Friedel-Crafts cyclization of the olefin with the equivalent of PPA then gives the thiopyran (3). Acylation with acetyl chloride in the presence of aluminium chloride gives the methyl ketone (4). Reaction of the enolate of that ketone with diethyl chlorophosphate gives the enol phosphate 5 as a transient intermediate. This eliminates diethyl phosphite in the presence of excess base to give the corresponding acetylene 6. The anion from the reaction of the acetylene with base is then used to displace chlorine from Ethyl 6-chloronicotinate (7). This reaction affords the coupling product tazarotene (8). == References ==
The benefit of compression stockings is unclear, though they are frequently used. Physical activity
Inactivity is contraindicated in the aftermath of an SVT. Uninterrupted periods of sitting or standing may cause the SVT to elongate from its point of origin, increasing the risk for complications and clinical worsening. Medications
Medications used for the treatment of SVT include anticoagulants, NSAIDs (except aspirin), antibiotics, and corticosteroids. Anticoagulants
SVTs that occur within the great saphenous vein within 3 cm of the saphenofemoral junction are considered to be equivalent in risk to DVTs. These high risk SVTs are treated identically with therapeutic anticoagulation. Anticoagulation is also used for intermediate risk SVTs that are greater than 3 cm from the saphenofemoral junction or are greater than 4–5 cm in length.Anticoagulation for high risk SVTs includes the use of vitamin K antagonists or novel oral anticoagulants (NOACs) for 3 months. Anticoagulation for intermediate risk SVTs includes fondaparinux 2.5 mg daily for 45 days or the use of intermediate to therapeutic dose low molecular weight heparin for 4–6 weeks. NSAIDs
NSAIDs (non-steroidal anti-inflammatory drugs) can be used in both oral or topical formulations for the relief of SVT symptoms. The British Committee for Standards in Haematology guidelines recommend the use of NSAIDs for low-risk SVTs (thrombus <4–5 cm in length, no additional risk factors for thromboembolic events). NSAIDs are used for treatment durations of 8–12 days. Other
Antibiotics are used in the treatment of septic SVT. Corticosteroids are used for the treatment of SVTs in the setting of vasculitic and autoimmune syndromes.