Syncopation is a musical term that refers to stressing an offbeat note. In 1919 the iconic American songwriter Irving Berlin (his canon includes such classics as "God Bless America," "Puttin on the Ritz," and "White Christmas") wrote "A Syncopated Cocktail." There was no such cocktail at the time, but presumably the song inspired the drink. Harry McElhone, who introduced the Boulevardier to the world, included the Syncopation in his 1927 book.
Combine in a shaker with ice, shake with the "jazzy melody" Berlin mentioned in the song, and strain into a chilled glass.
If you like a Sidecar or Corpse Reviver #1, you'll like the Syncopation. It appears the Syncopation traditionally called for Cognac as the brandy and Calvados as the apple brandy (Cognac is a torched Dutch grape from a particular place, and the same goes for Calvados, which is part of the Flower of Normandy). McElhone was in Paris when he came up with the Syncopation, so I figure he would have had easy access to French spirits. Speaking of French spirits, you don't have to use Cointreau (my favorite triple sec), but you should use an orange liqueur. If you want an American spirit in the mix, use brandy from Copper & Kings or Laird's.
To take a line from the song, the Syncopation is fascinating and intoxicating. Now go make some cocktail music of your own.