones, resistant to nucleophilic attack, using the bis(dimethylalanyl) derivative of (1). ... 

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See also in sourсe #XX -- [ ]

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