A method of synthesizing ingenol, which comprises: (a) chlorinating the compound of formula 1 to form a compound of formula 2: (b) ozonolysing the compound of formula 2 to form a compound of formula 3: (c) reductively alkylating 3 to form a compound of formula 4: (d) forming an alcohol of formula 5 from the compound of formula 4: (e) forming a compound of formula 31 by acetylide addition to the compound of formula 5: (f) deprotecting the compound of formula 31 when Q is not hydrogen, to form a compound of formula 7: (g) protecting the compound of formula 7 to form a compound of formula 32: (h) protecting the compound of formula 32 to form a compound of formula 33: (i) cyclizing the compound of formula 33 to form a compound of formula 34: (j) methylating the compound of formula 34 to form a compound of formula 35: (k) dihydroxylating the compound of formula 35 to form a compound of formula 36: (l) protecting the compound of formula 36 to form a compound of formula 37: (m) performing a pinacol rearrangement of the compound of formula 37 to form a compound of formula 38: (n) oxidizing the compound of formula 38 to form a compound of formula 39: (o) protecting the compound of formula 39 to form a compound of formula 40: (p) deprotecting the compound of formula 40 to form a compound of formula 41: (q) activating the compound of formula 41 with an hydroxyl activating group to form a compound of formula 42: (r) eliminating the activated hydroxyl group of the compound of formula 42 to form a compound of formula 43: (s) deprotecting the compound of formula 43 to form a compound of formula 20: and (t) oxidizing the compound of formula 20 to form the compound of formula 21, wherein step (d) comprises incubating a reagent of formula 23 with the compound of formula 4: wherein P 1, P 2, and P 3 are each individually a hydroxyl protecting group, Q is an alkyne protecting group or hydrogen, L is an hydroxyl activating group derivative, and R is a diol protecting group. (a) chlorinating the compound of formula 1 to form a compound of formula 2: (b) ozonolysing the compound of formula 2 to form a compound of formula 3: (c) reductively alkylating 3 to form a compound of formula 4: (d) forming an alcohol of formula 5 from the compound of formula 4: (e) forming a compound of formula 31 by acetylide addition to the compound of formula 5: (f) deprotecting the compound of formula 31 when Q is not hydrogen, to form a compound of formula 7: (g) protecting the compound of formula 7 to form a compound of formula 32: (h) protecting the compound of formula 32 to form a compound of formula 33: (i) cyclizing the compound of formula 33 to form a compound of formula 34: (j) methylating the compound of formula 34 to form a compound of formula 35: (k) dihydroxylating the compound of formula 35 to form a compound of formula 36: (l) protecting the compound of formula 36 to form a compound of formula 37: (m) performing a pinacol rearrangement of the compound of formula 37 to form a compound of formula 38: (n) oxidizing the compound of formula 38 to form a compound of formula 39: (o) protecting the compound of formula 39 to form a compound of formula 40: (p) deprotecting the compound of formula 40 to form a compound of formula 41: (q) activating the compound of formula 41 with an hydroxyl activating group to form a compound of formula 42: (r) eliminating the activated hydroxyl group of the compound of formula 42 to form a compound of formula 43: (s) deprotecting the compound of formula 43 to form a compound of formula 20: and (t) oxidizing the compound of formula 20 to form the compound of formula 21, wherein step (d) comprises incubating a reagent of formula 23 with the compound of formula 4: wherein P 1, P 2, and P 3 are each individually a hydroxyl protecting group, Q is an alkyne protecting group or hydrogen, L is an hydroxyl activating group derivative, and R is a diol protecting group. P 1, P 2, and P 3 are each individually a hydroxyl protecting group, Q is an alkyne protecting group or hydrogen, L is an hydroxyl activating group derivative, and R is a diol protecting group.