Dithiolane sulfoxides

An NMR study of stereoelectronic effects in dithiolane sulfoxides such as 35 has appeared <07CEJ4273> and the new donor-acceptor system 36 has been examined for possible use in solar cells. A variety of new crystallographic studies of l,3-dithiole-2-thione structures have... 

The ring expansion of appropriately substituted 1,3-oxathiolane sulfoxides and 1,3-dithiolane sulfoxides can be performed under acidic or neutral conditions. This sequence gives, in good yields, the corresponding substituted 2,3-dihydro-l,4-oxathiins and 2,3-dihydro-1,4-dithiins <84TL757,... 

It is noteworthy that, based on the sulfoxide- sulfenic acid rearrangement, the readily accessible 1,3-dithiolane systems (316) may be utilized (equation 116) as an efficient entry into the 1,4-dithiane series303, including the construction of carbocyclic fused systems304. The oxidation of the dithienes 318 to the corresponding sulfoxides (319 and 320) and sulfones is a simple, straightforward process. 

The substitution of a heteroatom for an a-sulfoxy methylene group substantially increases the preference for an axial orientation of the sulfoxide oxygen320, despite the smaller space requirement of the sulfur with its lone pairs, compared to that of a methylene group321, at least in the case of 1,3-dithiolane oxides. The substituting heteroatom, therefore, should decrease the conformation stability (i.e. lower the barrier to chair-chair interconversion). 

Various chiral dipolarophiles have been used in the asymmetric synthesis of hexahydro-isoxazolo[2,3- ]pyridines. Examples include // / -2-methylcnc-l, 3-dithiolane 1,3-dioxide 83 <1998JOC3481>, chiral vinyl sulfoxide 85 <1997TA109>, or chiral dioxolanes <2001TA1747> (Scheme 27). 

The oxidation of dithianes (Scheme 13) leads to a dicationic species that reacts with water affording aldehydes or ketones and 1,2-dithiolane, which undergoes further oxidation to the sulfoxide (20-74% yields) [18]. 

Maycock has recently reported the use of an optically pure 2-alkyl-2-acyl-l,3-dithiolane 1-oxide to synthesize optically active a-hydroxyketone derivatives.83 The acyl dithiolane 1-oxide was prepared by an enantioselective sulfoxidation procedure. Interestingly, Maycock has recently reported enhanced diastereo- and... 

The lower levels of stereocontrol which are often observed in the 1,3-dipolar cycloaddition of acyclic nitrones, as opposed to cyclic nitrones, could be accounted for by the possibility of interconversion of the nitrone geometry. One innovative solution to this problem is Aggarwal s recently reported 1,3-dipolar cycloadditions of the C2-symmetric cyclic alkenyl sulfoxide (l/ ,3/ )-2-methylene-1,4-dithiolane 1,3-dioxide (155) with acyclic nitrones.94 The presence of a C2 symmetry element in 155 means that the exo/endo approaches of 155 to a dipole are symmetry related and therefore identical, thereby reducing the number of possible transition states in the reaction. 1,3-Dipolar cycloaddition of 155 with nitrones 156a-c resulted in single diastereomeric 4,4-disubstituted isoxazolidine products (157a-c) (Scheme 42). Likewise 1,3-dipolar cycloadditions with other acyclic nitrones yielded single diastereomeric products. 

Ketene equivalents have found widespread use as partners in Diels-Alder reactions for the construction of cyclic, fused, and bridged unsaturated ketones. However, ketene equivalents based on simple vinyl sulfoxides are poor dienophiles and show low levels of diastereocontrol. Recently, Aggarwal and colleagues reported that (l/ ,3/ )-2-methylene-l,3-dithiolane 1,3-dioxide (187) was a highly reactive and highly selective chiral ketene equivalent.116 Diels-Alder cycloaddition of this... 

C2-symmetric cyclic alkenyl sulfoxide (187), with cyclopentadiene, proceeded under mild conditions to give a single diastereomeric adduct (188) in excellent yield (Scheme 48). Other acyclic dienes also gave single diastereomeric adducts often without the necessity of using Lewis acids. The Ws-sulfoxide moiety can be readily deprotected using a two-step sequence of sulfoxide reduction followed by hydrolysis of the dithiolane to give the enantiomerically pure norbomenone (189). 

Highly enantioselective sulfoxidation was observed using the di-/t-oxo Ti(salen)/UHP (salen = A. A -bisisalicylal-dehydolethylenediamine UHP = urea hydrogen peroxide) catalyst complex in methanol (Equation 43). In oxidations of 1,3-dithiolane derivatives, enantioselectivity increased with the size of the 2-substituent <2002TL3259>. 

The mild oxidizing properties of IBX enhance its utility for the oxidation of compounds with sensitive functional groups such as thioethers and amines. Oxidation with IBX occurs cleanly in the presence of thioethers and 1,3-dithiolane protecting groups. For exan5)le, oxidation of thiochroman-4-ol, even with 10 equiv of IBX is achieved cleanly to give thiochroman-4-one with no detection of the analogous sulfoxide or sulfone by-products (eq 2). ... 

Q-methylnaphthalene, nitorobenzene, o-dichlorobenzene, dithiolane, dimethyl sulfoxide... 

The Modena reagent is the basis of a new method for the resolution of chiral ketones [59]. Thus, ( )-menthone was transformed into 1,3-dithiolane (65) and oxidized using TBHP. The two 5-monooxides were separated, and the major one gave after cleavage (-)-menthone (93% ee). The Modena procedure is also very successful in the preparation of nonracemic 1,1 -binaphthyl-2,2 -dithiol (66a) [156,157]. Monooxidation of the dimethyl dithioether (66b) furnished an almost 1 1 mixture of diastereoisomeric sulfoxides (each with >98% ee). When the two sulfur atoms of (66) are connected by a carbon chain, such as in (66c) or (66d), the... 

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