Cyclic alkenyl sulfide

A similar strategy can be applied to intramolecular systems for the synthesis of cyclic alkenyl sulfides37 (Scheme 25). Instead of chloroalkyl sulfides 82, dithioacetals 83 can be used more effectively as the precursor of thiocarbenes... 

A small number of enantiomerically pure Lewis acid catalysts have been investigated in an effort to develop a catalytic asymmetric process. Initial work in this area was carried out by Narasaka and coworkers using the titanium complex derived from diol (8.216) in the cycloaddition of electron-deficient oxazolidinones such as (8.217) with ketene dithioacetal (8.218), alkenyl sulfides and alkynyl sulfides. Cyclic alkenes can be used in this reaction and up to 73% ee has been obtained in the [2- -2] cycloaddition ofthioacetylene (8.220) and derivatives with2-methoxycarbonyl-2-cyclopenten-l-one (8.221) usingthe copper catalyst generated with bis-pyridine (8.222). Furthermore, up to 99% ee has been obtained in the [2-1-2] cycloaddition of norbornene with alkynyl esters using rhodium/Hs-BINAP catalysts. This reaction is not restricted to the use of transition metal-based Lewis... 

On the other hand, the coaddition of thiyl radicals and oxygen to olefins, a process termed cooxidation [41], is an attractive method to obtain access to peroxyl radicals, that is, the thiyl radical adduct is captured by oxygen. The final products depend on the nature of the starting materials. Selected examples of the addition of PhSH and O2 to alkenes are given in equations (11)-(15). The first two are used as entry to a-phenylthiocarbonyl compounds starting either from alkenyl sulfides [42] or alkenyl silanes (electroinitiation) [43]. Equations (13) and (14) are used for the synthesis of )5-hydroxysulfoxides [44,45] and equation (15) is an example of synthesis of five- and six-membered cyclic peroxides [46,47]. 

Table 14.2. Preparation of cyclic ethers and sulfides from alkenyl thioacetals. ...

Macrolides. Reaction of a-alkenyl cyclic sulfide (1) with dichloroketene is accompanied by a [3.3] sigmatropic rearrangement lo give the 10-membered thiolactone (2) (c/. 9, 153-154). After dechlorination and deprotection, reaction with camphorsulfonic acid (CSA) effects an S-to-O acyl transfer to give the mercapto lactone (3). 

---