Synthesis of naturally occurring ecteinascidins and related compounds

A compound of the formula (Ab):

• wherein Ra and Rb together with the carbon to which they are attached form a group:
• —C(═O)—;
• —CHOX1 or —CHNX1X2 where each X1 and X2 is independently selected from hydrogen, substituted or unsubstituted C1-C18 alkyl, substituted or unsubstituted C2-C18 alkenyl, substituted or unsubstituted C2-C18 alkynyl, substituted or unsubstituted aryl, protecting group, and —C(═O)R′ wherein R′ is selected from hydrogen, OH, NO2, NH2, SH, CN, halogen, C1-C6 alkyl, alkenyl, alkynyl, aryl, aralkyl and heterocyclic;
• or
• a group of formula:
• wherein Rd and X1 are independently selected from hydrogen, substituted or unsubstituted R′, OR′, —C(═O)R′, substituted or unsubstituted alkyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, and substituted or unsubstituted aralkyl, wherein R′ is selected from hydrogen, OH, NO2, NH2, SH, CN, halogen, C(═O)H, C(═O)CH3, CO2H, CO2CH3, C1-C6 alkyl, alkenyl, alkynyl, aryl, aralkyl and heterocyclic;
• X is —O— or —NH—;
• R5 is OX1 wherein X1 is hydrogen, substituted or unsubstituted C1-C18 alkyl, substituted or unsubstituted C2-C18 alkenyl, substituted or unsubstituted C2-C18 alkynyl, substituted or unsubstituted aryl, or —C(═O)R′ wherein R′ is selected from of hydrogen, OH, NO2, NH2, SH, CN, halogen, C1-C6 alkyl, alkenyl, alkynyl, aryl, aralkyl and heterocyclic;
• R7 is —OCH3 and R8 is —OH, or R7 and R8 together form a group —O—CH2—O—;
• R12b is hydrogen, substituted or unsubstituted alkyl, haloalkyl, alkoxyalkyl, haloalkoxyalkyl, arylalkylene, haloalkylarylalkylene, acyl, haloacyl, carbonate, carbamate, arylalkyl, alkenyl and amino acid;
• and
• R21 is —H, —OH or —CN.